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Mechanical and magnetic properties of metal fibre networks, with and without a polymeric matrix
Abstract
Bonded networks of metal fibres are highly porous, permeable materials, which often exhibit relatively high strength. Material of this type has been produced, using melt-extracted ferritic stainless steel fibres, and characterised in terms of fibre volume fraction, fibre segment (joint-to-joint) length and fibre orientation distribution. Young’s moduli and yield stresses have been measured. The behaviour when subjected to a magnetic field has also been investigated. This causes macroscopic straining, as the individual fibres become magnetised and tend to align with the applied field. The modeling approach of Markaki and Clyne, recently developed for prediction of the mechanical and magneto-mechanical properties of such materials, is briefly summarised and comparisons are made with experimental data. The effects of filling the inter-fibre void with compliant (polymeric) matrices have also been explored. In general the modeling approach gives reliable predictions, particularly when the network architecture has been characterised using X-ray tomography.
... Artificial cilia are long rod-like or plate-like slender bodies made of magnetoactive elastomers ( Brigadnov and Dorfmann, 2003;Rudykh and Bertoldi, 2013;Galipeau et al., 2014;Goshkoderia and Rudykh, 2017 ) that easily deflect when loaded by magnetic fields (see Fig. 1 a-c). Also, materials that are made of a network of slender bodies,(e.g., long rods or thin plates) in bonded fiber networks ( Clyne et al., 2005 ) (see Fig. 1 d), porous metals ( Boonyongmaneerat et al., 2007 ) and cellular solids ( Gibson and Ashby, 1999 ), feature strongly-enhanced magnetostrictive properties compared to dense materials. For the application and design of this class of materials, coupled magnetoelastic structure-property relations need to be determined. ...
... (c) Plate-like artificial cilia that are actuated by a planar rotating magnetic field (blue arrows in the inset) resulting in an asymmetric actuation pattern resulting in fluid flow ( Khaderi and Onck, 2012 ). (d) Scanning electron micrograph of a bonded metallic fiber network for magnetic actuation in biomedical applications ( Clyne et al., 2005 ). The figures (a) and (b) are reproduced, with permission, from Zhang et al. (2018) , figure (c) from Khaderi and Onck (2012) and figure (d) from Clyne et al. (2005) . ...
... (d) Scanning electron micrograph of a bonded metallic fiber network for magnetic actuation in biomedical applications ( Clyne et al., 2005 ). The figures (a) and (b) are reproduced, with permission, from Zhang et al. (2018) , figure (c) from Khaderi and Onck (2012) and figure (d) from Clyne et al. (2005) . (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) ...
... (1)], it then exhibits a O(1/ ) asymptotic behavior whenever microscale variations of the type x/ are present. In this sense, our formulation considers locally unbounded body forces, which are regular and well defined in the context of the elastic problem (8)(9)(10)(11)(12), nonetheless asymptotically behaving as 1/ when representation (15) holds. The systems of PDEs (8)(9)(10)(11)(12) turn out to be homogenizable assuming microscale periodicity, as done in the rest of this work. ...
... In this sense, our formulation considers locally unbounded body forces, which are regular and well defined in the context of the elastic problem (8)(9)(10)(11)(12), nonetheless asymptotically behaving as 1/ when representation (15) holds. The systems of PDEs (8)(9)(10)(11)(12) turn out to be homogenizable assuming microscale periodicity, as done in the rest of this work. ...
... We show that the model (8)(9)(10)(11)(12) is homogenizable, even though the body force acting on the composite is in general locally unbounded (see Remark 1). The balance equations (63) obtained via asymptotic homogenization Homogenization for composites subject to inhomogeneous potentials 155 of the problem (8-12) read as a well-defined linear elastic model (once appropriate external boundary conditions on ∂Ω H are prescribed) in terms the leading order displacementū in the homogenized domain Ω H . ...
We derive the new effective governing equations for linear elastic composites subject to a body force that admits a Helmholtz decomposition into inhomogeneous scalar and vector potentials. We assume that the microscale, representing the distance between the inclusions (or fibers) in the composite, and its size (the macroscale) are well separated. We decouple spatial variations and assume microscale periodicity of every field. Microscale variations of the potentials induce a locally unbounded body force. The problem is homogenizable, as the results, obtained via the asymptotic homogenization technique, read as a well-defined linear elastic model for composites subject to a regular effective body force. The latter comprises both macroscale variations of the potentials, and nonstandard contributions which are to be computed solving a well-posed elastic cell problem which is solely driven by microscale variations of the potentials. We compare our approach with an existing model for locally unbounded forces and provide a simplified formulation of the model which serves as a starting point for its numerical implementation. Our formulation is relevant to the study of active composites, such as electrosensitive and magnetosensitive elastomers.
... In recent years, metal porous materials have been used due to their unique properties and the combination of structural and functional material properties [1][2][3]. Widely used in biological, medical [4][5][6], aerospace [7] and industrial applications [8][9][10][11][12], the high demand for green materials in various fields has driven the development of metal foam. Porous metal foam structures with high specific surface area, high permeability properties and high mechanical strength are being explored as an alternative material to conventional heat exchangers. ...
... In order to obtain the total convective heat transfer Q during the experiment, the heat transfer coefficient h needs to be determined. The total heat was obtained using Equation (2) and averaged when the heat absorbed by the cold fluid was in equilibrium with that of the hot fluid (∆Q < 5%). The log-average temperature difference is calculated using Equation (3) and the total heat transfer coefficient K is calculated from Equation (4). ...
The performance of an electronic radiator filled with metal foam with a porosity of 96% was studied. The effect of the factors including the flow rates, the pores per linear inch (PPI) and the numbers of fins was analyzed. The results show that the electronic radiator with metal foam reflects a stronger ability of the heat transfer compared to the electronic radiator without metal foam. With the increase in the flow rate between 10 L/h and 60 L/h, the heat transfer coefficient of both of the two electronic radiators will be improved, but it is also dependent on the number of fins. In this study, we find that the heat transfer coefficient first increases and then decreases with the number of fins. The optimum number is three. As for the effect of the PPI, the higher the PPI, the larger the heat transfer coefficient, while the pressure drop always increases with the flow rates’ increase, the pores per linear inch (PPI) and the numbers of fins.
... These materials show large potential for application as actuators and sensors in multifunctional devices, such as micro-and nanoelectromechanical systems (c) Plate-like artificial cilia that are actuated by a planar rotating magnetic field (blue arrows in the inset) resulting in an asymmetric actuation pattern resulting in fluid flow [5]. (d) Scanning electron micrograph of a bonded metallic fiber network for magnetic actuation in biomedical applications [6]. (a) and (b) are taken from [7]. ...
... Here, magnetically-responsive materials are especially attractive, because the magnetic fields can be readily created and do not interfere with biological samples in e.g., biosensors, in contrast to electric fields or temperature. This has led to a new and rapidly growing field in microfluidic systems and lab-on-chip devices in which magnetically-actuated artificial cilia are fiber networks [6] (see Fig. 1 d), porous metals [12] and cellular solids [13],feature strongly-enhanced magnetostrictive properties compared to dense materials. For the application and design of this class of materials, coupled magnetoelastic structureproperty relations need to be determined. ...
Magneto-responsive slender bodies are used in a range of promising applications, such as artificial cilia, magnetic fiber networks and cellular actuators. To accurately describe the magneto-elastic deformations, both the demagnetization field as well as the resulting magnetic loads on the body should be properly accounted for. The calculation of the demagnetization field for a general sample shape is very challenging, which has hampered the experimental characterization of the intrinsic magnetic and magnetoelastic properties. Here, a methodology is developed to accurately calculate the demagnetization field for slender bodies, i.e., for long beams having a rectangular or circular cross-section. We propose two different expressions for the magnetic load on slender bodies. To validate the two expressions, we solve the magnetic buckling problem for cantilever beams using an analytical approach for small deflections. We compare the critical buckling fields with an energy approach and with experimental results from three different studies. The load and energy methods were found to be similar and to correspond very well with the experimental data. To also validate our slender body approach (i.e., demagnetization field calculation and magnetic load expression) for large deflections, we analytically solve for the large (postbuckling) rotational deformation of slender beams. To do so, we formulated a weak form of the governing equations using a variational approach, which can be readily solved using finite elements and does not require a discretization of the space surrounding the magnetic material. We use this generic 3D continuum formulation as a starting point to derive the governing equations for slender bodies, which can be solved in a weak sense to find an approximate analytical formulation for large deflections and non-linear ferromagnetic materials. We compared the analytical results with experimental data on the post-buckling deformation of long cantilever beams and found excellent agreement. We anticipate that our results will be valuable for magneto-elastic (soft) robotics, homogenization approaches of magneto-elastic constitutive relations and other applications where strong magneto-elastic coupling is important.
... The mechanical properties are enhanced with increasing sintering contact points per unit volume and the bonding intensity. Some analytical models have been developed based on the assumption of affine deformation of the fibre network ( Clyne et al., 2005;Markaki and Clyne, 2005;Picu, 2011; Tsarouchas and Markaki, 2011 ). The relative density can significantly affect the strength and stiffness of porous materials ( Gibson and Ashby, 1997;Chen et al., 1999;Jin et al., 2013;Won et al., 2013;Zhu et al., 20 01, 20 0 0, 1997 ); however, it is difficult to control the relative density in the manufacturing process. ...
... X-ray tomography has been utilized to extract the exact architectural characteristics from the very complicated porous fibre-network material and the data are used to reconstruct the geometrical model for this material ( Clyne et al., 2005;Tsarouchas and Markaki, 2011 ) as shown in Fig. 1 a; however, this technique is very computationally challenging. Finite element models are an attractive approach to constructing the complex stochastic fibre-network structure based on fundamental geometrical parameters extracted from the X-ray computed tomography. ...
Fibre network materials constitute a class of highly porous materials with low density, promising for functional and structural applications; however, very limited research has been conducted, especially on simulation and analytical models. In this paper, a continuum mechanics-based three-dimensional periodic beam-network model has been constructed to describe the stochastic fibre network materials. In this model, the density of the cross-linkers is directly related to the relative density of the fibre network materials, and the cross-linkers are represented by equivalent beam elements. The objective of this work was to delineate the elasto-plastic behaviour of the stochastic fibre network materials. Characteristic stress and strain derived from the total strain energy density have been adopted to reveal the yielding behaviour of the fibre networks. The results indicate that the stochastic fibre network materials are transversely isotropic. The in-plane stiffness and strength are much larger than those in the out-of-plane direction. For the fibre network materials with a small relative density, the relationship between the uniaxial yield strength and the relative density is a quadratic function in the x direction and is a cubic function in the z direction, which agree well with our dimensional analysis and are consistent with the relevant experimental results in literature. The yield surface depends strongly on the relative density and the connection between fibres.
... The compressive yield stress of the SSSFFs with 82.3% porosity is about 4 MPa. Clyne et al. [11] measured the yield stress of bonded networks of metal fibers using melt-extracted ferritic stainless steel fibers. The yield stress of SSSFFs with 85% porosity and fiber segment aspect ratio of 6 is about 1 MPa. ...
... The yield stress of SSSFF samples with 75%, 80%, and 85% porosity achieves 25 MPa, 17.5 MPa, and 10.5 MPa, respectively. It can be seen that the tensile strength and yield stress of the SSSFFs are far beyond that of SSSFFs prepared by Clyne et al. [11] and Markaki et al. [12]. Thus, this kind of SSSFFs possesses high strength as well as high porosity. ...
A novel sintered stainless steel fiber felt (SSSFF) with rough surface morphologies and high strength as well as high porosity is fabricated by solid-state sintering of stainless steel fibers produced by cutting method. The rough surface morphologies are characterized by laminar and jagged structures formed on the surface of stainless steel fibers. The SSSFF with 85% porosity sintered at 1200°C for 60 min exhibits tensile strength of 19 MPa and yield stress of 10.5 MPa. The influence of sintering parameters on surface morphologies and tensile strength is investigated. The experimental results show that the rough surface structures will disappear gradually when sintering temperature is 1300°C or sintering time is excessive, that is, 240 min when sintering temperature is 1200°C. The SSSFF with high porosity presents high tensile strength when sintering temperature ranges from 1100°C to 1200°C and sintering time is from 60 min to 120 min. In addition, the fracture mechanism of the SSSFF is investigated when subjected to uniaxial tensile load.
... In particular, published experiments reveal that the structural randomness affects the 3DRF materials' mechanical properties [1,9,10]. Currently, a number of theoretical models [11][12][13] based on affine approximations have been proposed to study the mechanical properties of 3DRF materials. In this report, the structural randomness is described by a random distribution function for fibre orientation. ...
... where C ij is given in Eq. (11). For the transversely isotropic materials, Eq. (15) yields a value of zero. ...
Three-dimensional (3D) random fibrous materials exhibit extraordinary mechanical properties due to their complex morphological characteristic of bonded fibre networks on the meso-level. Based upon experimental characterisation, a simplified numerical model is presented that reveals the disordered features of bonded fibre networks and allows investigation of the tensile behaviour of 3D random fibrous (3DRF) materials. The calculated results' dependence on the quantity of numerical samples, mesh density and model size is analysed using finite element analysis (FEA); consequently, an optimised FEA model is obtained. The 3DRF materials' tensile behaviour is then predicted using the optimised FEA model. The calculated results agree well with the experimental data. Moreover, the predicted failure mechanism is consistent with SEM observations. The experimental data thus validate the FEA model. On this basis, we conduct a comprehensive investigation to understand the influences of the fibres' deformation mode, the bonding properties and the proportion of the constituent fibres on the macro-mechanical properties of 3DRF materials. These analyses provide insight into the mechanical behaviour of such materials.
... A random assembly is analogous to a dispersion of nanowires at high density, whereby the nanowires are oriented haphazardly with respect to each other. Paper and steel wool resemble such a structure; [83] however, at the nanoscale, materials such as carbon nanotubes (CNTs) are regularly mixed into polymers for the purpose of mechanical reinforcement. Nanofibrous membranes have been prepared using such a mesh of CNTs for ultrafiltration of oil and proteins from wastewater. ...
Nanowire-like materials exhibit distinctive properties such as optical polarisation, waveguiding, and hydrophobic channelling, amongst many other useful phenomena. Such 1-D derived anisotropy can be further enhanced by arranging many similar nanowires into a coherent matrix, known as an array superstructure. Manufacture of nanowire arrays can be scaled-up considerably through judicious use of gas-phase methods. Historically, the gas-phase approach however has been extensively used for the bulk and rapid synthesis of isotropic 0-D nanomaterials such as carbon black and silica. The primary goal of this review is to document recent developments, applications, and capabilities in gas-phase synthesis methods of nanowire arrays. Secondly, we elucidate the design and use of the gas-phase synthesis approach; and finally, remaining challenges and needs are addressed to advance this field.
... Whether it be random or periodically ordered, a one-directional bundle of infinite fibers makes the composite medium bi-continuous in the fiber direction and phase cocontinuity is ensured in all fiber directions of multi-directional such networks which are through-sample spanning. Such networked fiber structures can be found in vary many different materials the matrix phase of which can have different (elasto-viscoplastic) behavior type, including possible damage, and most cases the fiber phase combines both stretching and bending straining modes at least in some ranges of deformation [69][70][71][72]. ...
In this thesis, we present the result of the contact between two domains which in origin are very distant: the synthesis of new theory-driven conceived materials, the so-called metamaterials, and an homogenization framework based on some particular mathematical objects called Green operators, fruitfully used for describing the effective properties of composite materials. So, the main idea driving this thesis work is todesign and study (and, possibly, to produce and measure) a mechanical system which we could call composite metamaterial. It should have both the enhanced properties of composite materials and of the smart architectures characteristic of metamaterials.The idea above described is obviously of not simple actuation and it obliges to face with very hard mathematical and technical problems. In this thesis work, we try to explain the first tentative to reach this very ambitious project. The first chapter of this thesis is devoted to the description of a particular metamaterial we have chosen as a reference for developing the composite. It is called the pantographic metamaterial and we are interested in its deformation enhanced properties, as, for example, large deformation ranges and late damage onset. We want to underline here that, from a mathematical point of view, the pantographic metamaterial is described by means of a generalized theory. Specifically, the presence of the microstructure makes it necessary to adopt a second gradient model for taking into account all its exotic effects. Experimental tests for 3D pantographic structures are presented in the second Chapter. A comparison with thee valuations obtained by means of the model developed in the previous chapter is performed and the limits of this model are experimentally evaluated. The above mentioned tests are finally analysed by using the Digital Image Correlation techniques, which allow to measure in a very precise way the displacement and the deformation fields.In the third and fourth chapters, the Green tensors homogenization framework is presented and used for modelling the pantographic-inspired material. This homogenization framework has some advantages: (i) it is very simple to be applied (in contrast with the Gamma convergence techniques needed to formally derived the homogenized description of the pantographic metamaterial); (ii) the result of this homogenization procedure consists in the direct access to the effective properties of the material; (iii) it is linear and, for this reason, the algorithmic code written to obtain the effective properties is very fast compared to the FEM based codes for numerically simulating the pantographic metamaterial.In the last Chapter, the damage modelling in pantographic structures is approached. The discussion about damage presented in this thesis is related to the deformation features of the interconnecting pivots: this allows us to carry on some comparisons with the pantographic-inspired material, where, as it is shown in Chapter 4,the role of the pivots is played by the matrix phase. On the basis of simple criteria, the damage forecasting ismade possible if the pivots have specific geometrical features.
... These models also considered anisotropic fibre orientation distributions and moisture dependent material properties. Other works, mostly performed earlier, focussed on establishing a relationship between the micro-structural and the macroscopic responses of fibrous network (Alava and Ritala, 1990;Åström et al., 1994;Clyne et al., 2005;Wu and Dzenis, 2005;Tsarouchas and Markaki, 2011). ...
Paper is a material exhibiting a complex microstructure that is composed of a network of fibres at the micro-level. When subjected to external loading or variations in moisture conditions over different time scales, changes in strain that are non-linear with respect to time are observed at the sheet level (macro-scale). In order to investigate this time-dependent behavior of paper, a creep power law model is implemented within a finite element approach at the level of single fibres. This rate-dependent model is found to capture experimental results available in literature for single fibres with a good agreement (both quantitatively and qualitatively). Based on the identified model at the level of single fibres, the time-dependent hygro-mechanical response is upscaled towards the network scale. To this end, random model networks of ribbon shaped fibres are generated and their response is simulated. The network-scale response, emerging from the rate-dependent fibre model, demonstrates the ability to predict the response of networks subjected to relaxation at a constant moisture level. The developed numerical model predicts lower values of overall stress response in single fibres as compared to networks. Also, stress relaxation predicted by the rate-dependent model in the cross-direction of the networks is in agreement with the experimental observations by Johanson and Kubát (1967). Therefore, one of the remarkable findings of the present work is that the developed rate-dependent model is robust enough to capture the sheet scale response also qualitatively. Based on the study of these computational results, a better understanding is achieved regarding the influence of mechanical and rate-dependent properties of single fibres on the hygro-expansion of complete fibre networks, and in particular of paper sheets.
... Published works on the relationship between the macroscopic behavior of fibrous networks and micro-structural parameters address the dependence of stress transfer on the correlation length in a network (Åstrom et al., 1994); fracture of the network dominated by fibres longer than the average length (Alava and Ritala, 1990); the mechanical response of fibrous networks depending on the curl ratio (Yi et al., 2004); the magnetic and mechanical response of bonded networks of metal fibres due to filling in voids (Clyne et al., 2005); the influence of the aspect ratio and fibre concentration on the effective stiffness of planar fibre networks (Wu and Dzenis, 2005). Early attempts at structure-property relations for fibrous networks specifically addressed the mechanical response. ...
Paper is a complex material consisting of a network of cellulose _bres at the micro-level. During manufacturing, the network is dried under restraint conditions due to tension in the paper web in machine direction. This gives rise to internal strains that are stored in the produced sheet. Upon exposure to a moisture cycle, these strains may be released. This results in permanent shrinkage that may cause instabilities such as curl or waviness of the sheet. The prime objective of this paper is to model this irreversible shrinkage and to link its magnitude to the properties of the Fibres and of the network. For this purpose, randomly generated Fibrous networks of different coverages (i.e. ratio of the area occupied by fibres and that of the sheet) are modeled by means of a periodic representative volume element (RVE). Within such RVEs, a finite element method combined with a kinematic hardening plasticity model at the scale of the fibres is used to capture the irreversible response. The computational results obtained demonstrate that the magnitude of the irreversible strains increases with coverage until a certain coverage and beyond that coverage decreases in magnitude. This phenomenon is explained by considering the area fraction of free-standing fibre segments relative to bonded fibre segments in the network. A structure{property dependency of irreversible strains at the sheet-level on the micro-structural parameters of the network is thereby established.
... For example, Clyne and Markaki fabricated porous stainless steel fiber-sintered sheets via the liquid-phase sintering method with copper powder as the connecting agent. However, the tensile strength of the stainless steel fiber-sintered sheets in the porosity range of 75%-95% was no higher than 1 MPa [9][10][11]. Tang et al. fabricated stainless steel fiber felts via the solid-phase sintering method with 28 μm fibers and performed synchrotron radiation experiments to investigate the sintering mechanism and the evolution of the sintered neck, which significantly affect the mechanical strength [12,13]. ...
Porous copper fiber-sintered sheets (PCFSSs) with different porosities were fabricated through the solid-phase sintering method using cutting copper fibers. PCFSSs with the same porosity and different porosities were then joined via a fluxless soldering method. By analyzing the uniaxial tensile property of the PCFSSs, the formation mechanism of the soldered PCFSSs was investigated. The difference in the tensile properties between the soldered and original PCFSSs was examined. Experimental results indicated that, for the PCFSSs with homogeneous porosity, reducing the porosity increased the tensile strength and elongation at break significantly. The fluxless soldering method with the lead-free solder resulted in excellent joining of the PCFSSs with the same porosity and different porosities. Moreover, the final tensile strength of the soldered PCFSSs with the same porosity was nearly equal to that of their parent PCFSSs. The tensile strength of the soldered PCFSSs with different porosities depended on the higher-porosity section. After soldering the PCFSSs, Young’s modulus increased and the elongation at break reduced.
... Porous metal fiber materials have many excellent functional characteristics, such as filtration separation, energy absorption, sound absorption, efficient combustion and enhanced heat and mass transfer, and have been widely used in chemicals, textiles, medicine and electronics [1][2][3]. Generally, porous metal fiber materials are manufactured by a sintering process. The sintering process is very complex, and one or several sintering mechanisms, including evaporation-condensation (EC), surface diffusion (SD), grain boundary diffusion (GBD), volume diffusion (VD) and lattice diffusion (LD), may take place at different sintering stages [4,5]. ...
In this paper, the sintering neck growth process of metal fibers under the surface diffusion mechanism is simulated by using the Lattice Boltzmann method (LBM). The surface diffusion model is developed considering the geometrical characteristic of metal fibers. Then, the LBM scheme is constructed for solving the developed surface diffusion model. The sintering neck growth process of two metal fibers with different fiber angles is simulated by LBM. The simulated morphologies of sintering metal fibers well agree with ones obtained by experiments. Moreover, the numerical simulation results show that the sintering neck radius of two metal fibers is increased with the increase of fiber angle, which implies that the initial geometrical characteristic plays an important role in the sintering neck formation and growth of metal fibers.
... Therefore, we aim to construct a 3D fibre network reinforced composite. In terms of the fibre network, Clyne et al. have conducted a series of thorough investigations towards bonded metal fibre networks both experimentally and analytically, involving work in the characterisation of the network architecture and capture of independent elastic constants [14][15][16][17][18][19]. Some other research has also been done regarding to the mechanical properties of transversely isotropic fibre networks [20-23], such as metal fibre sintered sheet [24,25]. ...
This research stems from the idea of introducing a fibre-network structure into composites aiming to enhance the stiffness and strength of the composites. A novel new type of composites reinforced by a tranversely isotropic fibre-network in which the fibres are devided into continuous segments and randomly distributed has been proposed and found to have improved elastic properties compared to other conventional fibre or particle composites mainly due to the introduction of cross-linkers among the fibres. Combining with the effects of Poisson's ratio of the constituent materials, the fibre network composite can exhibit extraordinary stiffness. A simplified analytical model has also been proposed for comparison with the numerical results, showing close prediction of the stiffness of the fibre-network composites. Moreover, as a plate structure, the thickness of the fibre network composite is adjustable and can be tailored according to the dimensions and mechanical properties as demanded in industry.
... When the domains V i are single inclusions, the PC-W estimate statistically accounts for a part of their interactions through their spatial distribution, but the larger are the chosen representative patterns V i, the more precisely the pair interactions can be accounted for at the pattern scale. 9 As far as the considered patterns are finite sets, the estimate still regards the pair interactions between any two patterns through their spatial distribution and the dilute approximation that characterizes this estimate type still applies at the pattern 112 P. Franciosi et al. scale. Equation (11) will be enough for the following discussion purpose about the use of infinite patterns, and especially the two-phase form of it (a unique embedded phase) which simplifies to: ...
Composites comprising included phases in a continuous matrix constitute a huge class of meta-materials, whose effective properties, whether they be mechanical, physical or coupled, can be selectively optimized by using appropriate phase arrangements and architectures. An important subclass is represented by “network-reinforced matrices,” say those materials in which one or more of the embedded phases are co-continuous with the matrix in one or more directions. In this article, we present a method to study effective properties of simple such structures from which more complex ones can be accessible. Effective properties are shown, in the framework of linear elasticity, estimable by using the global mean Green operator for the entire embedded fiber network which is by definition through sample spanning. This network operator is obtained from one of infinite planar alignments of infinite fibers, which the network can be seen as an interpenetrated set of, with the fiber interactions being fully accounted for in the alignments. The mean operator of such alignments is given in exact closed form for isotropic elastic-like or dielectric-like matrices. We first exemplify how these operators relevantly provide, from classic homogenization frameworks, effective properties in the case of 1D fiber bundles embedded in an isotropic elastic-like medium. It is also shown that using infinite patterns with fully interacting elements over their whole influence range at any element concentration suppresses the dilute approximation limit of these frameworks. We finally present a construction method for a global operator of fiber networks described as interpenetrated such bundles.
... It has been applied for fibres network in [27] for stainless steel fibres, carbon fibres and glass fibres network cross-linked with epoxy. Clyne et al. [28] have also presented a simple analytical model to predict the stiffness of metallic bonded fibres. These models assume that the fibre orientation distribution of the networks is either 2D random or 3D random. ...
A method to determine the orientation and diameter distributions of mineral wool fibre networks using X-ray tomography and image analysis is presented. The method is applied to two different types of mineral wool: glass wool and stone wool. The orientation information is obtained from the computation of the structure tensor, and the diameter is estimated by applying a greyscale granulometry. The results of the image analysis indicate the two types of fibres are distributed in a 2D planar arrangement with the glass wool fibres showing a higher degree of planarity than the stone wool fibres. The orientation information is included in an analytical model based on a Euler–Bernoulli beam approximation. The model enables prediction of the transverse stiffness. It is indicated that the glass wool transverse stiffness is lower than the stone wool transverse stiffness. Comparison with experimental results confirms the assumption that the underlying deformation mechanism of mineral wool is the bending of fibre segments between bonds.
... Previous work has already analysed for this specific material simplified single-fibre geometries under magnetic actuation 15 . Or global values have been predicted analytically for fibre assemblies 41,42 . This present study investigates complete fibre network geometries and analyses the matrix strain on local level. ...
Fibre networks combined with a matrix material in their void phase make the design of novel and smart composite materials possible. Their application is of great interest in the field of advanced paper or as bioactive tissue engineering scaffolds. In the present study, we analyse the mechanical interaction between metallic fibre networks under magnetic actuation and a matrix material. Experimentally validated FE models are combined for that purpose in one joint simulation. High performance computing facilities are used. The resulting strain in the composite’s matrix is not uniform across the sample volume. Instead we show that boundary conditions and proximity to the fibre structure strongly influence the local strain magnitude. An analytical model of local strain magnitude is derived. The strain magnitude of 0.001 which is of particular interest for bone growth stimulation is achievable by this assembly. In light of these findings, the investigated composite structure is suitable for creating and for regulating contactless a stress field which is to be imposed on the matrix material. Topics for future research will be the advanced modelling of the biological components and the potential medical utilisation.
... To provide a reference for comparison, the results of the Charpy impact test for a previous study on EWMs, 15 aluminum foams, 23 and any other porous materials [24][25][26][27][28] are also presented in Table II. The entangled wire materials with lower porosities have stronger impact resistance capacity. ...
A novel stainless steel porous twisted wire material (PTWM) is made of twisted short wires by compaction followed by vacuum high-temperature solid-phase sintering. The twisted short wires are fabricated by using a self-developed rotary multicutter tool to cut stainless steel wire ropes. The PTWMs with 46–70% porosities have been investigated in terms of porous structures and Charpy impact behavior. The PTWMs with spatial composite intertexture structures exhibit interconnected open-pore microstructures with a variety of shapes and sizes. The pore size distributions became convergent with decreasing porosities. The span of pore distribution of the PTWM with a diameter of 90 μm was half than that of the PTWM with a diameter of 160 μm under 65–66% porosity. The impact toughness of the former is 2.6 times than that of the latter. By increasing the porosity from 46 to 70%, the impact toughness decreases from 17.9 to 9.1 J/cm². Macroscopically integral failure-morphologies of the PTWMs present mixed ductile–brittle failure mechanisms, but microscopic impact deformation and failure mechanisms mainly show the ductile failure and fracture of pore skeletons. The PTWMs demonstrate complex energy absorption mechanisms.
... These results are complemented by new dynamic compression tests performed on a different set of samples which are accompanied by the simulation of the deformation behavior in order to gain more insight into the governing failure mechanisms. When comparing results of different research groups, the direction of loading with regard to the morphology of the fiber structure and the nature of the inter-fiber bonds has to be taken into account very carefully as they influence results considerably, i.e., the quantification of the fiber structure anisotropy and its influence on the stiffness of the fiber network has been addressed in [3]. This work has been carried out on steel fiber structures where the connection between the fibers was made by a brazing process using copper as the braze material. ...
Rigid metallic fiber structures made from a variety of different metals and alloys have been investigated mainly with regard to their functional properties such as heat transfer, pressure drop, or filtration characteristics. With the recent advent of aluminum and magnesium-based fiber structures, the application of such structures in light-weight crash absorbers has become conceivable. The present paper therefore elucidates the mechanical behavior of rigid sintered fiber structures under quasi-static and dynamic loading. Special attention is paid to the strongly anisotropic properties observed for different directions of loading in relation to the main fiber orientation. Basically, the structures show an orthotropic behavior; however, a finite thickness of the fiber slabs results in moderate deviations from a purely orthotropic behavior. The morphology of the tested specimens is examined by computed tomography, and experimental results for different directions of loading as well as different relative densities are presented. Numerical calculations were carried out using real structural data derived from the computed tomography data. Depending on the direction of loading, the fiber structures show a distinctively different deformation behavior both experimentally and numerically. Based on these results, the prevalent modes of deformation are discussed and a first comparison with an established polymer foam and an assessment of the applicability of aluminum fiber structures in crash protection devices is attempted.
... Owing to its filtration separation, energy absorption, sound absorption, efficient combustion, enhanced heat and mass transfer, porous metal fiber materials have been widely used in the fields of electronics, chemicals, textiles, machinery, food and medicine [1][2][3]. Previously, researchers have carried out some works on the preparation and application of the porous metal fiber materials [4,5]. Tang et al. [6] studied the sound absorbing properties of stainless steel fiber porous materials and found that the sound absorption coefficient increases with the increase in porosity and thickness of fibrous materials. ...
The formation of sintering necks between two metal fibers was investigated using the oval–oval model with respect to the fiber angle range of 0°–90°. Surface diffusion was assumed to be the predominant mechanism in every section of the junction of two metal fibers in this model, which was addressed numerically using the level-set method. The growth rates of the sintering necks in the direction of the bisector of obtuse angle, the bisector of acute angle and the fiber axis were discussed in detail. It is found that the growth rate of the sintering necks decreases with fiber angle increasing in the direction of the fiber axis and the bisector of acute angle. However, an opposite variation in growth rate of sintering necks can be found in the direction of the bisector of obtuse angle. The numerical simulation results show that the growth rate of the sintering necks is significantly affected by the initial local geometrical structure which is determined by the fiber angle.
Graphical abstract
The oval–oval model based on level-set method is proposed to simulate the growth process of sintering necks between two metal fibers with respect to the fiber angle range of 0°–90°. According to the simulation results, the influences of initial local geometrical structure and the initial evolution speed on the growth rate of the sintering necks are investigated.
... Thus far, many studies have developed new fabrication methods and improved the mechanical properties of porous metals. Markaki and Clyne [14,15] produced novel porous sheets using liquid phase sintering method of short stainless steel fibers with 100 m diameter. They found that the porous sheets had a porosity varying from 75% to 95% and a tensile strength below 1 MPa. ...
A novel oriented linear porous metal (OLPM) with high porosity was fabricated through solid-sintering method with cutting copper fibers. In this study, tensile experiments were conducted to investigate the fracture process of the OLPM and the effects of porosity and sintering parameters on the tensile properties. The typical tensile stress-strain plot of this material was obtained based on a large number of tensile test results. The plot can be divided into three stages, namely, initial linear elastic stage, plastic deformation stage, and tensile fracture stage. Based on the results, the fracture mechanism of the OLPM was further studied. Moreover, the porosity and sintering parameters were also varied to investigate their influence on the tensile properties. Tensile strength and plastic deformation were found to decrease with increasing porosity ranging from 70% to 90%. A higher sintering temperature produced a higher tensile strength for the OLPM sintered in the temperature range of 700°C–900°C, but the strength decreased at 1000°C. In addition, the extension of holding time could also slightly affect the tensile strength. Finally, the tensile properties of the OLPM are significantly higher than those of commercial porous metal and porous metal fiber sintered sheet.
... This allows large deflections under low applied loads -i.e. generates a low stiffness -and this is the basis of many types of (highly compliant) fibre network material [25][26][27][28][29][30][31][32][33]. (There is, however, always the possibility of some kind of inelastic deformation occurring, as a result of plasticity or damage in the cell walls, giving an anomalously low stiffness: it is essential when measuring such stiffness to check that the deformation is genuinely reversible.) ...
Statement of significance:
The high porosity and interconnectivity of tissue engineering scaffolds result in highly compliant structures (ie large deflections under low applied loads). Characterisation is essential if these scaffolds are to be systematically optimised. Scaffold overstraining during characterisation can lead to misleading results. In this study, the stiffness (in dry and hydrated states) and specific permeability of freeze-dried collagen scaffolds have been measured using techniques customised for low stiffness structures. The scaffold cell structure is investigated using X-ray computed tomography, which has been applied previously to visualise such materials, without extracting any structural parameters or simulating fluid flow. These are carried out in this work. 2-photon confocal microscopy is used for the first time to study the structure in hydrated state.
... As the structural changes influence the aeroacoustic performance, not only the mechanical properties, but also the damage behavior is of major interest. X-ray tomography is a non-destructive tool that enables material characterization and in situ experiments to reveal structural changes and damage during mechanical tests and, therefore, it has been used in several studies [8][9][10][11][12][13]. In this study, the damage behavior is analyzed using a combination of tensile tests and three dimensional computed tomography, which allows determination of the damage location with a high resolution. ...
The reduction of aircraft noise is important due to a rising number of flights and the growth of urban centers close to airports. During landing, a significant part of the noise is generated by flow around the airframe. To reduce that noise porous trailing edges are investigated. Ideally, the porous materials should to be structural materials as well. Therefore, the mechanical properties and damage behavior are of major interest. The aim of this study is to show the change of structure and the damage behavior of sintered fiber felts, which are promising materials for porous trailing edges, under tensile loading using a combination of tensile tests and three dimensional computed tomography scans. By stopping the tensile test after a defined stress or strain and scanning the sample, it is possible to correlate structural changes and the development of damage to certain features in the stress-strain curve and follow the damage process with a high spatial resolution. Finally, the correlation between material structure and mechanical behavior is demonstrated.
... A substantial increase in impact strength, flexural strength as well as flexural modulus could be observed in case of the maleated PP. Finally, numerical and analytical evaluations of metal fiber-reinforced thermoplastic composites have been performed by SAYMAN et al. [12], ARSLAN et al. [13], and CLYNE et al. [14]. ...
The objective of the presented study was to investigate the adhesion and bonding quality between steel fibers and a polypropylene (PP) matrix. In order to improve the fiber matrix adhesion, neat PP had been modified with various proportions of maleic anhydride grafted polypropylene (MAHgPP). Fiber pull-out tests had been conducted to determine the apparent interfacial shear strength Tapp. It could be proven that the grafted PP grades exhibit up to 40 % better Tapp values than the unmodified PP matrix, while the major mechanical properties of the matrix were kept constant. Furthermore, scanning electron microscope pictures confirmed an excellent bonding quality between steel and PP grafted with 0.1% MAH.
... Une comparaison de différentes structures cellulaires, incluant les nids d'abeille et les treillis, est proposée par Wadley (2006). Un autre type de matériau d'âme en fibres métalliques enchevêtrées a été développé et étudié par Markaki et Clyne (2003), Clyne et al. (2005) et Zhou et Stronge (2005). Cependant, ce matériau d'âme est de faible épaisseur (de l'ordre de 1 mm) et de masse volumique importante du fait des fibres métalliques. ...
... As so far, some interesting research works have been conducted to develop the new fabrication methods and improve the mechanical properties of PMFSS. Clyne and Markaki [12,13] produced novel porous sheets using the liquid phase sintering of short stainless steel fibers with 100 lm diameter. They found that the porous sheets have a porosity varied from 75% to 95% and a tensile strength below 1 MPa. ...
Background
Deformation properties of porous metallic fibre networks are strongly dependent on their architecture, mainly fibre orientation, besides being a function of constituent fibre material and its geometrical parameters. Hence, it is important to comprehend and evaluate the effect of individual fibre orientation and fibre-segment aspect ratio on the mechanical properties of porous metallic fibre networks.Objective
To investigate the effect of fibre orientation on its deformation characteristics and to analytically explain the observed mechanical behaviour.Methods
Present work captures the deformation of inclined copper fibres (in the range of 0° to 45°), mounted on a novel paper-tab framework, under tensile loading. A 1D analytical model has also been developed to elucidate the inclined fibre deformation and yield characteristics.ResultsAn increase in fibre inclination angle (from 0° to 45°), exhibits a decreased yield force. The model validates the experiments, and for elastic region establishes that the axial, shear forces and bending moment increase with fibre inclination angle, where the increase in axial force is predominant. The model further establishes the effect of fibre-segment aspect ratio on the yield force of fibre networks and determines that increase in diameter of the fibres has the same effect as decrease in segment length with regards to these forces.Conclusions
The study establishes the effect of fibre inclination angle on the deformation behaviour of porous metallic fibre network materials and can potentially be used to optimise their architecture for targeted applications.
Motive Metallic fibre networks and their mechanical behaviour are only insufficiently understood. In this particular field of research, the use of nano-CT scans offers advanced opportunities for the optimised planning of experimental work and component design. Several novel applications will benefit from this research; in particular, tissue engineering applications where a controlled and reproducible mechanical stimulus on cells is required can make use of these components. Method
For the present study, the geometry of metallic fibre network samples is measured and digitalised through the use of nano-CT scan protocols and adequate radiological post-processing steps. Fibre medial axes are transferred into finite element assemblies and are exposed to magnetic actuation models. Network displacement of input geometries is quantified by averaging of node displacement fields. Key resultsComplex 3D deformation fields with regions of tension, shear, and compression are obtained. Results from a previous study about matrix material deformation can be confirmed in this study for greater sample geometries. The strain magnitude is not uniform across the samples; several influencing parameters and deformation patterns are identified. A simple analytical model can be presented which quantifies the material deformation. Conclusions
Nano-CT scans provide an efficient radiological tool in the planning of relevant experimental procedures. The present study confirms the general usability of fibre networks for the contactless creation of 3D strain fields in tissue engineering. Mechanical effects in tissue growth stimulation known from experimental work are obtained numerically for the investigated assemblies. Further work about the mechanical effects in tissue cultures appears highly worthwhile.
The Fourier–Green homogenization method for estimating the behavior of composites was first developed for aggregates and inhomogeneity-reinforced (-weakened) matrices, based on Eshelby (Proc R Soc Lond, A 421:379–396, 1957, Proc R Soc Lond, A 252:561–569, 1959) solution of the isolated inclusion problem. The need to address increasingly complex structures opened fruitful development routes, firstly solving the inhomogeneity pair interaction problem and the one of heterogeneous (double or multilayered) inhomogeneities, in order to account for inclusion dense concentrations and patterns. This work reports recent developments from the authors and co-workers which examined in that framework possibly infinite inclusion patterns, possibly arranged into an infinite network possibly co-continuous with the embedding matrix and possibly evolving under strain. The proposed modeling amounts to determining the representative mean Green operator (mGO) for the infinite pattern or network in its current (strain evolving) state. Once the method foundations being summarized, previously solved “elementary” cases are recalled, concerning infinite coaxial alignments of spheres, spheroids or finite cylinders and planar alignments of infinite parallel cylinders or rectangular beams. It is next shown how other complex patterns or networks could be represented in combining such elementary ones. The mGO solution for a new family of inhomogeneous axial inclusion alignments is reported to support the discussion. Potential other application fields are evoked.
The present study investigates the relationship between 3D microstructure and macroscopic mechanical performance of porous copper fiber sintered felt. The sintered junctions at fiber-to-fiber crossovers play an important role in the mechanical stiffness of the fiber system. Therefore, to reconstruct the fibrous network model with controllable geometry details at fiber-to-fiber sintered junctions, the fiber system is modeled using a force-based packing approach to represent fibers as chains of balls. Different levels of overlapping between fibers are modeled by varying the factor parameter controlling distance of balls at junctions of different fibers. By gradually increasing the distance parameter, the fibers in fiber mat will reach the critical state between connected (overlapped) and separated, and the critical factor value which barely keeps the integrity of geometry model was obtained. The virtual models are then used for in-plane tensile simulations using finite element method. By introducing the failure criteria, the tensile deformation process involving the tensile strength and critical elongation of fiber system is captured and compared with experimental results. The simulated data are similar to the measured data in magnitude, shape and 2% critical elongation of the stress–strain curves. Numerical analysis allows the investigation of effect of fiber junctions on mechanical strength which decreases dramatically as fiber overlapping decreases. The most approximate data appear at virtual model using the critical distance value and thus indicate a weak mechanical stiffness of the sintered junction.
We propose an estimate for the effective elastic properties of a new imagined two-phase bi-continuous composite material type with a so-called ``pantographic-inspired” (P-I) architecture in the sense of a matrix reinforcement which is a 3D fiber network capable of large, pantographic-like, deformations, owing to particular properties carried by the fiber interconnections. Such fiber networks co-continuous with the matrix are described from an assemblage of inter-penetrated planar alignments of parallel infinite, identical and equally distant, rods or beams that we call fiber layers or FPAs for ``fiber planar alignments”. Piece-wise linear deformation of such a structure is constrained, as 2D pantographs are, by the specific relations that link the evolutions of the FPA misorientations, of the fiber inter distance and concentration within each FPA, and of the given characteristics to the through-layer interconnections. We derive effective properties within a well defined first gradient elastic homogenization scheme for macro-homogeneous composite structures, based on explicating the involved mean Green operator (mGO) for the representative pattern of such a P-I networked reinforcement in an isotropic matrix. This mGO for P-I composites is built in making use of previously derived and presented mGOs for rod and beam FPAs. Comparisons with Young and shear modulus variations during numerical homogeneous extension simulations show that the proposed modeling provides relevant effective property evolutions with the advantage of being analytical. Comparing so estimated force-displacement curves with numerical ones for 2D pantographs enables to identify ways to further account in the modeling for the specific strengthening effects of the FPA interconnections in pantographs. This tends to prove such P-I composite structures, still to be manufactured, to possibly also behave similarly to pantograph ones.
This paper describes an investigation into the potential of a novel type of ceramic composite for use as Diesel Particulate Filters (DPFs). Materials for this application need to be highly permeable to gas flow, capable of filtering and retaining fine particulate and be stable under demanding thermo-mechanical conditions. Novel materials have been produced, via a conventional blending, cold pressing and sintering route, containing coarse alumina particles and/or fine alumina fibres. Several thermal and mechanical properties are measured, for a range of fibre contents. Thermal Shock Resistance (TSR) has been investigated both experimentally and via evaluation of a TSR merit index, based on a combination of properties. This type of material shows promise in terms of thermo-mechanical stability, particularly with high fibre content. There are also indications that such composites would be suitable for DPF usage in terms of permeability levels and the filtration of fine particulate.
Ce travail a été réalisé dans le cadre du projet EcOBEx, qui consiste à réduire le bruit du groupe motopropulseur rayonné à l’extérieur par l’ajout d’écrans acoustiques dans le compartiment moteur du véhicule. Les écrans acoustiques sont fabriqués par thermocompression de matériaux poreux uniformes. Les propriétés et l’épaisseur du matériau évoluent en fonction du degré de compression subit par le matériau. L’objectif de ce travail est de proposer des lois pour prédire l’évolution des propriétés des matériaux à partir du taux de compression et de leurs valeurs initiales avant compression. Dans un premier temps, on s’intéresse aux paramètres du modèle de fluide équivalent de Johnson-Champoux-Allard-Lafarge (JCAL) : porosité, résistivité au passage d’air, tortuosité, longueurs caractéristiques visqueuse et thermique, perméabilité thermique statique. Des expressions analytiques sont proposées pour prédire la variation de ces paramètres en fonction de la compression. Elles sont développées à partir d’un modèle de matériaux fibreux à fibres cylindriques où les variations d’orientation des fibres induites par la thermocompression peuvent être prises en compte. Les résultats sont en bon accord avec les mesures effectuées sur deux types de matériaux (mousse à cellules ouvertes et fibreux). Un modèle empirique généralisé est finalement proposé pour la résistivité au passage d’air. Dans un deuxième temps, on s’attache aux paramètres élastiques dont la connaissance est essentielle pour prendre en compte la vibration du squelette. La méthode expérimentale quasistatique est d’abord appliquée pour étudier l’évolution du module de Young par rapport au taux de compression pour les fibres et les mousses. Une loi de puissance est alors proposée pour prédire ces variations. Enfin, une méthode inverse pour estimer les propriétés élastiques d’un matériau poroélastique orthotrope à partir d’une mesure vibratoire d’un écran tricouche thermocomprimé est proposée. Cette méthode permet de caractériser les propriétés élastiques du matériau poreux dans une situation proche de son application réelle.
Due to the availability of commercial laboratory systems and the emergence of user facilities at synchrotron radiation sources, studies of microcomputed tomography or microCT have increased exponentially. MicroComputed Technology provides a complete introduction to the technology, describing how to use it effectively and understand its results. The first part of the book focuses on methodology, covering experimental methods, data analysis, and visualization approaches. The second part addresses various microCT applications, including porous solids, microstructural evolution, soft tissue studies, multimode studies, and indirect analyses. The author presents a sufficient amount of fundamental material so that those new to the field can develop a relative understanding of how to design their own microCT studies. One of the first full-length references dedicated to microCT, this book provides an accessible introduction to field, supplemented with application examples and color images.
There has been substantial growth in the technology of composite manufacturing using the LCM method. The RTM process was robust but was a costly affair for long composites parts due to the two sided mold requirement and also due to the number of fixture required in a RTM process. VARTM or some time also called as VI (Vacuum Infusion) is a cheap and a viable option for the big size composite parts .Vacuum infusion has improved over the last decade due to the focus and ease in operation and its ability to produce long composite parts. This has achieved a good attention of the scientist in the last decade and continues to receive the attention of the world. There are several variants of this process and most of them operate at a compaction pressure of 1 bar. There are several research groups which are involved in the advancement of this method of composite manufacturing. Some codes are now available for the simulation of the process, and some amount of automation has also been applied in this method. As in VI process one sided moulds are used and the other side covered with a plastic bag is always exposed to the atmospheric pressure, there is no solid control on the face exposed, this increases the chances of thickness variation along the length of the infusion. In the absence of proper infusion there is possibility of improper saturation leading to the dry spot formation making the composite weak at the point of dry spot. The strength of the composite manufactured by VI depends a lot on the proper design of the injection point and vents, and online control so that the preform is completely saturated with the resin before it cures. This paper investigates the evolution of this method of composite manufacturing, with the focus on the key issue of saturation of fiber in the Vacuum infusion process.
In this chapter, a brief outline is given of the potential of ferromagnetic fiber networks for usage in delivering in vivo strains to in-growing bone. Beneficial effects on bone-implant bonding can accrue from ferromagnetic fiber networks which deform in vivo via an external magnetic field of clinical magnitude applying therapeutic strains to bone filling the inter-fiber spaces. Simple analytical models based on the torque exerted on a fully-magnetized fiber in conjunction with tomographic data can be used to predict the magneto-mechanical response. In vitro cell culture data have been obtained on both 2D (fully-dense) and 3D (high porous) surfaces to identify an optimum fiber material and establish the surfaces’ ability to support the culture of human osteoblasts and mesenchymal stem cells without inducing toxic or inflammatory responses. Preliminary experimental results on magnetic actuation of ferromagnetic fiber networks suggest an actuation-mediated upregulation of specific genes in the osteogenic lineage together with an increase in protein release.
Carbon-bonded carbon fiber composites (CBCFs) were widely used as thermal insulation materials due to their light weight and ultra-low thermal conductivity. The CBCFs with density of about 0.256 g/cm³ were tested in compression with the modulus and strength evaluated. The in-plane and out-of-plane tests revealed obvious anisotropic behavior of the material, which could be attributed to the fibers distribution. The unloading-reloading tests showed more evidence for the difference of the mechanical behaviors between in-plane and out-of-plane. In addition, we presented a finite element model to predict the mechanical properties of the CBCFs, and the deformation mechanisms as well. The numerical results showed the compressive modulus and strength increased with density following exponential functions. Moreover, the effects of fiber length and the fiber orientation on the mechanical properties were also discussed numerically. The results of this paper are helpful for the design and optimization of these materials for potential applications.
By means of the experimental method, micromechanical model and Finite Element Method (FEM), this paper studied the compressive behaviors of the three-dimensional random fibrous (3D RF) material in the through-the-thickness (TTT) and in-plane (IP) directions at elevated temperatures. The compressive experiments showed that the fracture strength and Young's modulus of the 3D RF material in the TTT and IP directions decrease as increasing temperature. The specimens fracture through breaking the fibers under the bending deformation, while almost all the bonding zones keep intact. A simple micromechanical model and a FEM model are developed to simulate the mechanical properties of the 3D RF material. The micromechanical model ignores the randomness of the fibers, while in the FEM model special attention is drawn to the influence of the morphological characteristic. Numerical results from the micromechanical model and FEM model agree well with the observations from the compressive experiments.
A novel porous honeycomb-type substrate has been developed using solid-state sintering stainless steel fibers. The porous sintered stainless steel fiber honeycombs (PSSSFH) are composed of a skeleton of sintered stainless steel fibers, three-dimensionally interconnected porous structures and multiple parallel microchannels. The bending behavior of the PSSSFH is investigated using three-point bending tests. Four stages, including an elastic stage, a yielding stage with a plateau, a hardening stage and a failure stage, are observed during the bending process of the PSSSFH. In the initial yielding stage, the bending forces increase slowly with displacement increasing, and then a yielding plateau follows, which is unique compared with other porous materials. Moreover, the structure parameters of the PSSSFH are varied to investigate the influence on the bending strength. It is determined that the multiple parallel microchannels can enhance the bending strength of porous stainless steel fiber sintered substrates (PSSFSS) and do not influence the variation trend of bending strength of PSSFSS with porosity increasing. The open ratio is conducive to increasing the bending strength, and the microchannel diameters ranging from 0.5 mm to 1.5 mm have little influence on the bending strength. In addition, both the increasing of sintering temperature and sintering time can strengthen the PSSSFH.
The difference of sintering crunodes of metal powders and fibers is discussed. The mathematical model of the surface diffusion described by the difference in mean curvature is defined as a Hamilton-Jacobi-type equation, and the model is numerically solved by the level set method. The three-dimensional numerical simulations of two metal powders and fibers (the fiber angle is 0° or 90°) are implemented by this mathematical model, respectively. The numerical simulation results accord with the experimental ones. The sintering neck growth trends of metal powders and metal fibers are similar. The sintering neck radius of metal fibers is larger than that of metal powders. The difference of the neck radius is caused by the difference of geometric structure which makes an important influence on the curvature affecting the migration rate of atoms.
Sintering of layered metal fiber sheets produces a structured, tunable, paper-like material that holds promise for thermal and biomaterial applications. Particularly promising for these areas is a material system synthesized by the sequential-overlap method, which produces a networked, transversely isotropic open cell porous material. Engineering application of these materials has been limited due in part to uncertainty about their mechanical responses. Here, we present a comprehensive structural and mechanical characterization of these materials, and define a modeling framework suitable for engineering design. X-ray tomography revealed a layered structure with an isotropic fiber distribution within each layer. In-plane uniaxial compression and tension tests revealed a linear dependence of Young's modulus and yield strength upon relative fiber density. Out-of-plane tests, however, revealed much lower Young's modulus and strength, with quartic and cubic dependence upon relative density, respectively. Fiber fracture was the dominant mode of failure for tension within the “in-plane” directions of the fiber layers, and fiber decohesion was the dominant mode of failure for tension applied in the “out-of-plane” direction, normal to the layers. Models based upon dispersions of beams predicted both in-plane and out-of-plane elastoplastic properties as a function of the relative density of fibers. These models provide a foundation for mechanical design with and optimization of these materials for a broad range of potential applications.
Aerogels based on cellulose nanofibrils (CNF) have been of a great interest as absorbents due to their high absorption capacity, low density, biodegradability, and large surface area. Hydrophobic aerogels has been designed to give excellent oil absorption tendency from water. Herein, we present an in-situ method for CNF surface modification and hydrophobic aerogel preparation. Neither solvent exchange nor fluorine chemical is used in aerogel preparations. The as-prepared hydrophobic aerogels exhibit low density (23.2 mg/cm 3), high porosity (98.5%), good flexibility, and solvent-induced shape recovery property. Successful surface modification was confirmed through field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and water contact angle measurements. The hydrophobic aerogels show high absorption capacities for various oils, depending on liquid density, up to 47× their original weight but low water uptake (<0.5 g/g aerogel).
This is a review of the processing, structure and properties of metals containing a significant volume fraction of distributed internal porosity. These materials serve in a variety of applications, some of which place emphasis on their mechanical properties, while others are driven by transport processes made possible by the accessibility of open pores to the ingress and flow of fluid. Both classes of properties are reviewed after presenting the making and the structure of these materials. Coverage thus includes the processing and structure of highly porous metals, and their properties including conduction, fluid flow, convective heat and mass transfer, thermal expansion, elastic deformation, followed by plasticity, creep, fracture and fatigue.
The difference of sintering crunodes of metal powders and fibers is discussed. The mathematical model of the surface diffusion described by the difference in mean curvature is defined as a Hamilton-Jacobi-type equation, and the model is numerically solved by the level set method. The three-dimensional numerical simulations of two metal powders and fibers (the fiber angle is 0° or 90°) are implemented by this mathematical model, respectively. The numerical simulation results accord with the experimental ones. The sintering neck growth trends of metal powders and metal fibers are similar. The sintering neck radius of metal fibers is larger than that of metal powders. The difference of the neck radius is caused by the difference of geometric structure which makes an important influence on the curvature affecting the migration rate of atoms. © 2015, Central South University Press and Springer-Verlag Berlin Heidelberg.
An approach of microstructure design for random metal fibrous structure was proposed. A variety of the material's microstructures under different fabrication configurations were investigated utilizing micro-CT screening, skeleton network reconstruction, and characteristics analysis. A parametric-driven modeling algorithm was developed to address the effective description of the random fibrous network, which could be mapped with fabrication configurations. The influence of the characteristics of the complex network on fluid transport properties was investigated by CFD simulation. The results show that distribution of fibre length and angle, which is controlled by normal probability density function, is basically consistent with the data of measured samples; that fiber pore structure has enhancement effect on fluid velocity that tends to decline with increased porosity; that under the condition of same entrance velocity, pressure drop decreases with the increase of the porosity; and that the internal fluid velocity in the fibrous network tends to increase faster with a decreased variance of normal distribution. ©, 2015, Central South University of Technology. All right reserved.
Membranes were produced from fine (∼10 nm) alumina fibres, by dispersing them in liquid and using controlled sedimentation to produce two types of membrane – one a duplex structure (layers of well-dispersed fibres and micro-bundles) and the other entirely micro-bundles. Incorporation of silica, via a sol-gel route, produced “hybrid” forms. Filtration and separation efficiencies were assessed using two ionic dyes of similar molecular weight, but opposite charge. Successful separation of these is attributed to surface electrical effects within nano-pores. Hybrid duplex membranes give an excellent combination of fine scale filtration efficiency and high permeability.
A novel porous metal fiber sintered sheet (PMFSS) with high porosity was fabricated by the solid-state sintering method of copper fibers. In this study, both three-and four-point bending setup were established to characterize the bending properties of PMFSS. Similar three stages in the three-and four-point bending fracture process were observed for the PMFSS with 80% porosity sintered at 900 degrees C for 60 min. Comparing with the three-point bending, it is found that much smaller bending force was obtained in the four-point bending test under the same displacement conditions. Moreover, the porosity and sintering parameters were also varied to investigate the influence on the bending properties of PMFSS. Both three-and four-point bending strength were found to be decreased with increasing porosity ranging from 70% to 90%. Higher sintering temperature produced higher bending strength for the PMFSS sintered in the temperature range of 700-1000 degrees C. Besides, the extension of holding time also could slightly affect the bending strength. Crown Copyright
Sintered metal fibre porous felt is a new kind of functional materials with outstanding properties. Using the methods of immersion test, electrochemical polarization, metallographic and SEM analysis, the corrosion mechanism of sintered 316L stainless steel fibre porous felts was systemically studied. It is found that the intergranular and pitting corrosions both influence the corrosion process. The corrosion resistance of sintered joints between the fibres is better than that of the fibre rod; and the felt is more severely corroded and its mass increases after corrosion as its porosity increases.
This paper outlines a procedure for producing membrane materials, using a novel alumina fiber with a diameter of the order of 10 nm and a range of processing conditions. The as-received fibers had very high aspect ratios and were supplied in the form of mats in which they were unidirectionally aligned. Membranes have been produced by dispersing the fibers in a liquid, together with a binding agent, followed by sedimentation. During dispersion, the fibers tended to break up and become detached from each other. Depending on the period of dispersion, the fiber architecture in the membranes could range from a “duplex” structure containing bundles of locally aligned fibers to a more homogeneous assembly of relatively short fibers. Some samples exhibited a stratified structure, with a homogeneous layer below and a duplex structure above. Correlations have been established between these architectures and transport properties relevant to use of these membranes as fine scale filters. Measurements have been made of the specific permeability, using water as the permeating fluid. The results are consistent with predictions based on the Carmen–Kozeny equation. The filtration efficiencies of the membranes have also been assessed, using two dyes with different molecular weights. This performance was found to be consistent with filtration taking place primarily by simple mechanical entrapment of the dye molecules. Relevant mechanical properties of the membranes have also been measured, notably the stiffness (Young's modulus) and the tensile strength. These results are briefly considered in terms of implications for the durability of the membranes as filters. It is concluded that these membranes, perhaps particularly those with duplex or layered structures, offer considerable promise as ultra-fine scale filters.
Mechanical properties of open-cellular magnesium alloys with three types of geometric cell-structures, that is, a random round cell-structure (type A), a controlled diamond cell-structure for which the angle between the struts and the load direction is 45 degree (type B) and a controlled square cell-structure for which the angle between the struts and the loading direction is 0 degree (90 degree) (type C), are investigated by compressive tests. Results indicate that type C showed a higher collapse stress than the other two types. The collapse mechanism and the effects of the loading direction on collapse stress for the three types of magnesium alloys are discussed from the viewpoint of bending, buckling and yielding of the struts. It is suggested that collapse for the open-cellular magnesium alloys is associated with yielding of struts.
This article relates to the fabrication of metal-matrix composites by the injection of liquid metal into a fibrous preform
under an applied pressure. An analysis is presented describing the elastic deformation, fracture behavior, and melt infiltration
characteristics of an assembly of fibers in an approximately planar random array. The predictions of a finite difference model
describing the heat flow and solidification in the system are also examined. The predictions from the modeling are found to
be broadly consistent with various types of experimental observation made with aluminum-based melts and fine δ alumina fibers.
A number of microstructural features are examined and several recommendations put forward concerning optimization of microstructurevia control of processing parameters.
Three variants of a novel steel sandwich sheet material have been studied. The geometrical arrangements of the steel fibres in the core have been characterised. Certain mechanical properties of the fibres have also been investigated. The beam stiffnesses of the sheets, and also their through-thickness Young's moduli, have been measured. These results have been compared with model predictions. It is shown that the beam stiffnesses are in all cases significantly lower than expected from simple bending theory. This is attributed to the low through-thickness stiffness of the core and also to a low resistance to shear. Modelling of these properties has facilitated the identification of changes to the core structure, which should lead to improved beam stiffness, while retaining a low density. Increased fibre diameter, and possibly an alteration to the fibre sectional shape, are the most promising changes. Of course, implications for other properties, and for ease of manufacture, will also need to be borne in mind.
Cellular solids include engineering honeycombs and foams (which can now be made from polymers, metals, ceramics, and composites) as well as natural materials, such as wood, cork, and cancellous bone. This new edition of a classic work details current understanding of the structure and mechanical behavior of cellular materials, and the ways in which they can be exploited in engineering design. Gibson and Ashby have brought the book completely up to date, including new work on processing of metallic and ceramic foams and on the mechanical, electrical and acoustic properties of cellular solids. Data for commercially available foams are presented on material property charts; two new case studies show how the charts are used for selection of foams in engineering design. Over 150 references appearing in the literature since the publication of the first edition are cited. It will be of interest to graduate students and researchers in materials science and engineering.
Solid networks made by inducing interconnection at fibre contact points in an assembly of fibres usually present a high elastic anisotropy. The paper aims at elucidating the dependence of the stiffness matrix of a random planar fibre network on fibre volume fraction Vf and out-of-plane fibre orientation ψ. A periodic model is designed for representing the network architecture. Bounds for the elastic constants are obtained by calculating volume weighted averages of the elastic properties for periodic networks characterised by a uniform distribution of in-plane fibre orientations. Predictions are derived for the dependence of the in-plane Young’s modulus, out-of-plane Young’s modulus, and in-plane shear modulus on Vf and ψ. The model is assessed by reference to experimental results for a network of metallic fibres. The underestimation of experimental results is presumed to be due to the fact that the model does not account for the effect of triangulation.
Cellular solids include engineering honeycombs and foams (which can now be made from polymers, metals, ceramics, and composites) as well as natural materials, such as wood, cork, and cancellous bone. This new edition of a classic work details current understanding of the structure and mechanical behavior of cellular materials, and the ways in which they can be exploited in engineering design. Gibson and Ashby have brought the book completely up to date, including new work on processing of metallic and ceramic foams and on the mechanical, electrical and acoustic properties of cellular solids. Data for commercially available foams are presented on material property charts; two new case studies show how the charts are used for selection of foams in engineering design. Over 150 references appearing in the literature since the publication of the first edition are cited. It will be of interest to graduate students and researchers in materials science and engineering. © Lorna J. Gibson and Michael F. Ashby, 1988 and Lorna J. Gibson and Michael F. Ashby, 1997.
Strongly bonded assemblies of metallic fibres constitute an interesting class of highly porous, permeable materials. A high degree of control can be exercised over their properties, by tailoring the fibre architecture so as to achieve specified void contents, fibre connectivity and fibre orientation distributions. There is also scope for introducing controlled heterogeneity and gradient structures. It is possible, by using relatively strong fibres, and generating appropriate fibre–fibre joint geometries, to produce material with relatively high tensile strength and toughness, facilitating usage in various load-bearing applications. Furthermore, if ferromagnetic fibres are employed, then the material can be actuated by the imposition of a magnetic field, with the fibres becoming magnetised along their length and tending to align parallel with the applied field. The resultant deformation of the fibre array generates a shape change, which can be predicted for a given fibre orientation distribution and fibre segment aspect ratio (inter-joint distance over fibre diameter). Moreover, a non-magnetic (matrix) material located in the inter-fibre space will be mechanically strained by these fibre deflections. This was proposed in a previous publication as a possible mechanism for bone growth stimulation by magnetic field application, for example by making the surface layers of a prosthetic implant from a ferromagnetic fibre array, into which bone cell growth would occur. In the present paper, analyses are presented for prediction both of conventional elastic constants exhibited by bonded fibre arrays and of novel magneto-mechanical elastic constants. These analyses also allow identification of conditions for the onset of inelastic behaviour. Comparisons are made with experimental data, relating to nominally isotropic fibre arrays, with and without the presence of relatively compliant matrices. It is confirmed that a simple modelling approach can give fairly reliable indications of how the material will behave, under both mechanical and magnetic loading.
A procedure is outlined for the production of highly porous material by liquid phase sintering of short stainless steel fibres, about 100 μm in diameter. The fibres, which were produced by a melt extraction route, were first electroplated with copper to a thickness of a few μm. The sintering procedure was then completed by holding at about 1100 °C for a few minutes. It is shown that this operation generates strong joints by the migration of liquid copper to the fibre–fibre contact regions, as a result of capillary action. A preliminary study of the mechanical behaviour material produced in this way indicates that its toughness is relatively high, for a highly porous metallic material, and that its fracture energy is broadly consistent with predictions from a model based on evaluation of the work done by plastic deformation and rupture of individual fibres close to the fracture plane.
The mechanical properties of cellular materials such as polymeric, ceramic, and metallic foams were analyzed. The primary quantity controlling the properties was the apparent density of the cellular material. The strength, stiffness and energy absorption efficiency of structures with constant apparent density was found to vary independently by variations in the microarchitecture. Strength and stiffness were correlated with each other not only for varying apparent density but also for varying microarchitecture.
The architecture of bonded fibre networks produced by sintering of short stainless steel fibres has been characterised using computed X-ray microtomography. Two important characteristics of such networks are the distributions of fibre segment length and fibre orientation. These have strong influences on the mechanical, thermal and electrical properties. To extract quantitative architectural data from the reconstructed fibre networks, a 3-D skeletonisation algorithm was used to convert the reconstructed fibre surfaces into their corresponding medial axes.
The principle of the tomography technique and the different possible set-ups, which can be used to obtain medium-(10 μm) and high-(1 μm) resolution, three-dimensional, non-destructive images, are shown in this paper. Illustrations are made of the applications of the technique in the field of materials science. Examples are given for medium-resolution images of metallic foams and model metal matrix composites that are reinforced with spherical particles. High-resolution examples are shown for aluminium alloys. For low-absorbent materials we show that the phase contrast obtained using synchrotron radiation can provide a valuable solution. The quantitative use of these images, coupled with in-situ tensile tests or used for the simple analysis of the initial microstructure of several structural materials, is also described.
The mechanical properties of metal fibre porous structures were studied in the light of their potential application as surface
coatings of implants. Stainless steel AISI 316 L fibres with diameters of 50 and 100μm were compacted and sintered. The variation
of the modulus of elasticity with density, as obtained in tension, corresponds closely with theoretical models. The ultimate
failure of the tensile specimens proceeds through the fibres, and not through the sinter bonds, except at lower densities.
Differences in yield strength between 50 and 100 μm fibre tensile specimens are explained on the basis of the onset of plastic
deformation of the individual fibres. Upon compression the modulus of elasticity is nearly 10 times smaller than in tension.
This result is due to the different deformation patterns of the fibres in compression and tension.
The development of different manufacturing techniques for foams, most especially metallic foams have opened a new market of opportunities for multifunctional cellular metallic materials. However, it is yet unclear how to quantitatively characterise the microstructure and internal architecture of foams precisely. In this paper, the potential of using micro-computed tomography in characterising the morphometric parameters of foams are explored. 3D morphometric parameters of different types of closed cell aluminium alloy foam have been characterised, and the effects of the measurement resolution, and the integration time on the measured morphometric parameters have been studied. The model based and model independent morphometric parameters are comparable with measurements using other characterisation techniques. We conclude that the new generations of micro-computed tomography equipment have versatile capability for a non-invasive and -destructive characterisation of foams.
This study concerns three variants of a novel type of thin sandwich sheet. Details of the core structures, and also the results of an investigation into elastic properties, were presented in the first part of this pair of papers. A study was also made of the tensile properties of single fibres of the type present in the core of these sheets. In this second paper, an investigation is presented of the resistance offered by these materials to delamination of the two faceplates. In one variant of the material, in which the fibres lie approximately normal to the plane of the sheet, delamination occurs predominantly by frictional pull-out of fibres from their sockets in the adhesive. The mode I fracture energy has been measured at about 340 J m−2. This value is consistent with predictions from a model based on shear-lag theory, with a fibre–adhesive interfacial shear strength of about 5 MPa. It is noted that there should be scope for improving the fracture energy somewhat by raising the strength of the fibre–adhesive bond. For the other two variants studied, in which the fibres are softer (as a result of heat treatment during sintering) and are inclined close to the plane of the sheet, the measured fracture energy is appreciably lower at about 30 J m−2. In this case, delamination occurs by fracture of the fibres near the mid-plane. Application of a simple model for prediction of the fracture energy in this case leads to the conclusion that some of the fracture was probably of sintered necks between fibres, rather than the fibres themselves, and that this process required considerably less energy.
A brief experimental and theoretical study is presented into the elastic deformation of bonded arrays of ferromagnetic fibres, when subjected to an external magnetic field. Material made of such fibre arrays is of potential interest for certain biomedical applications, such as prosthetic implants. Externally imposed magnetic fields could be used to generate mechanical strains in surrounding tissue, with possible physiological benefits. It is shown that it should be possible to generate strains within embryonic bone cell networks, forming within such a fibre array, which are sufficient to stimulate enhanced growth. The effects outlined here could thus form the basis of surgical or therapeutic advances.
Elastic properties of cellular metals processed by sintering mats of fibres
- F Delannay
- T W Clyne
Delannay F, Clyne TW. Elastic properties of cellular metals
processed by sintering mats of fibres. In: Banhart J et al., editors.
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