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Mechanics of thin ultra-light stainless steel sandwich sheet material: Part II. Resistance to delamination
Abstract
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.
... It exhibits a number of unique properties such as high specific strength, high specific toughness, high specific surface area, and high permeability. As a result, it is widely used for filtration [1], lightweight sandwich core structures [2,3], fuel cell electrodes [4], biomedical devices [5,6], catalyst supports [7], heat transfer elements [8], and environmental noise control devices [9]. ...
... As a kind of ultralight cellular material, their mechanical properties need to be fully understood. In earlier times, most studies focused on the relationships between mechanical properties and structural variables such as relative density and fiber orientation [2,3,[10][11][12][13]. Zhao et al. [10] investigated the constitutive relationship between the shear modulus and relative density of sintered 316L SSFFs. ...
... Zhao et al. [10] investigated the constitutive relationship between the shear modulus and relative density of sintered 316L SSFFs. Markaki et al. [2,3,12] established the single fiber deformation model for sintered SSFF and captured the network structure (e.g., fiber orientation distribution, inter-joint distance) by computed X-ray tomography, then applied the data to a model for prediction of the Young's modulus [11]. By contrast, only little attention was paid to the effect of such microstructures like the sintering joint and fiber ...
To optimize the tensile properties of sintered 316L stainless steel fiber felts (SSFFs) which is important for their practical applications, the influence of sintering conditions on the microstructure (fiber ligament, sintering joint) and in turn, the tensile properties was investigated experimentally. It was shown that the tensile strength and tensile elongation of SSFFs were dominated by the tensile properties of the fiber ligaments and the bonding strength of the sintering joints. With the increase of sintering temperature versus holding time, the tensile strength of the fiber ligaments dropped significantly, while the sintering joints grew, producing a higher bonding strength between the fibers, resulting in more fibers being involved in the tensile process. These changes in sintering joints and fiberligamentsfinallyledtoarelativelystaticultimatestrengthofSSFFswithasignificantlyincreased elongation, thus with a large increase in tensile fracture energy. The increase of size of the sintering joints also helped to considerably raise the tensile fatigue limit of 316L SSFFs. This research provides a basis to improve the mechanical properties of sintered 316L SSFFs in industrial production.
... It exhibits a number of unique properties such as high specific strength, high specific toughness, high specific surface area, and high permeability. As a result, it is widely used for filtration [1], lightweight sandwich core structures [2,3], fuel cell electrodes [4], biomedical devices [5,6], catalyst supports [7], heat transfer elements [8], and environmental noise control devices [9]. ...
... As a kind of ultralight cellular material, their mechanical properties need to be fully understood. In earlier times, most studies focused on the relationships between mechanical properties and structural variables such as relative density and fiber orientation [2,3,[10][11][12][13]. Zhao et al. [10] investigated the constitutive relationship between the shear modulus and relative density of sintered 316L SSFFs. ...
... Zhao et al. [10] investigated the constitutive relationship between the shear modulus and relative density of sintered 316L SSFFs. Markaki et al. [2,3,12] established the single fiber deformation model for sintered SSFF and captured the network structure (e.g., fiber orientation distribution, inter-joint distance) by computed X-ray tomography, then applied the data to a model for prediction of the Young's modulus [11]. By contrast, only little attention was paid to the effect of such microstructures like the sintering joint and fiber ...
To optimize the tensile properties of sintered 316L stainless steel fiber felts (SSFFs) which is important for their practical applications, the influence of sintering conditions on the microstructure (fiber ligament, sintering joint) and in turn, the tensile properties was investigated experimentally. It was shown that the tensile strength and tensile elongation of SSFFs were dominated by the tensile properties of the fiber ligaments and the bonding strength of the sintering joints. With the increase of sintering temperature versus holding time, the tensile strength of the fiber ligaments dropped significantly, while the sintering joints grew, producing a higher bonding strength between the fibers, resulting in more fibers being involved in the tensile process. These changes in sintering joints and fiber ligaments finally led to a relatively static ultimate strength of SSFFs with a significantly increased elongation, thus with a large increase in tensile fracture energy. The increase of size of the sintering joints also helped to considerably raise the tensile fatigue limit of 316L SSFFs. This research provides a basis to improve the mechanical properties of sintered 316L SSFFs in industrial production.
... There have been several previous experimental studies of the mechanical response of stochastic metallic fibre networks made of Cu [4], Ti [5], 20%Cr-80%Ni [6], steel [7][8][9] and stainless steel [10][11][12][13][14][15][16][17][18][19][20][21][22] fibres (in particular 304 [10,11], 316L [12][13][14][15][16][17][18] and 446 [19][20][21][22]). The majority of these studies focused on the effect of fibre size and volume fraction on tensile [4,6,[10][11][12][13][14]17,19], compressive [5,7,13,17,18,[20][21][22], torsional [8,17] and impact [9] responses. ...
... There have been several previous experimental studies of the mechanical response of stochastic metallic fibre networks made of Cu [4], Ti [5], 20%Cr-80%Ni [6], steel [7][8][9] and stainless steel [10][11][12][13][14][15][16][17][18][19][20][21][22] fibres (in particular 304 [10,11], 316L [12][13][14][15][16][17][18] and 446 [19][20][21][22]). The majority of these studies focused on the effect of fibre size and volume fraction on tensile [4,6,[10][11][12][13][14]17,19], compressive [5,7,13,17,18,[20][21][22], torsional [8,17] and impact [9] responses. ...
... Acknowledging that some gross simplifications are being incorporated here, the estimated fracture area was approximately five times larger than the cross-sectional area (based on nominal dimensions). Fracture energy values were found to increase with fibre volume fraction in an approximately linear fashion, which is in agreement with a previously developed analytical model [16]. The aforementioned model [16] predicts the fracture energy G fr for this type of fibrous material, based on the work of fracture of a single fibre, assuming that all fibres fracture. ...
In the present paper, highly porous fibre networks made of 316L fibres, with different fibre volume fractions, are characterized in terms of network architecture, elastic constants and fracture energies. Elastic constants are measured using quasi-static mechanical and modal vibration testing, yielding local and globally averaged properties, respectively. Differences between quasi-static and dynamic elastic constants are attributed to through-thickness shear effects. Regardless of the method employed, networks show signs of material inhomogeneity at high fibre densities, in agreement with X-ray nanotomography results. Strong auxetic (or negative Poisson’s ratio) behaviour is observed in the through-thickness direction, which is attributed to fibre kinking induced during processing. Measured fracture energies are compared with model predictions incorporating information about in-plane fibre orientation distribution, fibre volume fraction and single fibre work of fracture. Experimental values are broadly consistent with model predictions, based on the assumption that this energy is primarily associated with plastic deformation of individual fibres within a process zone of the same order as the inter-joint spacing.
... doi:10.1016/j.actamat.2004. 10.037 mechanical efficiency of various strut assemblies, such as trusses, and design techniques for the creation of high flexural rigidities, etc., have been well-known to mechanical engineers for a very long time, but clear translation of such concepts into the design of highly porous materials is not so advanced. ...
... There have been several previous studies of the mechanical characteristics of bonded fibre arrays [7][8][9][10][11][12][13]. The work of Gibson and Ashby concerned with modelling of open cell foams [14,15] can be applied to fibre arrays (see Section 3.1.2). ...
... Theoretical study [17,18] of the compressive failure of such materials has usually led to the conclusion that local yielding, followed by plastic buckling of struts, is the critical process. A model has been developed by Markaki and Clyne [10] for the tensile fracture energy of bonded fibre arrays, utilising experimental data for the failure characteristics of single fibres. ...
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.
... One of the drawbacks of these materials is its expensive manufacturing cost. Recently, a new type of sandwich was developed from bonded metallic fibres as core material [13][14][15][16][17][18][19]. ...
... Bonded metallic fibres present attractive combination of properties like high specific stiffness, good damping capacity and energy absorption. Metal fibres are bonded with a polymeric adhesive [15,16] or fabricated in a mat-like form and consolidated by solid state sintering [20]. Entangled fibres were cross-linked by epoxy spraying under air flow to be used as core material [29][30][31]. ...
Entangled cross-linked fibres were studied for an application as core material for sandwich structures. Specimens were produced from carbon, aramid and glass fibres, and cross-links were achieved using epoxy spraying. It was observed that this type of entangled cross-linked fibres could be fabricated without any major technical difficulties. The scope of this paper is to study the effect of some different parameters on the mechanical properties of these materials. Different effects were investigated: effect of fibres length, of fibres nature, of mixing fibres, of carbon skins and of the resin. The first part of this paper deals with the production of these entangled cross-linked fibres. The compression, tension and three point bending tests are detailed in the second part and the results are compared with usual core material currently used in industries.
... Entangled cross-linked fibres present a strong interest in highly porous metals for a wide range of applications [5][6][7][8][9][10][11]. They present a relatively low density, a high porosity and a simplicity of production thanks to its cost-effective routes with considerable versatility as far as type of fibres and architecture are concerned. ...
... They present a relatively low density, a high porosity and a simplicity of production thanks to its cost-effective routes with considerable versatility as far as type of fibres and architecture are concerned. Entangled cross-linked fibres can be made by assembling a set of metallic fibres and bonding them together by different processes such as welding, brazing, sintering or adhesive bonding [9,12,13]. Recently, a new type of entangled cross-linked fibres was developed based on entangled carbon, aramid and glass fibres bonded by epoxy vaporization [5,[14][15][16]. This material has the potential to exhibit an attractive combination of properties for sandwich application, such as an open porosity, multifunctional properties or the possibility to obtain complex shapes [5]. ...
Entangled cross-linked carbon, aramid and glass fibres were recently produced by epoxy spraying for an application as core material for sandwich panel. The Young’s moduli in compression and tension have been previously measured and briefly summarized in this paper. To optimize the core structure, modelling of these properties has been achieved in the present paper. The cross-link fibres have a random orientation and the stiffness of the epoxy joint is modelled by a torsion spring. A parallel model is chosen for homogenisation. It was found that the experimentally estimated stiffness of these materials fits fairly well with the modelled ones.
... The nature of the contacts is also a parameter which influences the properties of entangled materials; indeed, it is possible to create permanent and non-permanent contacts. Processes to make entangled materials can be simple, and their use has recently been studied as a core material for sandwich structures [1][2][3][4][5]. Indeed, they present an alternative to foams (metal or polymer), the use of which can be limited due to weldability issues or the addition of functions. ...
... steel, foams are difficult to process because of the high melting point, and the use of steel fibers is simpler. This is why many studies have been performed on these materials, testing their mechanical properties (compression, tension, bending), thermal and electrical conductivity, and also damp-ing properties [4][5][6][7][8][9][10][11][12]. To predict the properties of materials made of entangled fibers, analytical and numerical modeling has been developed. ...
Entangled materials can be manufactured using fibers made from various materials, such as carbon, glass or steel. The mechanical properties of these low-density materials are linked to their architecture (fiber orientation, number of contacts, etc.). Specimens can be produced with and without cross-links between fibers by sintering for steel wool or by using epoxy spraying for carbon or glass fibers. Experimental mechanical compression tests were performed on these materials. The results were analyzed taking into account the architecture thanks to the relationships existing between morphological data and macroscopic mechanical behavior.
... It is also possible to make an estimate of the expected fracture energy for this type of fibrous material. A previously-developed model [8,15] for deformation and rupture of a sintered fibre array of this type, based on the physical model depicted in Fig. 10, led to the following expression for the fracture energy (in J m À2 ) ...
... Schematic depiction of the model[8,15] used for prediction of energy absorption during fibre deformation and fracture. ...
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.
... Core material is usually in the form of honeycomb, foam, or balsa. Recently, a novel type of sandwich has been developed with bonded metallic fibers as core material [10][11][12][13][14][15]. This material presents an attractive combination of properties like high specific stiffness, good damping capacity, and energy absorption. ...
... Glass fibers are widely used, because of their low cost, in many applications like thermal insulation for pipe, building. Bonded metal fiber network are used as core material [10][11][12][13][14][15]. The purpose of the present study is to analyze and to model the mechanical behavior of materials made from these three types of fibers with and without cross-link. ...
Entangled fibrous materials have been manufactured from different fibers: metallic fibers, glass fibers, and carbon fibers. Specimens have been produced with and without cross links between fibers. Cross-links have been achieved using epoxy spraying. The scope of this article is to analyze the mechanical behavior of these materials and to compare it with available models. The first part of this article deals with entangled fibrous materials without crosslink between fibers. Compression tests are detailed and test reproducibility is checked. In the second part, compression tests were performed on materials manufactured with cross-linked fibers. The specific mechanical behavior obtained is discussed.
... The base fibers can be flexibly selected to meet various needs, which are made of copper [1], titanium [2], carbon nanotube [3][4][5][6][7], and steel [8]. In particular, a number of stainless steel fibers [9][10][11][12][13][14][15][16] exhibit superior performance such as high temperature resistance, corrosion resistance, high surface to mass ratio and permeability. As the cell size can be accurately controlled with different fibers of diameter ranging from several to several hundred micrometers, they are widely applied in filtration and separation [17], gas infiltration [18], catalyst support [19], biomaterials [11,15], heat transfer [20], and sound absorption [10,21,22]. ...
Sintered metal fiber sheets (MFSs) made by sequential-overlap method are transversely isotropic open-cell cellular materials with paper-like fiber network architectures, which exhibit auxeticity and are promising for various potential applications due to the reentrant micro-structure. The thickness effect on the out-of-plane auxeticity (negative Poisson's ratio) of MFSs samples of 2–20 mm thick subjected to in-plane tensile loading is investigated with digital image correlation technique. Furthermore, the deformation modes of fibers within MFSs during various loading stages are examined with X-ray tomography. It is found that in addition to the straightening of reentrant fibers, fiber layers with defects and joints failure induced slippage between adjacent layers leads to local shear and results in unique umbrella-like local deformation termed umbrella effect, which gradually dominates the auxeticity during tensile loading. Although remarkably increasing lateral deformation, the umbrella effect significantly diminishes the in-plane mechanical performance such as rigidity and strength. In particular, this effect is suppressed by sample thickness: the overall performance tends to stabilize with sample thickness greater than a certain value, provided that the MFS is uniform with all fibers randomly distributed. The finding facilitates wider application of auxetic MFSs with further understanding on the relationship between the thickness effect and performance.
... Cambridge is a sintered mat where the fibres are mainly oriented at an acute angle to the faceplates. In Hybrix® the core is bonded to the faceplates by epoxy or resin bonding (as a continuous layer or discreet blobs), whilst the core of the Cambridge sandwich panels is bonded by brazing or adhesive [111,112]. In both materials, both core and faceplates are usually made of stainless steel. ...
Incremental sheet forming (ISF) is a flexible process where an indenter moves over the surface of a sheet of metal to form a 3D shell incrementally by a progression of localised deformation. Despite extensive research into the process, the deformation mechanics is not fully understood. This thesis presents new insights into the mechanics of ISF applied to two groups of materials: sheet metals and sandwich panels. A new system for measuring tool forces in ISF is commissioned. The system uses six loadcells to measure reaction forces on the workpiece frame. Each force signal has an uncertainty of ±15 N. This is likely to be small in comparison to tool forces measured in ISF. The mechanics of ISF of sheet metals is researched. Through-thickness deformation and strains of copper plates are measured for single-point incremental forming (SPIF) and two-point incremental forming (TPIF). It is shown that the deformation mechanisms of SPIF and TPIF are shear parallel to the tool direction, with both shear and stretching perpendicular to the tool direction. Tool forces are measured and compared throughout the two processes. Tool forces follow similar trends to strains, suggesting that shear parallel to the tool direction is a result of friction between the tool and workpiece. The mechanics of ISF of sandwich panels is investigated. The mechanical viability of applying ISF to various sandwich panel designs is evaluated by observing failure modes and damage under two simple tool paths. ISF is applicable to metal/polymer/metal sandwich panels. This is because the cores and faceplates are ductile and largely incompressible, and therefore survive local indentation during ISF without collapse. Through-thickness deformation, tool forces and applicability of the sine law for prediction of wall thickness are measured and compared for a metal/polymer/metal sandwich panel and a monolithic sheet metal. The mechanical results for ISF of sheet metals transfer closely to sandwich panels. Hence, established knowledge and process implementation procedures derived for ISF of monolithic sheet metals may be used in the future for ISF of sandwich panels.
... However, it has been shown that certain types of fibrous networks, do exhibit promising strength and toughness levels. [6][7][8] These networks were first proposed as implant materials in the late 1960s. 9 Although some work has been done on the inflammatory and cytotoxic responses to titanium [10][11][12][13][14][15][16] and 316L 17 fiber networks, we are the first to report on 444. ...
The aim of the current work was to examine the human monocyte response to 444 ferritic stainless steel fibre networks. 316L austenitic fibre networks, of the same fibre volume fraction, were used as control surfaces. Fluorescence and scanning electron microscopies suggest that the cells exhibited a good degree of attachment and penetration throughout both networks. Lactate Dehydrogenase (LDH) and TNF-α releases were used as indicators of cytotoxicity and inflammatory responses respectively. LDH release indicated similar levels of monocyte viability when in contact with the 444 and 316L fibre networks. Both networks elicited a low level secretion of TNF-α, which was significantly lower than that of the positive control wells containing zymosan. Collectively, the results suggest that 444 ferritic and 316L austenitic networks induced similar cytotoxic and inflammatory responses from human monocytes.
... 있다. (3,4) s ...
A new thin sandwich panel composed of an aluminum expanded metal core adhesively jointed with stainless steel face sheets is introduced, and its mechanical behavior under three-point bending is investigated. The strength and stiffness are analyzed theoretically, and the press-formability and strength enhancement are evaluated experimentally. The specimens with the specific configurations exhibit face yielding well before face-core separation, which means that the sandwich panel can be formed by a press without failure. The measured load levels corresponding to the face yielding and the face-core separation agree fairly well with the theoretical estimations. For a given weight, the sandwich panel is superior to a solid panel in terms of strength, stiffness, and press-formability.
... And the spatial orientation of each fiber can be represented more detailed as: u 1 ¼ ðÀ cos w cos h; À cos w sin h; sin wÞ u 2 ¼ ðcos w cos h; cos w sin h; sin wÞ u 3 ¼ ðcos w cos h; À cos w sin h; À sin wÞ u 4 ¼ ðÀ cos w cos h; cos w sin h; À sin wÞ ð2Þ 2.1.2. Bilinear simplification for mechanical properties In order to simplify the modeling process and improve calculation efficiency, bilinear assumption is still needed to predict the mechanical properties of single fiber and whole SSSFF [21]. (1) In microscopic view, the stress-stain curve of metal fiber is assumed to be bilinear. ...
Sintered stainless steel fiber felt (SSSFF) is a type of cellular material promising for functional and structural applications due to high porosity, controllable permeability, and high specific surface area, etc. In this study, a micromechanics elastic–plastic constitutive model was proposed for accurate representation of material behavior of SSSFF. Firstly, microscopic geometric structure was investigated and representative volume element (RVE) was established according to the reasonable simplifications and assumptions. Secondly, fundamental equations of elastic theory including equilibrium equations and geometric equations were built. Principle of virtual work and generalized Hook’s law were applied to obtain the elastic behavior. The incremental theory was adopted to derive the plastic stress–strain relations. Thirdly, the elastic and plastic relations were unified by statistical theory considering the fiber length and fiber orientation distribution. Finally, four SSSFF materials were introduced as numerical examples and the numerical results show good agreements with experimental results. The proposed micromechanics constitutive model, also expected to be applicable to other metal fiber sintered materials, is beneficial to predict the mechanical properties of sintered fiber materials and guide the material design.
... Recent advances in cellular theory [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] and manufacturing techniques [21,22] have created an interest in developing new applications for foam materials in the fabrication of lightweight engineering components [23]. Specifically, metallic foams provide several advantages to the designer due to their diverse multifunctional characteristics and ductility [21,24,25]. ...
A new and innovative concept is proposed for designing lightweight fan blades for aircraft engines using commercially available 17-4PH precipitation hardened stainless steel. Rotating fan blades in aircraft engines experience a complex loading state consisting of combinations of centrifugal, distributed pressure and torsional loads. Theoretical failure plastic collapse maps, showing plots of the foam relative density versus face sheet thickness, t, normalized by the fan blade span length, L, have been generated for rectangular 17-4PH sandwiched foam panels under these three loading modes assuming three failure plastic collapse modes. These maps show that the 17-4PH sandwiched foam panels can fail by either the yielding of the face sheets, yielding of the foam core or wrinkling of the face sheets depending on foam relative density, the magnitude of t/L and the loading mode. The design envelop of a generic fan blade is superimposed on the maps to provide valuable insights on the probable failure modes in a sandwiched foam fan blade.
... 15) have also been employed as cores in lightweight sandwich panels, fabricated entirely from stainless steel. The basic mechanics of these panels have been studied previously [12,[20][21][22], as have their resistance welding characteristics [23]. The present study is focussed on their behaviour under projectile impact, which has not been previously addressed. ...
This paper concerns energy absorption during projectile penetration of thin, lightweight sandwich panels with metallic fibre cores. The panels were made entirely of austenitic stainless steel (grade 304). The faceplates were 0.4mm thick and the core (∼1–2mm thick) was a random assembly of metallic fibres, consolidated by solid state sintering. The impact tests were simulated using ABAQUS. Faceplate behaviour was modelled using the Johnson and Cook plasticity relation and a strain rate-dependent, critical plastic strain failure criterion. The core was modelled as an anisotropic, compressible continuum, with failure based on a quadratic, shear stress-based criterion. The experimental data show that, with increasing impact velocity, the absorbed energy decreased from the ballistic limit, reached a minimum value, and then underwent a monotonic increase. The FEM modelling demonstrates that this increase arises from the kinetic energy of ejected fragments, while the energy absorbed by plastic deformation and fracture tends to a plateau. Normalised absorbed energies have been compared to values for single faceplates. The sandwich panels are marginally superior to single plates on an areal density basis.
... However, it has been shown that certain types of fibrous networks, do exhibit promising strength and toughness levels. [6][7][8] These networks were first proposed as implant materials in the late 1960s. 9 Although some work has been done on the inflammatory and cytotoxic responses to titanium [10][11][12][13][14][15][16] and 316L 17 fiber networks, we are the first to report on 444. ...
Beneficial effects on bone-implant bonding may accrue from ferromagnetic fiber networks on implants which can deform in vivo inducing controlled levels of mechanical strain directly in growing bone. This approach requires ferromagnetic fibers that can be implanted in vivo without stimulating undue inflammatory cell responses or cytotoxicity. This study examines the short-term in vitro responses, including attachment, viability, and inflammatory stimulation, of human peripheral blood monocytes to 444 ferritic stainless steel fiber networks. Two types of 444 networks, differing in fiber cross section and thus surface area, were considered alongside austenitic stainless steel fiber networks, made of 316L, a widely established implant material. Similar high percent seeding efficiencies were measured by CyQuant® on all fiber networks after 48 h of cell culture. Extensive cell attachment was confirmed by fluorescence and scanning electron microscopy, which showed round monocytes attached at various depths into the fiber networks. Medium concentrations of lactate dehydrogenase (LDH) and tumor necrosis factor alpha (TNF-α) were determined as indicators of viability and inflammatory responses, respectively. Percent LDH concentrations were similar for both 444 fiber networks at all time points, whereas significantly lower than those of 316L control networks at 24 h. All networks elicited low-level secretions of TNF-α, which were significantly lower than that of the positive control wells containing zymosan. Collectively, the results indicate that 444 networks produce comparable responses to medical implant grade 316L networks and are able to support human peripheral blood monocytes in short-term in vitro cultures without inducing significant inflammatory or cytotoxic effects. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2012.
... This is illustrated in Figure 7. The concept was introduced by Markaki and Clyne, [17] and is here extended to incorporate factors such as anisotropy. The fracture energy can be expressed as where N is the number of fibres per unit sectional area and U s is the single fibre work of fracture, in units of J m -1 . ...
A study was conducted to analyze the thermo-mechanical stability of grade 304 fiber network materials at high temperature and high velocity gas streams. Thermal cycling was performed in a plasma spray facility, where the plasma gun power (15 kW) was used to generate a plasma plume of similar temperature and gas flow velocity. The tests were completed in an inert (Ar) atmosphere to minimize oxidation. Tensile tests were conducted using an ESH servo-hydraulic testing machine. The tensile force was measured using a 10 kN load cell. Mechanical testing was conducted on a Schenk screw-driven desktop testing machine. The isothermal testing aimed to investigate thermal ageing effects, when exposed to increased temperatures for extended periods of time. Results show that fiber networks retain their mechanical integrity and shape in any environment successfully.
... There is increasing interest [6,[10][11][12][13][14] in materials made by bonding together slender metallic members, such as fibres, wires, rods, ribbons etc. This can be done by brazing, sintering, welding or adhesive bonding. ...
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.
... Traditional core materials are usually honeycomb, foam or balsa. Recently, a novel type of sandwich has been developed with bonded metallic fibers as core material [39] [40] [41]. This material presents attractive combination of properties like high specific stiffness, good damping capacity and energy absorption. ...
The aim is to study the impact toughness of two types of entangled sandwich materials (heavy and light) with the help of vibration testing. A simple case of symmetrical impacts is studied in this article as no literature is available regarding impact tests on entangled sandwich materials. The variation of modal parameters with two levels of damage (BVID and Damage not apparent on the surface) is studied. Vibration test results show that the light entangled specimens possessing good damping capabilities seem more sensitive to impact damage than the heavy ones. Furthermore, damping is found to be more sensitive to damage than the stiffness variations, so it is reasonable to assume that damping may be used instead of natural frequency as a damage indicator tool for structural health monitoring purposes.
... Furthermore, the overall thickness of the sheet ($1 mm), and certain features of its core structure, are such that its processing characteristics (both formability and weldability) are comparable with those of conventional monolithic metallic sheets [3]. While some work has recently been published on the flexural stiffness [4] and interfacial delamination behavior [5] of this novel material, its tensile properties are yet to be studied. In some applications, it may be necessary to introduce holes or notches for fastening, and these can cause a severe drop in the load-bearing capability of the component. ...
The unnotched and notched tensile properties of flocked and brazed stainless steel sandwiches with fibrous cores were examined. The tensile stress-strain responses show that the fibres do not carry any load in the flocked sheets and that the load transfer is better facilitated in the brazed sandwich sheets. Notched strength results show that the flocked sheets are n otch-in sensitive whereas the brazed sheet's strength is highly sensitive to short notches. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
... These materials possess low relative density, high porosity and are cost-effective. Recently, a novel type of sandwich has been developed with bonded metallic fibers as core material [44] [45] [46] [47] [48]. This material presents attractive combination of properties like high specific stiffness, good damping capacity and energy absorption. ...
The aim of this paper is the fabrication and mechanical testing of entangled sandwich beam specimens and the comparison of their results with standard sandwich specimens with honeycomb and foam as core materials. The entangled sandwich specimens have glass fiber cores and glass woven fabric as skin materials. The tested glass fiber entangled sandwich beams possess low compressive and shear modulus as compared to honeycomb and foam sandwich beams of the same specifications. Although the entangled sandwich beams are heavier than the honeycomb and foam sandwich beams, the vibration tests show that the entangled sandwich beams possess higher damping ratios and low vibratory levels as compared to honeycomb and foam sandwich beams, making them suitable for vibro-acoustic applications where structural strength is of secondary importance, e.g., internal paneling of a helicopter.
... In addition to the limited work on fracture of ceramic reinforced with steel fibres, there have been studies of fibre network materials , oriented towards acoustic damping [37], heat exchangers [38], cores of lightweight panels [39] and bioactive layers on prosthetic implants [40]. There has also been tomographic characterisation of fibre orientation distributions [41] and use of the fibre work of fracture (per unit length) to obtain network fracture energies [42] [43]. ...
A model is presented for prediction of the fracture energy of ceramic–matrix composites containing dispersed metallic fibres. It is assumed that the work of fracture comes entirely from pull-out and/or plastic deformation of fibres bridging the crack plane. Comparisons are presented between these predictions and experimental measurements made on a commercially-available composite material of this type, containing stainless steel (304) fibres in a matrix predominantly comprising alumina and alumino-silicate phases. Good agreement is observed, and it’s noted that there is scope for the fracture energy levels to be high (∼20 kJ m−2). Higher toughness levels are both predicted and observed for coarser fibres, up to a practical limit for the fibre diameter of the order of 0.5 mm. Other deductions are also made concerning strategies for optimisation of the toughness of this type of material.
... There is current interest [1][2][3][4][5][6][7][8][9] in materials made by bonding together slender metallic members, such as fibres, wires, rods, ribbons etc. This can be done by welding, brazing, sintering or adhesive bonding. ...
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.
... This layer is highly porous, being composed of a network of ferromagnetic fibres bonded together. In addition to the capacity to provide space for cellular, vascular and bone in-growth, metal fibre networks of this type have good mechanical properties, including fracture toughness, even at high porosity levels [23,24]. During the early phase of in-growth, with a suitable micro-scale design, such material will deform elastically in response to the application of a magnetic field, in such a way as to impose tailored mechanical strains on in-growing bone tissue. ...
... Différents matériaux d'âme sont couramment utilisés pour les panneaux sandwich. Si les coeurs des premiers panneaux étaient en balsa, de nombreux matériaux cellulaires artificiels lui sont maintenant préférés, que cela soit des mousses organiques ou métalliques, des nids d'abeille (NA) ou plus récemment des structures 3D architecturées, comme des treillis [1][2][3][4][5]. Ces dernières présentent l'intérêt d'être ventilées, évitant ainsi la condensation de la vapeur d'eau dans les cellules du coeur. ...
Des matériaux à architecture poreuse et aléatoire sont élaborés à partir de fibres de verre ou de carbone enchevêtrées en vue d’une application potentielle comme âme de panneaux sandwich ventilée. Le comportement en compression des fibres simplement enchevêtrées est étudié et comparé aux modèles existants. Dans une seconde partie, les essais sont réalisés sur le matériau dans lequel les contacts sont bloqués par collage à la résine époxy. Les résultats sont ensuite analysés.
... Si les coeurs poreux ventilés et architecturés présentent des propriétés mécaniques remarquables, que les brins soient collés ou bien brasés entre eux, leur coût reste élevé. Récemment un nouveau type de matériau a été développé à partir de fibres enchevêtrées réticulées [6][7][8][9][10]. ...
Des matériaux à architecture poreuse et aléatoire ont été élaborés à partir de fibres de verre ou de carbone enchevêtrées en vue d'une application potentielle comme âme de panneaux sandwich ventilé. Les fibres de carbone ont été choisies pour leurs bonnes propriétés mécanique et les fibres de verre pour leur faible coût. Les contacts entre fibres sont bloqués par collage à la résine époxy. Un moyen d'élaboration original a été développé. Les fibres sont placées dans une enceinte et sont enchevêtrées par un flux d'air comprimée. La résine est vaporisée en fin de mélange. Les comportements en compression et traction ont été étudiés sur les deux types de fibres alors que seuls les matériaux élaborés à partir des fibres de carbone ont été étudiées en flexion 3 points.
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.
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.
Recently, weight reduction of vehicles has been of great interest, and consequently the use of composite materials in the automotive industry is increasing every year. Composite sandwich panels which consist of two skins and core materials are replacing steels in automotive floor and door. The substitution of one material for another is accompanied by change of joining method, so that adhesive bonding has been popularly used for joining method of composite materials. In the case of adhesive bonding of composite materials, there could be loss in the joint strength by delamination of two faceplates or cracking on faceplate. Thus, it is necessary to prevent loss in the joint strength by designing the joint geometry. In the present paper, adhesive bonding of aluminum sandwich sheet was tried. For understanding joint behavior, studies on stresses in the single lap joint were reviewed and failure modes of composite material were analyzed. Strength tests on the single lap joint consisting of aluminum sandwich sheet and steel were performed and variation of the joint strength with the joint configuration was shown, Based on these results, design guide of adhesive bonding in aluminum sandwich sheet was suggested.
Metal fiber sintered sheets (MFSSs) are a type of layered open cell porous materials and are transversely isotropic. Their stress-strain responses to uniaxial tension and compression and simple shear loading in different directions (i.e., in the in-plane and transverse directions) were measured. A set of characteristic stress and strain was defined and employed to formulate an elastoplastic constitutive model for the infinitesimal deformation of MFSSs subject to monotonic proportional loading. The elastoplastic potential in the constitutive model was calibrated with the measured stress-strain responses in terms of the defined characteristic stress and strain, without a need to know the yield surface and its evolution a priori. A successful application of the developed model to the multiaxial mechanical responses of MFSSs was demonstrated.
The aim of this work is to improve bone-implant bonding. This can, potentially, be achieved through the use of an implant coating composed of fibre networks. It is hypothesised that such an implant can achieve strong peri-prosthetic bone anchorage, when seeded with human mesenchymal stem cells (hMSCs). The materials employed were 444 and 316L stainless steel fibre networks of the same fibre volume fraction. The present work confirms that hMSCs are able to proliferate and differentiate towards the osteogenic lineage when seeded onto the fibre networks. Cellular viability, proliferation and metabolic activity were assessed and the results suggest higher proliferation rates when hMSC are seeded onto the 444 networks as compared to 316L. Cell distribution was found uniform across the seeded surfaces with 444 showing a somewhat higher infiltration depth.
The effects of three types of defect (i.e., two micro defects—broken fibers and separation of fiber joints and one macro defect—crack) on the mechanical properties of porous metal fiber sintered sheets (MFSSs) are investigated by a combination of numerical simulation, analytical modeling, and experimental test. All numerical simulations are based upon the previously developed micromechanics perfect random beam model. Broken fibers are realized by removing cell edges (i.e., fibers between two joints) in an otherwise perfect model. Their induced decreases in the elastic moduli and strengths are found to be much lower than those of two dimensional (2D) foams and Kagome grids. For the defect in the form of separation of fiber joints, both analytical and numerical models are developed. The predicted linear decreases in the moduli and strengths (except for the compressive strength) with increasing number of separated fiber joints indicate that MFSSs be insensitive to the defect of joint separation. To explore the effect of crack, fracture toughness of MFSSs is measured and is found to be significantly higher than that of metal foams of the same relative density (i.e., volume fraction of the constituent solid material). The underlying ductile mechanism of MFSSs is further investigated by numerical simulations, showing that plastic deformation spread all over the fibers in ligament rather than concentrate around crack tip. This study shows that MFSSs are superior in view of their resistance to the considered micro-defects and crack.
A new type of mesoscale periodic cellular material was developed by electrodepositing a high strength nanocrystalline nickel sleeve over a rapid prototyped acrylic photopolymer template. Mechanical properties of the hybrid-PCM, strength and stiffness, were measured in compression. For the thickest sleeves there was approximately a twenty times increase in the strength and stiffness of the trusses compared to the as-received polymer truss. Based on the mechanical properties of the constituent materials available analytical models were extended to predict the properties of the composite polymer-Ni PCM. The strength was predicted accurately based on the critical inelastic buckling stress of an individual strut. Scanning electron microscopy of truss samples revealed that that irreversible damage (failure of the nano-Ni sleeve over some of the face-sheet struts) began to occur only after the peak stress was reached. This observation was confirmed by the absence of small load drops in the pre-peak region of the stress-strain curve which are characteristic of cracking. In addition to the improved strength and stiffness due to the electrodeposited nano-Ni, the linear property scaling relationship characteristic of PCMs was observed for both strength and stiffness as a function of density.
Porous metal fiber sintered sheets (MFSSs) are a type of layered transversely isotropic open cell materials with low relative density (i.e., volume fraction of fibers), high specific stiffness and strength, and controllable precision for functional and structural applications. Based on a non-contact optical full field strain measurement system, the in-plane and transverse shear properties of SMFFs with relative densities ranging from 15% to 34% are investigated. For the in-plane shear, the modulus and strength are found to depend linearly upon the relative density. The associated deformation is mainly due to fiber stretching, accompanied by the direction change of metal fibers. When the shear loading is applied in the transverse direction, the deformation of the material is mainly owing to fiber bending, followed by the separation failure of the fiber joints. Measured results show that the transverse shear modulus and strength have quartic and cubic dependence upon the relative density respectively and are much lower than their in-plane counterparts. Simple micromechanics models are proposed for the in-plane and transverse moduli and strengths of MFSSs in shear. The predicted relationships between the shear mechanical properties of MFSSs and their relative density are obtained and are in good agreement with the measured ones.
Properties of entangled materials, made of fibers, depend on the number and the nature of contacts between fibers and fibers orientation. Nonsintered and sintered steel wools have been characterized by x-ray tomography to extract structural information such as fibers orientation and number of contacts before and during compression. Image analysis techniques were developed on tomography images and validated on virtual materials, generated and deformed by numerical simulation based on molecular dynamic equations. The structural parameters measured during the structural characterization were finally used to link the structure of the studied material with the measured mechanical properties. To do this link, an analytical model usually used for this kind of material was modified to describe the evolution of mechanical properties in compression.
Current developments show that in the field of sheeting alternative material concepts are successfully applied. In this context metal plastic sandwiches, which are composed of two thin metallic surface layers and a polymer core, represent an interesting group of semi-finished products. Compared to conventional sheet metal materials the structural modification caused by sandwich design provides an increased specific flexural rigidity. Extensive experimental and numerical investigations were carried out for the characterisation of this still young group of semi-finished products. The evaluation of suitable calculation methods represents a crucial step to a broad application of semi-finished metal plastic sandwiches within bulk production processes.
Porous metal fiber sintered sheets (MFSSs) are a type of low density cellular materials promising for functional and structural applications. A micromechanics random beam model is proposed to investigate the elasto-plastic behavior of MFSSs. The relative density dependence of the elastic constants and yield strength of MFSSs is predicted and found to agree well with available experimental results. Fiber stretching is identified as the dominant deformation mechanism under uniaxial and multiaxial loading. When compared with two-dimensional Voronoi foams and honeycombs, the stretching deformation dominated MFSSs exhibit higher stiffness and tensile strength, but lower compressive strength due to long fiber buckling. With the developed micromechanics model, the multiaxial elasto-plastic responses of MFSSs are simulated. A macroscopic phenomenological constitutive model with a segmented yield function is proposed to describe the predicted multiaxial responses. The yield function and its evolution can be fully calibrated in terms of the uniaxial tension and compression responses rather than complex multiaxial loading responses, which can greatly facilitate practical applications of the model. This constitutive model is also expected to be applicable to other fiber sintered materials with hydrostatic pressure sensitive and asymmetric tension–compression yielding behaviors.
Applications of sandwich panels as 3D shells are limited by the high costs of tooling required for conventional forming operations. This paper presents an investigation into whether incremental sheet forming (ISF) would be mechanically feasible alternative means to form sandwich panels. Process feasibility is assessed through examination of failure modes, thinning and surface quality after application of ISF to various sandwich panel designs. It is shown that ISF can be applied to sandwich panels which have ductile and largely incompressible cores. For a formable sandwich panel, the influence of ISF on the panel and a metal sheet of comparable plastic bending moment were evaluated. Similar trends in tool forces were observed, the sine law had similar accuracy in predicting thinning and the through-thickness deformation was similar for both materials. It is shown that 3D sandwich shells with aluminium foam cores can be produced by using ISF to form a precursor expandable material and that ISF can be used to form impressions on one surface of metal foam core sandwich panels. Failure mode maps are proposed as a future means to represent the boundaries of safe forming regions.
The mechanical behavior of ideal truss lattice materials is controlled by the so-called direct action mechanism at the microscale which involves the uniform stretching and compressing of individual truss members. Standard homogenization techniques have been employed to develop a general micromechanics-based finite-strain constitutive model for truss lattice materials. Furthermore, a specialized small-strain plasticity model has been derived. Both models have been implemented in a finite-element program and used to simulate the anisotropic plastic behavior of the octet-truss lattice material in various applications including cyclic uniaxial loading, pure shear, and three-point bending. The constitutive model predictions agree well with the results obtained from discrete finite element models. Regarding the plasticity of the octet-truss lattice material, it has been found that the elastic domain is constrained by twelve pairwise parallel hyperplanes in the six-dimensional stress space. Moreover, the mechanism-based small-strain formulation reveals that the direction of plastic flow is normal to the pressure-dependent macroscopic yield surfaces.
A sandwich material, based on a pair of thin stainless steel faceplates separated by a core incorporating stainless steel fibres, has recently been developed. This material has the potential to exhibit an attractive combination of properties, while retaining formability and general handling characteristics similar to those of conventional steel sheet. Two different core structures have been investigated: (a) transversely-aligned fibres bonded to the faceplates by adhesive and (b) a 3-dimensional network of fibres brazed to each other, and also to the faceplates. The beam stiffnesses of these sheets, and also their through-thickness Young's moduli, have been measured and compared with theoretical predictions.
Fibrous core sandwich panels are thin, lightweight structures with face sheets separated by an irregular arrangement of independent fibres; the fibres have a random angle of fibre inclination and a range of initial curvatures. These panels have small thickness so that they can be pressed into 3D curvature in a forming operation. This paper analyses the effects of core morphology on the through-thickness elastic moduli, compressive strength and the through-thickness shear strength of the fibrous core. For a specific panel construction, analytical results are compared with both Finite Element analysis and experiment. A new approach to measure the through-thickness shear modulus of fibrous core is described.
This paper deals with the design of thin, all-metal sandwich sheets for forming applications. Draw bending experiments have been performed on thin prototype sandwich materials with metallic cores of 10% relative density. The experimental results reveal core shear failure as the dominant failure mechanism. Detailed finite element analysis has been carried out to gain further insight in the mechanics of bending and unbending of sandwich sheets. Based on theoretical analysis, design maps have been constructed describing the required core shear strength as a function of the face sheet properties as well as the sandwich core thickness and the draw radius. Furthermore, the relationship between shear strength and relative density has been determined for perforated sandwich core materials. The main result of this study is that the shear strength of formable sandwich sheets should be at least one order of magnitude higher than that of most commercial cellular solids. Here, perforated sandwich cores of relative densities above 25% are suggested to prevent sandwich sheets from core shear failure in forming operations.
Entangled steel wire (Q195F) with total porosity of 36.3 ± 1.3 to 61.8 ± 2.4% and pore sizes of 15–825 µm have been investigated in terms of the porous morphologies, impact deformation and failure behavior. The results reveal that the impact toughness increases with the decrease of the porosity. The sintered entangled steel wire materials with 61.8 ± 2.4% porosity exhibit an average of 11.8 J/cm2 impact toughness. With 36.3 ± 1.3% porosity, the sintered materials have an average of 45.5 J/cm2 impact toughness. Impact absorbing energy and impact toughness have been obtained by Charpy impact testing. Essential impact deformation and failure mechanisms such as pore edges (i.e. fibers) bending, bulking, rotating, yielding, densification and fracture, as well as break (or avulsion) of sintering points in the steel wire framework contribute to the excellent energy-absorbing characteristics under impact loading condition.
Sintered steel wire mesh materials with total porosities of 36.3–61.8%, which are subjected to torsion loading, have been investigated in terms of deformation mode and failure mechanism. The experiments reveal that the twisted wire’s stretching, moving and rotating are main deformation mode, which leads to most of wires orientating towards the torsion direction. The failure occurs when the oriented wires fracture continuously, and leave behind a 45° fracture surface. The shear strength and shear modulus of the tested wire mesh samples are evaluated in the range of 44–103 MPa and 47–718 MPa, respectively. With an increase in porosity both the shear strength and the shear modulus decrease.
Obra de referencia sobre materiales de construcción, orientada al diseño y las técnicas arquitectónicas contemporáneas, de manera que el diseñador pueda seleccionar la mejor opción. La primera parte revisa cómo se han usado los diversos materiales y cómo ha cambiado este uso a través de los tiempos; la segunda, se centra en las propiedades, comportamiento, orígenes y usos en el diseño de cinco familias de materiales: metales, polímeros, cerámica y materiales compuestos y naturales; la última está dedicada a las nuevas técnicas en diseño e ingeniería.
Fibers networks materials have been elaborated from different fibers: metallic fibers, glass fibers and carbon fibers. Cross-links have been achieved using epoxy spraying. The scope of this paper is to analyze the mechanical behavior of these materials and to compare it with available models. The first part of this paper deals with elaboration of fibers network materials. In the second part, compression tests are performed. The specific mechanical behavior obtained is discussed.
The aim is the fabrication and mechanical testing of sandwich structures including a new core material known as fiber network sandwich materials. As fabrication norms for such a material do not exist as such, so the primary goal is to reproduce successfully fiber network sandwich specimens. Enhanced vibration testing diagnoses the quality of the fabrication process. These sandwich materials possess low structural strength as proved by the static tests (compression, bending), but the vibration test results give high damping values, making the material suitable for vibro-acoustic applications where structural strength is of secondary importance e.g., internal panelling of a helicopter.
A special test fixture has been developed for fracture mechanical testing of brittle materials inside an environmental scanning electron microscope. The fixture loads a double cantilever beam specimen with pure bending moments and provides stable crack growth. Crack growth is detected by in situ observation and acoustic emission. As an example, crack growth in a cubic-phase yttria-stabilized zirconia is detected easily by in situ observation of the crack-tip region. Many fracture toughness measurements are obtained for each specimen, giving high confidence in the measured fracture toughness value. In situ observation is useful for the study of toughening mechanisms and subcritical crack-growth behavior and to sort out erroneous measurements (e.g., due to crack branching).
Two current theories [11, 17] of interfacial debonding and fibre pull-out, which have been developed on the basis of fracture mechanics and shear strength criteria, respectively, are critically compared with experimental results of several composite systems. From the plots of partial debond stress,
d
p
, as a function of debond length, three different cases of the interfacial debond process can be identified, i.e. totally unstable, partially stable and totally stable. The stability of the debond process is governed not only by elastic constants, relative volume of fibre and matrix but more importantly by the nature of bonding at the interface and embedded fibre length,L. It is found that for the epoxy-based matrix composite systems, Gaoet al.'s model [17] predicts the trend of maximum debond stress,
d
*
, very well for longL, but it always overestimates
d
*
for very shortL. In contrast, Hsueh's model [11] has the capability to predict
d
*
for shortL, but it often needs significant adjustment to the bond shear strength for a better fit of the experimental results for longL. For a ceramic-based matrix composite,
d
*
predicted by the two models agree exceptionally well with experiment over almost the whole range ofL, a reflection that the assumed stable debond process in theory is actually achieved in practice. With respect to the initial frictional pull-out stress, f, the agreement between the two theories and experiments is excellent for all range ofL and all composite systems, suggesting that the solutions for f proposed by the two models are essentially identical. Although Gaoet al.'s model has the advantage to determine accurately the important interfacial properties such as residual clamping stress,q
o, and coefficient of friction, , it needs some modifications if accurate predictions of
d
*
are sought for very shortL. These include varying interfacial fracture toughness,G
ic with debond crack growth, unstable debonding for very shortL and inclusion of shear deformation in the matrix for the evaluation ofG
ic and fibre stress distribution. Hsueh's model may also be improved to obtain a better solution by including the effect of matrix axial stress existing at the debonded region on the frictionless debond stress, o.
For the first time, the load versus extension trace generated by the single-fibre pull-out test is thoroughly interpreted and mathematically modelled. The single-fibre pull-out test is employed experimentally to model the failure of fibre-reinforced composite materials. The interpretation of this model, however, varies between laboratories. In this paper, the test methodologies and the experimental and mathematical interpretations of various scientists are presented and discussed, as is some preliminary work employing optical fibres embedded in various neat resins. Also, a more complete description of the experimental events is presented and described mathematically via the critical strain energy release rate for crack initiation and propagation, the interfacial shear stress of the bond and the coefficient of friction.
Interfacial debonding and fibre pull-out stresses. Part I—critical comparison of existing theories with experiments
- Kim Jk
- Baillie C Mai
- Yw
Kim JK, Baillie C, Mai YW. Interfacial debonding and fibre pull-out stresses. Part I—critical comparison of existing theories with experiments. J. Mat. Sci. 1992;27:3143–54.
Cambridge solid state science series. Cambridge: Cambridge Univer-sity Press
- Clarke Dr S Suresh
- Ward
- Im
In: Clarke DR, Suresh S, Ward IM, editors. Cambridge solid state science series. Cambridge: Cambridge Univer-sity Press; 1996.