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The mechanical behaviour of porous austenitic stainless steel fibre structures
Abstract
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.
... 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. ...
... 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. Optimization of their performance clearly requires an understanding of the interplay between processing conditions, network architecture, fibre microstructure and mechanical response characteristics under various types of applied load. ...
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.
... 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]. ...
... 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]. In addition, it has been shown that auxetic fiber networks can have various promising mechanical properties over traditional open-cell cellular materials in terms of high specific stiffness and strength, high shear and indentation resistance [13,[23][24][25], larger fracture toughness [26] and enhanced energy absorption properties [27], among others. ...
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.
... The mechanics of metallic [1] and non-metallic [2] fibre networks have since long been the subject of research studies. One possible way to categorize the available studies is by the specific material which is investigated. ...
... The mechanics of sintered, metallic fibre networks as used for the present study have been investigated by [1,[30][31][32][33][34][35]. In [36], an architectural characterization of the six network samples of the present study was published, together with experimentally obtained mechanical properties. ...
Background:
The finite element method has complimented research in the field of network mechanics in the past years in numerous studies about various materials. Numerical predictions and the planning efficiency of experimental procedures are two of the motivational aspects for these numerical studies. The widespread availability of high performance computing facilities has been the enabler for the simulation of sufficiently large systems.
Objectives and motivation:
In the present study, finite element models were built for sintered, metallic fibre networks and validated by previously published experimental stiffness measurements. The validated models were the basis for predictions about so far unknown properties.
Materials and methods:
The finite element models were built by transferring previously published skeletons of fibre networks into finite element models. Beam theory was applied as simplification method.
Results and conclusions:
The obtained material stiffness isn't a constant but rather a function of variables such as sample size and boundary conditions. Beam theory offers an efficient finite element method for the simulated fibre networks. The experimental results can be approximated by the simulated systems. Two worthwhile aspects for future work will be the influence of size and shape and the mechanical interaction with matrix materials.
... Current material processing methods enable the tailoring of such materials for very specific applications. For instance, by choosing a suitable constituent metal fiber, MFSSs can be designed to have superior mechanical and physical properties for different application purposes, such as good resistance to corrosion, heat insulation, vibration reduction and great performance in filtration [5][6][7]. ...
... The elastic constants and yield strength of austenitic stainless steel fiber networks of relative density 4 40% and fibers diameter4 50 μm for the purpose of surface coatings of implants, were studied by Ducheyne et al. [5]. Recent advances in fiber-pullout techniques allowed measuring the elastoplastic and delamination properties of MFSSs with lower relative densities and smaller fiber diameters [8][9][10][11][12]. ...
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.
... 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). ...
... There have also been several studies of the strength and toughness of bonded fibre arrays, both in tension and under compression. Ducheyne et al. [8] measured the (tensile) strength of sintered stainless steel fibre mats to be several tens of MPa. 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. ...
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.
... Furthermore, in many cases they can readily be joined, for example by sintering, diffusion bonding or welding. There has been some work on material produced in this way-for example, Ducheyne et al. [5,6] produced material with porosity levels between 30 and 60% by sintering austenitic stainless steel wires, under compression. There are, however, very few reported studies of highly porous ($ 80-95% porosity) material being made in this way and, while some work has been done [7,8] on the elastic properties of such material, there is in general little or no information available about strength levels or other mechanical characteristics of such material. ...
... There are very few data with which this can be compared. Ducheyne et al. [5] reported considerably higher strength values for their sintered fibre materials, but the porosity levels were much lower and no meaningful comparison is possible. There have been some reports [1,4] of aluminium-based foams exhibiting similar, and even slightly higher, values, but these are usually for closed cell foams with rather lower porosity levels. ...
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.
... Kostornov et al. [5] studied the strength properties of 20%Cr-80%Ni alloy fiber materials subjected to tensile tests at room and elevated (up to 1300 K) temperatures. Ducheyne et al. [6] investigated the tensile and compressive properties of a kind of porous austenitic stainless steel fiber structure. The tensile, shear and compressive mechanical properties of MFSS, as the core of CAMBOSS and CAMBRASS (two kinds of steel sandwich sheets), were measured by Markaki and Clyne [7]. ...
The compressive mechanical properties of the sintered sheets of continuous stainless steel fibers with different fiber diameters (8 µm, 12 µm, 28 µm) are investigated at temperatures from 298 K to 1073 K. The stress-strain curves of metal fiber sintered sheet (MFSS) are obtained by testing under uniaxial compression and 0.2% offset yield stress are determined. Inner micro-structures of the material are revealed by using scanning electron microscope (SEM) and microscopic computer tomography. The results indicates that fabrication technique and porosity are two principle factors affecting the yield strength of MFSS and the strength of MFSS is insensitive to the temperature below 873 K while softening occurs at temperature 1073 K. At relative high porosity (e.g. 77%), the material with small diameter fibers tends to have higher yield strength while at low porosity, MFSS's yield strength becomes high with the increase of the fiber diameter, which is probably attributed to the joint size, the surface appearance of fibers and prehardening generated during the manufacturing of MFSS. A simplified structure model taking joint size into consideration is established to explain the influence of the joint size on the yield strength of MFSS.
... Zhao et al. [5] studied in-plane and transverse shear properties of MFSSs. Ducheyne et al. [6] investigated the tensile and compressive properties of porous austenitic stainless AIS 316L fiber material in experiment and theory. Kurgan [7,8] and Wang [9] revealed how the porosity, sintering temperature and environment influence the microstructure and mechanical properties of stainless steel P/M material, and built a model for the relationship between compressive strength and porosity. ...
Powder metallurgy (P/M) technique is usually used for manufacturing porous metal materials. However, some P/M materials are limitedly used in engineering for their performance deficiency. A novel 304 stainless steel P/M material was produced by a solid-state sintering of 304 stainless steel powders and 304 short stainless steel fibers, which were alternately laid in layers according to mass ratio. In this paper, the compressive properties of the P/M materials were characterized by a series of uniaxial compression tests. The effects of fiber content, compaction pressure and high temperature nitriding on compressive properties were investigated. The results indicated that, without nitriding, the samples changed from cuboid to cydariform without damage in the process of compression. The compressive stress was enhanced with increasing fiber content ranging from 0 to 8 wt.%. For compaction pressure from 55 to 75 MPa, greater compaction pressure improved compressive stress. Moreover, high temperature nitriding was able to significantly improve the yield stress, but collapse failure eventually occurred.
... 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.
... ANDERSEN et al [15,16] fabricated sintered metal fiber structures using aluminum-based fibers and reported their mechanical properties. DUCHEYNE et al [17] looked into the tensile and compressive properties of novel low-porosity PMFSS made from AISI316L stainless steel fibers with diameter of 50 and 100 μm. LIU et al [18,19] made a porous steel wire mesh with open pores by using metallurgical methods and assessed the effects of forming pressure and sintering parameters on the porous structure and mechanical behavior of the wire mesh. ...
A novel porous metal fiber sintered sheet (PMFSS) with a three-dimensional reticulated structure was fabricated by multi-tooth cutting and high-temperature solid-phase sintering process with copper fibers. A uniaxial tensile test was conducted to investigate the effect of fiber length and natural aging factor on the tensile properties of the PMFSS. Results indicated that, under given stress, the increase of fiber length helped reinforce the tensile strength. The elongation of the PMFSS with medium length fiber of 15 mm exhibited the optimal performance, reaching about 13.5%. After natural aging treatment for a month, the tensile strength of PMFSS significantly decreased, but the change of elongation was negligible except for the one with the shortest fiber length of 5 mm, whose elongation was effectively improved. The morphological fracture features of PMFSSs were also characterized.
... Entangled materials can be made from natural materials (wool, cotton, etc.) as well as from artificial ones (steel wool, glass wool, etc.). Bonded metal entangled cross-linked fibres offer advantages [17][18][19][20][21][22][23][24][25][26][27][28] for use like heat exchanger [26], insulation [27] or noise reduction [28]. They present a relatively low density, a high porosity and a simple production process thanks to cost-effective routes, with considerable versatility concerning metal composition and network architecture. ...
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.
... Markaki et al. [12] prepared highly porous material by liquid phase sintering of short stainless steel fibers and the tensile strength was less than 1 MPa. Ducheyne et al. [13] fabricated porous material with low porosity ranging from 20% to 58% by sintering 316L stainless steel fiber. The tensile strength of the SSSFFs made of 100 í µí¼m diameter fibers with 57.3% porosity is 52 MPa. ...
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.
... Many studies have been carried out on the mechanical characteristics of bonded fibre arrays [12,14,[17][18][19][20]. Gibson and Ashby works concerned with modelling of open cell foams. ...
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.
... An important issue in this context is that high porosity is expected to lead to reductions in mechanical properties. Depending on the fibre volume fraction, the network architecture (isotropic or highly-oriented), the fibre segment aspect ratio, experimentally measured Young's moduli values are no higher than a few GPa (15)(16)(17)(18)(19). ...
Ferromagnetic fiber networks have the potential to deform in vivo imparting therapeutic levels of strain on in-growing periprosthetic bone tissue. 444 Ferritic stainless steel provides a suitable material for this application due to its ability to support cultures of human osteoblasts (HObs) without eliciting undue inflammatory responses from monocytes in vitro. In the present article, a 444 fiber network, containing 17 vol% fibers, has been investigated. The network architecture was obtained by applying a skeletonization algorithm to three-dimensional tomographic reconstructions of the fiber networks. Elastic properties were measured using low-frequency vibration testing, providing globally averaged properties as opposed to mechanical methods that yield only local properties. The optimal region for transduction of strain to cells lies between the ferromagnetic fibers. However, cell attachment, at early time points, occurs primarily on fiber surfaces. Deposition of fibrin, a fibrous protein involved in acute inflammatory responses, can facilitate cell attachment within this optimal region at early time points. The current work compared physiological (3 and 5 g center dot L-1) and supraphysiological fibrinogen concentrations (10 g center dot L-1), using static in vitro seeding of HObs, to determine the effect of fibrin deposition on cell responses during the first week of cell culture. Early cell attachment within the interfiber spaces was observed in all fibrin-containing samples, supported by fibrin nanofibers. Fibrin deposition influenced the seeding, metabolic activity, and early stage differentiation of HObs cultured in the fibrin-containing fiber networks in a concentration-dependant manner. While initial cell attachment for networks with fibrin deposited from low physiological concentrations was similar to control samples without fibrin deposition, significantly higher HObs attached onto high physiological and supraphysiological concentrations. Despite higher cell numbers with supraphysiological concentrations, cell metabolic activities were similar for all fibrinogen concentrations. Further, cells cultured on supraphysiological concentrations exhibited lower cell differentiation as measured by alkaline phosphatase activity at early time points. Overall, the current study suggests that physiological fibrinogen concentrations would be more suitable than supraphysiological concentrations for supporting early cell activity in porous implant coatings.
... As for the PMFSS, Ducheyne et al. [18] produced a less porous PMFSS using two types of AISI 316L stainless steel fibers with diameters of 50 lm and 100 lm, of which the tensile and compressive properties were studied. Clyne and Markaki [10,19] fabricated highly porous sheets by using liquid phase sintering of short stainless steel fibers with diameter of 100 lm, followed by an electroplating step to coat the surface with a 5 lm thick copper layer. ...
A novel porous metal fiber sintered sheet (PMFSS) with three-dimensional reticulated structure was fabricated by using solid-state sintering method of copper fibers. Uniaxial compressive test was carried out to investigate the effects of porosity and manufacturing parameters on the compressive properties of PMFSS. During the compressive process, it was found that the PMFSS initially exhibited short-term elastic deformation, and then quickly entered into the compact densification deformation stage. The stress-strain plots showed no obvious yield stage in the whole uniaxial compressive process. Under given stress, the PMFSS with higher porosity exhibited higher strain, hence implying lower effective stiffness. Additionally, our results showed that higher sintering temperature or longer sintering time would soften the PMFSS. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.
... A possible problem [18, 19] with such highly porous metallic materials is that they are often mechanically weak, particularly in tension. However, certain types of porous metal, produced by bonding together metallic fibres [20], do exhibit promising strength and toughness levels. ...
This work relates to porous material made by bonding together fibres of a magnetic material. When subjected to a magnetic field, the array deforms, with individual fibres becoming magnetised along their length and then tending to line up locally with the direction of the field. An investigation is presented into the concept that this deformation could induce beneficial strains in bone tissue network in the early stages of growth as it grows into the porous fibre array. An analytical model has been developed, based on the deflection of individual fibre segments (between joints) experiencing bending moments as a result of the induced magnetic dipole. The model has been validated via measurements made on simple fibre assemblies and random fibre arrays. Work has also been done on the deformation characteristics of random fibre arrays with a matrix filling the inter-fibre space. This has the effect of reducing the fibre deflections. The extent of this reduction, and an estimate of the maximum strains induced in the space-filling material, can be obtained using a simple force balance approach. Predictions indicate that in-growing bone tissue, with a stiffness of around 0.01-0.1 GPa, could be strained to beneficial levels (~1 millistrain), using magnetic field strengths in current diagnostic use (~1 Tesla), provided the fibre segment aspect ratio is at least about 10. Such material has a low Young's modulus, but the overall stiffness of a prosthesis could be matched to that of cortical bone by using an integrated design involving a porous magneto-active layer bonded to a dense non-magnetic core.
... A possible problem with such highly porous materials is that they are unacceptably weak, particularly under tensile loading (Gibson 2000; Markaki and Clyne 2001). However, certain types of porous metal, produced by bonding together metallic fibres(Ducheyne, Aernoudt et al. 1978), do exhibit promising strength and toughness levels. ...
1. Background Replacement of hip, knee and other joints, usually as a treatment for degenerative arthritis, is becoming increasingly common, with the worldwide market currently worth about $5 billion and an estimated annual growth rate of around 9%. These operations bring pain relief to millions, but the treatment is plagued by a substantial problem. The stem of the prosthesis, which is commonly pushed down into a recess in the host bone, often becomes loose after a time. The problem is getting worse as joint replacement rates rise and operations are carried out on younger and more active patients. Prosthetic implants are attached to bone either with cement or via bone in-growth into a rough or porous surface. Although bone cement provides immediate fixation, cemented implants frequently loosen in time due to the poor wear and fatigue properties of such cement. Furthermore, in-vivo polymerization is likely to take place, with deleterious effects on the surrounding tissue. Strong bone-implant bonding can be achieved in the absence of cement by bone tissue growth into an implant surface which is rough or porous, preferably with channels of around 100-300 µm in diameter (Bobyn, Pilliar et al. 1980). However, this does not occur very readily or quickly and might typically take at least a couple of weeks - a period during which there is a serious danger of complete debonding if exercise is undertaken prematurely. It is now well established (Frost 1987; Akhouayri, Lafage-Proust et al. 2000; Mosley 2000) that bone growth is stimulated by mechanical stress and becomes sluggish in its absence. Resultant phenomena include loss of bone density and strength in astronauts after extended periods in a hypo- gravity environment and localised bone resorption adjacent to prosthetic implants, as a consequence of stress shielding. This latter effect arises because prostheses are stiffer than surrounding bone, inhibiting it from being strained. (Most metals have a stiffness of about 100-200 GPa, whereas that of cortical bone is about 7-27 GPa).
... However, cellular materials composed of bonded networks of metallic fibres, consolidated by sintering at contact points, are also of interest, particularly since they can be manufactured in a flexible and economic fashion. Mechanical properties of such networks have previously been investigated by several researchers [10][11][12][13]. The mechanical properties do of course depend quite strongly on the network architecture [14]. ...
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.
... Some research has been performed on the determination of mechanical properties of different fibre structures. Ducheyne et al. [11] manufactured a fibre structure with a relative density of 0.4 using stainless steel fibres and investigated tensile and compressive properties. Liu et al. [12] manufactured a steel wire mesh with different relative densities 0.437-0.661 ...
The present study investigates mechanical properties of a novel sintered metallic fibre structure with different relative densities (i.e. 0.19, 0.27, and 0.46). The compressive mechanical properties Young's modulus, Poisson's ratio and 0.2% offset yield stress are determined. For this purpose, state of the art simulations are performed based on the real material structure using micro-computed tomography images. Computed results are compared with experimental uni-axial compression tests and good agreement between both methods is observed. Numerical analysis allows the investigation of directional dependence and mechanical anisotropy is observed to be governed by the fibre orientation. In addition, Young's modulus and 0.2% offset yield stress increase with rising relative density.
... 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.
... Kostornov et al. [10] produced a porous sintered metal using Ni-Cr alloy fibers as a starting material, investigating the relationship between low porosity and tensile strength. Ducheyne et al. [11] produced a new type of low-porosity PMFSS using AISI 316 L stainless steel fibers with the two kinds of diameters of 50 m or 100 m, studying the tensile and compressive properties of the sheet. Clyne and Markaki [12,13] produced highly porous sheets by first using liquid phase sintering of short stainless steel fibers with a diameter of 100 m, followed by an electroplating step to coat the surface with a 5 m thick layer of copper. ...
A novel porous metal fiber sintered sheet (PMFSS) with a three-dimensional network structure has been produced via solid-state sintering of copper fibers. The copper fibers, approximately 100 μm in diameter, were fabricated using the cutting method. In this study, a uniaxial tensile test was used to study the tensile fracture process of the PMFSS. The effect of the porosity and sintering parameters on the tensile properties of the PMFSS was investigated in detail. It was found that the tensile strength of the PMFSS decreased significantly with an increase in the porosity, but the elongation remained relatively constant with different porosities. In addition, for sintering temperature between 700 °C and 900 °C, the tensile strength increased with increasing sintering temperature and decreased with increasing sintering time.
... The fracture behaviour (tensile strength and fracture energy) of metallic fibre network materials has been relatively little studied. Ducheyne et al. [15] measured the tensile strength of sintered 304 stainless steel mats (diameter 50-100 lm), and found it to range up to tens of MPa, as the density was increased up to ∼ 40 %. Typically, most steel-based fibre network materials (with relative densities of about 5-20 %) exhibit strengths of a few MPa. ...
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 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.
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.
A novel methodology to design porous fibre network structure or material has been proposed. The methodology is computational in nature considering a MATLAB based algorithm, which was uniquely devised to achieve stochastic fibre networks with layered structure. The fibre network architecture, which is actively controlled by the algorithm include network porosity, fibre orientation and fibre-segment aspect ratio. The algorithm generates coordinates of individual fibres which are then modelled into a planar mesh. Further, the fibre network structure is achieved by stacking layers of several such meshes considering an inter-mesh overlap volume. The designed porous structure has achieved close to 90% porosity. Its fibre orientation distribution was isotropic with fibres laying uniformly in all directions in the mesh planes. Overall, the developed porous fibre network structure has been computationally validated to possess the desired structural parameters.
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.
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.
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.
In der Absicht, die Langzeitzuverlässigkeit bleibender Implantate zu verbessern, wurden einige neue Techniken der Knochenfixation der einzelnen Komponenten untersucht. Durch Arbeiten verschiedener Laboratorien ergab sich unabhängig voneinander, daß durch mechanische Verkeilung poröser Implantatdeckschichten Knochengewebe in die entsprechenden Poren einwächst und dies nun eine der meist versprechendsten Methoden darstellt [4, 8, 10, 11, 13].
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.
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.
The use of polymethylmethacrylate bone cement has unquestionably revolutionized the field of total joint replacement. Recently, however, long-term clinical results in which total joint replacement has been evaluated for periods in excess of 5–10 years have revealed that this system of prosthetic fixation is far from ideal. A significant degree of prosthetic loosening has been observed, demonstrating the need of a more perfect method of skeletal attachment of prosthetic devices. Thus, much research is currently being conducted on methods of biologic fixation of prosthetic devices, thereby avoiding the necessity for use of the acrylic bone cement.
Novel stainless steel porous twisted short fiber materials (PTSFMs) with spatial composite intertexture structure are produced by compaction following with sintering of twisted short fibers. The stainless steel twisted short fibers are fabricated using a cutting stainless steel fiber ropes method with a self-developed rotary multi-cutter tool. The porous structure of the stainless steel PTSFMs exhibits a large difference in the through-thickness and in-plane direction, which results in differences in compressive behavior. During the compressive process, it is determined that the stainless steel PTSFMs exhibit typical elastic-plastic behaviors (three deformation stages) in the in-plane direction, but in the through-thickness direction, entered the compact densification zone after short-term nonlinear elastic deformation without a plastic platform stage. The compression deformation resistance in the through-thickness direction is obviously stronger than that in the in-plane direction at a given porosity. The compression strength and the anisotropy both decreased with increased porosity. The compression properties are anisotropic, which also result in different energy absorption efficiencies of the two directions. The relationship between the porosity and the energy absorption efficiency is not monotonically increasing or decreasing, but with the change of porosities, there is an optimal porosity, which has relatively high-energy absorption efficiency.
The main long-term problem with total hip arthroplasty remains aseptic loosening, particularly of the cup. This was pointed out by Charnley in 1979 [31] and is demonstrated by the survivorship analyses of Sutherland et al. [240], Morscher and Schmassmann [170], and others (Fig. 1). Mulroy and Harris [177] found a 20-fold increase in the rate of acetabular loosening between 5 and 11 years.
Das Hauptproblem der Hüftgelenkarthroplastik bleibt die aseptische Lockerung, speziell diejenige der Hüftgelenkpfanne. Dies hat Charnley [31] bereits 1979 betont und konnte später durch die Überlebenskurven von Sutherland et al. [240], Morscher u. Schmassmann [170] aufgezeigt werden (Abb. la, b). Mulroy u. Harris [177] fanden eine 20fache Zunahme der Pfannenlockerung zwischen 5 und 11 Jahren. Während die Lockerungsrate des Femurschaftes einen ungefähr linearen zeitlichen Verlauf zeigt, ist eine Pfannenlockerung in den ersten 6–8 Jahren postoperativ relativ selten, nimmt dann aber nach dem 10. postoperativen Jahr exponentiell zu [170].
The objective of knee joint arthroplasty is to eliminate pain and to maintain or restore knee stability and the best possible joint mobility. Until recently, it has often proved difficult to attain these goals, above all to retain them over a long period of time. Experiences reported the last 10 years describing a large number of knee joint arthroplasties [2, 3, 6–8, 10–12, 14, 21, 22, 26, 29, 41, 42, 50, 51, 56, 57, 59, 60, 61, 63, 68, 72] indicate that the complicated structure of the knee joint requires the application of appropriately complex surgical techniques with a high possibility of failure [15, 20, 32, 67, 73, 74, 77, 79, 82, 84]. In particular, as in the hip joint, it has been shown that loosening of the implant constitutes a major problem in knee joint arthroplasty. Loosening of the implant is a very frequent feature occurring in long-term follow-ups, especially for hinge prostheses with long anchoring stems [4, 13, 25, 28, 30, 31, 48, 49, 64, 69, 75]. Knee joint arthroplasty has clearly advanced sufficiently to allow more physiologically related movement through the preservation of the natural stabilising elements, i. e. muscles, tendons and ligaments, especially the collateral ligaments and, independent of the corresponding prosthesis model, the cruciate ligaments, in particular the posterior cruciate ligament (PCL). It has also been possible to preserve or largely restore normal kinematics in the knee joint [27, 38, 44, 46, 66, 76, 81], which also provide good preconditions for long-term success of the knee reconstruction [39, 40, 78]. However, to preserve or restore normal kinematics the tensioning of the ligaments should be coordinated, and as little bone as possible should be resected; thus, knee joint arthroplasty has become ever more elaborate in terms of surgical techniques and requires increasingly sophisticated instruments [24, 43].
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.
In an effort to improve the long-term reliability of permanent implants, several new techniques have been investigated for the skeletal fixation of the components. Independent work at various laboratories has shown mechanical interlocking by bone ingrowth into porous coatings to be one of the most promising techniques in this regard [4, 8, 10, 11, 13].
Nowadays when we speak of cementless fixation of hip endoprostheses, we are actually returning to the early days of hip arthroplasty. This is not to say, however, that the use of bone cement is a thing of the past.
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.
This chapter describes the processing and properties of metals containing significant fractions of porosity, processed using powders. The basic concepts used in porous materials research are introduced and the different types of processing techniques that have been explored are surveyed. The reported property data for different foams are collated and used to illustrate the range of properties that have been achieved and methods to predict the properties of porous metals from elementary knowledge about their structure are discussed. Finally, the outlook for porous metals research and some likely future directions of fruitful enquiry are suggested.
Creating 'smart' biomedical devices with the potential for controlled actuation in vivo has been a long-standing scientific pursuit in therapeutic medicine. The present work focuses on a bone regeneration scaffold based on ferromagnetic fibres designed to induce in vivo modelling of in-growing periprosthetic bone by the application of an external magnetic field of clinical magnitude. We present the conceptual basis of such a 'magneto-active scaffold', the properties of prime interest and how these properties can be controlled.
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.
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.
A method is developed which predicts the elastic moduli of homogeneous isotropic two-phase materials of arbitrary phase geometry. The geometry is considered analytically using three parameters, the magnitudes of which characterize any type of composite (particulate materials, phase-symmetric powder materials etc.). The characteristic parameters may be estimated from a table given in the paper. The prediction method is tested successfully against a number of experimental results and results from finite element analysis. An algorithm is outlined by which the numerical procedures are easily carried out with a small calculator. Some analogies are given which generalize the applicability of the method to include predictions of viscoelastic, electric, magnetic, thermal and diffusion properties. Finally it is shown how the theory may also be used when transversely isotropic composites are considered.
Abstract Das wachsende Interesse an der Schaftgestaltung von Hüftendoprothesen läßt immer neue Formvarianten entstehen, ohne daß mit
Sicherheit feststeht, welchen Kräften der proximale Femurschaft ausgesetzt wird. Um diese Kräfte zu verifizieren, wurden computergesteuerte
Spannungsanalysen verschiedener Prothesentypen in einem Kunststoffnormfemur vorgenommen. Die Messungen von Druck-und Zugspannungen
und erstmalig auch Torsionskräften zeigten eine zum Teil erheblich veränderte Kraftentfaltung, die als Hauptursache für das
Auslockern von Hüftendoprothesen diskutiert werden muß.
Abstract Growing interest in hip endoprothesis is inducing a lot of ideas for formgiving, without having cleared the adequate strength
to the proximale femur. To know more about these forces, we made computerized tension-analyses of some different types of
prosthesis in a normed artificial femur. Measurement of press-and tensile tensions on one hand and the torsion-tensions on
the other hand showed some enhanced forces which might be the reason for slackening of hip endoprosthesis.
This report is a survey of the mechanics of beam and plate structures laminated of fiber-reinforced composite materials having different elastic and thermoelastic properties in tension and compression. Examples of such materials include tire cord-rubber, wire-reinforced solid propellants, and soft biological materials. Specific topics covered include: mathematical models of fiber-reinforced bimodular materials and their experimental verification; static and dynamic analysis of laminated and sandwich beams; plane elasticity; analysis of deflection and free and transient vibration of laminated plates and shells. In all of these analyses, thickness-shear deformation and rotatory inertia are included. The solution methods used include closed-form, transfer-matrix, and finite-element techniques. (Author)
We developed a titanium fiber mesh block (TFMB) to use as an alternative to autogenous bone, grafts for vertebral interbody
fusion. In in vitro tests, we measured the surface pore size and conducted weight loading tests of TFMB with porosities of
50% and 60%. For invivo testing, we grafted TFMB in 11 mongrel dogs for intervertebral fusion and evaluated bone ingrowth
into the grafts and the bonding of TFMB with bone. The mean surface pore size was 375±289 μm for 50% porosity TFMB and 445±440
μm for 60% porosity TFMB. In the in vitro weight loading test, 60% porosity TFMB showed 50%–60% of the elastic modulus of
50% porosity TFMB, and both materials showed a similar yielding load. After the grafting of 60% porosity TFMB, bone in-growth
occurred to a depth of 2.3 mm at 3 months and to a depth of 3.6 mm at 6 months; while the values were 0.7 mm and 1.5 mm, respectively,
in 50% porosity TFMB. In a push-out test conducted 6 months after grafting, 50% and 60% porosity TFMB showed similar bone
bonding strengths. These results suggest that 60% porosity TFMB implant will be suitable to using for spinal interbody fusion.
Kinked, short-length, fine wire can be molded by conventional powder metallurgy procedures and sintered to a porous composite with large proportions of interconnecting voids. The material has potential applications for implanted prosthetic systems. The material behaves in a nonlinear elastic fashion which may be approximated as two linear elastic processes. In the strain range of 0 to about 0. 5 percent, the elastic modulus can be less than 1 kg/mm**2. Total elastic strain range is from 1. 5 to 4%.
1.
The relationship between the modulus of elasticity E and relative density ϑ of fibrous metals is described by Eq. (2), in which the minimum value of the power m is close to 2.
2.
The contact ultimate strength obc=ob/α=obEc/E for fibrous copper and stainless steel, determined from Eq. (1), was independent of porosity within the limits of experimental error and had a value corresponding to the σb of the nonporous metal in the annealed state. This indicates that the modulus of elasticity E is a basic characteristic for evaluating the contact cross-section and strength of porous fibrous metals.
3.
We obtained data on the damping decrement as a function of the density of porous fibrous metals.
There is a need in anatomical restoration for a reliable, long-term method for attaching artificial materials to living tissue. The advantages and disadvantages of porous metals for attachment are discussed, and several porous metal types are compared. A unique porous metal called Void Metal Composite (VMC) is described. Preliminary data are reported on ingrowth and interface shear strength of VMC implanted 12 months in cat femora. Additionally, data are reported for interface strength in shear and cyclic loading for 6 week implants in goat femora.
To serve as a component of a load-bearing skeletal prosthesis, a porous material should offer the following attributes: (1) pore channels over 100μ in diameter; (2) continuity of pore channels; (3) matrix material inert and compatible with animal tissues; (4) manufacturable as thick coatings or thin-walled complex surface assemblies; (5) manufacturable to precision dimensions; (6) large compliance comparable to bone; (7) crack resistance, particularly under impact.
A porous composite was manufactured by molding and sintering short metal fibers, which fulfilled all of these requirements. The composite was manufactured both with titanium and Vitallium fibers.
Experimental implants were performed in dogs and rabbits indicating peripheral bone formation around the implant at 2 weeks and penetration from 3 weeks on. Shear strength values at the prosthesis-bone interface were in the range of 20 kg/cm2 3 weeks after implantation.
Femoral prostheses implanted in dogs revealed fixation by bone formation and maintenance by bone ingrowth up to 1 yr following implantation.
Massive incorporation with bone of skeletal segmental replacements for the baboon's femur were seen up to 3 months following implantation.
Practical problems that can be encountered with the use of porous fiber metal composites for prosthesis fixation relate to: (1) the possibility of long-term corrosion occurring in an implant with a very large surface area; (2) technical problems with implantation requiring intimate contact between the fiber metal surface and the bone and (3) the difficulties in removing an implant which has failed for mechanical reasons requiring that a device manufactured using fiber metal composites for fixation be absolutely failure free from a mechanical viewpoint.
Variational principles in the linear theory of elasticity, involving the elastic polarization tensor, have been applied to the derivation of upper and lower bounds for the effective elastic moduli of quasi-isotropic and quasi-homogeneous multiphase materials of arbitrary phase geometry. When the ratios between the different phase moduli are not too large the bounds derived are close enough to provide a good estimate for the effective moduli. Comparison of theoretical and experimental results for a two-phase alloy showed good agreement.
The title problem concerns two isotropic phases firmly bonded together to form a mixture with any concentrations. An elementary account of several theoretical methods of attack is given, among them the derivation of inequalities between various moduli. The approach is completely general and exact. Additionally, the problem is fully solved when the phases have equal rigidities but different compressibilities, the geometry being entirely arbitrary.
The present status of skeletal fixation of permanent orthopedic implants by poly(methyl methacrylate) (PMMA) is discussed. It is proposed that alternatives to the acrylic cement can improve the skeletal fixation. The present paper is concerned with the fixation method by bone ingrowth into pores of the implant surface.
Two different implantation models have been designed to investigate the influence of load bearing upon ingrowth in surface pores of the implant: intramedullary nails as a means of fixation of a femoral pseudarthrosis and hinged knee prostheses. In each animal, implants with identical material characteristics (pore size, density, and thickness of the porous layer) but different loading conditions were used: one implant was “statically” loaded, the other “dynamically.” This procedure allows the evaluation of ingrowth with regard to load bearing only.
Two different mean pore sizes, viz., 87 and 110 μm, have been used with the two models. After an 8 week implantation period, bone ingrowth was evident for the statically loaded implants. Calcified tissue ingrowth was, however, not observed in the dynamically loaded implants. The discrepancy in bone ingrowth behavior between the statically and the dynamically loaded implants has been attributed to 1) the gross movement or the micromovement existing at the bone prosthesis interface and 2) the fact that the critical mean pore size for ingrowth with static loading is smaller than the one with dynamic loading.
The experimental implantations allow still another conclusion: the results suggest that designs of present clinical prostheses fixed by bone cement cannot be used with the alternative fixation by bone ingrowth unless the deisgn has been changed in a fundamental way. Mechanical factors as well as the phenomenology of bone ingrowth fixation account for this conclusion.
The compressive properties of human cancellous bone of the distal intracondylar femur in its wet condition were determined. Specimens were obtained from six cadaveric femora and were tested at a strain rate of 0.002, 0.10 and 9.16 sec−1. It was found that the compressive strength decreases with an increasing vertical distance from the joint. The highest compressive strength level was recorded in the posterior medial condyle. Correlations among the mechanical properties, the bulk specimen density and the bone mineral content yield (i) highly significant correlations between the compressive strength and the elastic modulus (ii) highly significant correlations between the compressive strength or the modulus of elasticity and the bulk specimen density (iii) a doubtful correlation between the compressive strength and the bone mineral content. All recorded graphs of the impact loaded specimens displayed several well defined stress peaks, unlike the graphs recorded at low loading rates. It can be concluded that upon impact loading the localized trabecular failure which is associated with each peak, does not affect the spongy bone's stress capacity in a detrimental way.
A survey is given of the mechanical failures of the femoral component of Charnley and Charnley‐Müller type total hip prostheses. Fractographic analysis reveals that all the prostheses have broken by metal fatigue.
A review of the clinical data has been combined with a metallurgical and a mechanical study in order to assess the reasons of the mechanical failures.
The following conclusions have been reached. The prosthesis should be inserted in varus position with regard to the axis of the intramedullary canal, and the prosthesis should be made of an alloy with appreciably higher yield stress and fatigue strength than the alloys of the investigated broken Charnley and Charnley‐Müller type prostheses.
The factors responsible for clinical stem failures of total hip joint prostheses were studied by instrumenting the Charnley, Mueller and Trapezoidal-28 prostheses with strain gauges and subjecting them to various conditions of load and acrylic fixation. Loading tests of stems which were supported as simple cantilever beams demonstrated that the Mueller prosthesis was comparatively weak in regions of observed clinical stem fractures. Simulated femoral loading tests of prostheses securely fixed in acrylic bone cement showed low stress levels in the stems and necks. Varus placement of the stems caused a marked increased stress in the stem; this condition should be avoided at surgery. Our tests showed that a prosthesis which is loose in the acrylic also raises stress levels in the distal stem. As acrylic is setting, movement of the prosthesis must be avoided. Lack of adequate proximal medial support for the stem, due to poor quality bone stock or acrylic fracture, will create dangerously high stress levels in the stem: this emphasizes the importance of good cement filling technique and proper patient selection.Three clinical stem failures have been analyzed using the results of these tests. We have concluded that inadequate stem design and varus placement were contributing factors in the fatigue fracture of a cast cobalt-chromium-molybdenum Mueller stem. Contributing factors of the failure of two cast 316 LVM stainless steel Bechtol stems were low strength metal and technical error in cementing one of them which was apparently loose in the acrylic at the time of surgery.
Specimens of cancellous bone were obtained from normal autopsy and arthritic knees at operation. The bone was removed from the locations of the contact areas at 0°, 45° and 90° flexion. Compressive strength was measured and compared with the bulk specimen density, the linear absorption coefficient, μB, and the bone material density. In addition, the trabecular patterns themselves were studied.Strength varied with position in the joint so as to indicate load-bearing function. Bone material density did not relate to strength. Bulk specimen density and μB were found to correlate with strength, yet did not fully account for the wide strength variations. Trabecular organization however was shown to be a significant factor. It was concluded, therefore, that specimen strength was a function of several factors.
The feasibility of the use of porous ceramic materials in the permanent repair of skeletal defects was studied from the standpoint of physiological compatibility and in growth of natural bone. High-fired calcium aluminate samples in the form of quarter-inch diameter cylindrical pellets containing interconnecting porous networks were implanted in vivo into canine femurs for 4-, 11-, and 22-week periods. The implants had 65% porosity with pore size falling within one of five distinct ranges from less than 45 μ to about 200 μ in diameter.
Thin sections were prepared by grinding (poly) methyl methacrylate-mounted cross sections of the femurs containing the implanted ceramic samples and adjacent soft tissues. Tissue-prosthetic compatibility was determined using standard histological thin section procedures, electron microbeam probe examinations, autoradiographic techniques, microfadiographic techniques, microchemistry techniques, and ultra-violet fluorescent techniques. Optical microscopic evaluations of each section showed the ceramic samples to be bound lightly by natural bone and gave no detectable signs of tissue incompatibility. Minimum pore size for significant ingrowth of natural bone was indicated to be between 75 and 100 μ.
Recent results indicate varying degrees of bone ingrowth into porous metal and ceramic bodies. Such homogeneously porous ceramic and metal implants generally possess inadequate mechanical properties, limiting their application to low stress or nonstructural applications. An experiment was performed wherein titanium porous coatings were applied to a wrought titanium bone implant. These surfaces were achieved by plasma spraying of titanium hydride powder, depositing a mixture of wellbonded titanium-titanium oxide with pore diameters varying from .002 to .005 in.
Implant specimens were placed in sheep femora for periods of 14 and 26 weeks. No adverse affects were noted. Interface shear strengths were determined by torque tests which indicated approximately a twenty-fold increase over similar tests performed on uncoated control specimens.
A fiber titanium composite has been developed and its potential application as a method of skeletal fixation for internal prosthetic devices has been studied.
Titanium fibers, 0.19 millimeter in diameter, were cut in short lengths, compressed in dies to predetermined densities, and sintered under vacuum.
The composite exhibited adequate strength and its compliance was larger than bone.
Samples were implanted in the trochanteric and in the supracondylar areas of the femora of rabbits and dogs. Peripheral bone formation was evident at ten days, bone ingrowth was demonstrated at two weeks, and penetration deep into the samples was seen three weeks following implantation.
The shear strength of the bond at the implant bone interface in the trochanteric region of dogs was measured hs tensile tests. The strength increased significantly until the second week and remained constant thereafter until twelve weeks following implantation. Average values were in the range of 20 kg/cm2.
These findings are discussed in terms of the configuration of a prosthetic device. A fiber metal composite in the form of a thin sleeve surrounding ansd bonded to a central solid metal core would provide fixation to bone and uniform stress distribution at the implant bone interface.