Generally, for the fracture problem in an actual construction, three-dimensional cracks exist in most cases, and in crack propagation, the stress intensity factors K_I, K_II and K_III usually act in single or mixed modes. The separation of K_I and K_II has already been achieved, but K_III has been studied little. In the paper, the mixed mode stress intensity factors K_II and K_III are determined experimentally by combining the caustic method and photoelastic stress freezing method.

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The effect of the stress ratio on growth behavior of mode II interlaminar fatigue cracks was studied with unidirectional carbon/epoxy laminates, Toray T800H/#3631. The end loaded split (ELS) specimens were used for tests under negative stress ratios. For each stress ratio, the crack propagation rate was given by a power function of the stress intensity range, ΔK_II, or the maximum stress intensity factor, K_IImax, in the region of rates above 10^-9 m/cycle. Below this power law region, there exists a threshold value of the stress intensity range, ΔK_IIth, for the fatigue crack propagation. The value of ΔK_IIth was constant for the stress ratio between -1.0 and 0.6. In the power law region, both ΔK_II and K_IImax affect tht crack propagation rate. The effect of K_IImax decreases as the crack propagation rate decreases. In the near-threshold region, the crack propagation rate is controlled only by the ΔK_II value ; the value of K_IImax has no effect on the crack propagation. A simple equation was proposed for predicting the propagation rate of mode II fatigue cracks under various stress ratios. Predictions agreed well with the experimental results for both positive and negative values of the stress ratio. The effect of the stress ratio on propagation mechanisms of fatigue cracks was discussed on the basis of fractographic observation.

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The out-of-plane bending fatigue tests were performed for plate specimens with several different thicknesses. Then the effect of the plate thickness on aspect ratio of the surface crack and fatigue life for crack extension were analyzed through elastic fracture mechanics. The decrease in the aspect ratio with progress in crack extension process was successfully estimated by the proposed numerical calculation. Furthermore, the life calculations showed that the life required for the crack to extend up to a given crack length increased with decrease in plate thickness at a given stress, and such a thickness dependency of fatigue life appeared much more significantly in the extension process of the larger crack than in that of the smaller crack.

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This paper presents the results of a study on the effects of the shot-peening process on the fatigue characteristics of austempered ductile iron (ADI). Experiments mainly involve surface durability tests using cylindrical roller specimens and bending fatigue tests, as well as X-ray stress measurements. The elasto-hydrodynamic lubrication (EHL) theory was used in the determination of surface durability. It was found that the surface durability of the shot-peened ADI was slightly lower than the of the non-shot-peened ADI, and this difference was attributed to the difference in surface roughness. Moreover, it was found that residual stress does not affect the surface durability of the shot-peened ADI. Results also showed that the shot-peening of the ADI is useful for improving the bending fatigue strength. Consequently, from the viewpoint of fatigue strength of ADI, surface roughness, especially as related to the surface durability, should be strongly considered in the case of application of shot-peened ADI to machine elements subjected to bending and/or sliding abrasion.

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An influence of cooling rate on the fatigue reliability of aluminum alloy castings (AC4CH) was investigated. The results obtained were as follows : (1) As the cooling rate of AC4CH was increased, the porosities and the microstructure were controlled fine. (2) The fatigue strength of AC4CH produced through rapid cooling rate was superior to that produced through slow cooling rate, specially on the fatigue limit (N=10⁷). (3) The effect of stress gradient on the fatigue limit is due to the probability that the maximum stress can put on the largest porosity in the specimen. (4) Micro porous defects were always observed at the origin of fatigue crack. Then, it could be interpreted that the fatigue life was related to the size of porous defect, based on fracture mechanics. (5) From the above relation and the statistical analysis on the size of porous defect, the fatigue limit of 99% remaining probability could be estimated.

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The method to improve the fatigue reliability of recycled-advanced reinforced PA·MXD6 was examined. Especially, the effects of the mezoscopic factor on the fatigue crack propagation were paid attention to. Main results were obtained as follows ; (1) As the recycled material was blended with the virgin material in recycling process, fatigue reliability of 'Ecomaterial' was remarkably improved. Practically the threshold value ΔK_th of` 'Ecomaterial' was improved by blending virgin pellet, as the rate of equal to blending value. Then the influence of virgin pellet blended in recycling process on fatigue reriability could be estimate by the law of mixture. (2) From fractgraphy with using SEM and analysis on the length of glass fiber, it could be interpreted the long glass fibers of virgin pellet contributed to the bridging effect on fatigue crack opening in 'Ecomaterial'. (3) The crack opening displacement in 'Ecomaterial' was estimated though measurering the crack tip heating. Then, it was intermedium between 'fully recycled material' and 'Virgin material'

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In order to estimate fatigue reliability of austempered ductile iron (ADI) with austempered ferrite-retained austenite dual structures, the influence of casting defects on the fatigue strength was examined through fractography. Fatigue testing as conducted under tension-tension loading, R=0. 05. It was found through fractography that the fatigue crack initiated at the micro porosity. This, the fatigue life, N, was mutually related to a presented parameter K_a=2S √(πa), where S is the stress amplitude and as the dimension of micro defect initiating a fatigue crack. By comparing ADI with spheroidal graphite iron of full pearlite matrix structure in using K_a-N diagrams, it could be understood that austempered Ferrite-retained Austenite dual structures had higher resistance against the meso scopic crack initiating at the micro porosity than the full pearlite matrix structure.

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It is shown from the calculation of SiO₂ static fatigue strength that the strength degradation behavior under the influence of atmosphere can be analyzed using the interatomic potential which is based on the Tersoff potential and extended to take the charge transfer effects into account. The force-elongation curves of Si-O interatomic bonds of SiO₂ with and without H₂O in the atmosphere are calculated. Based on these curves, crack propagation behavior is analyzed. The calculated results correspond to the experimental results well. Moreover, the calculated values of the decrease of the strength caused by H₂O show fair agreement with the experimental values.

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An automatic fatigue crack tracking system with an image processor has been newly developed. This system consists of a microscope with a CCD camera, an image processor, a position measuring system, an automatic stage which moves the microscope, a personal computer and a fatigue testing machine. The tracking procedures fall into the following four distinct steps. Step 1 : When a maximum load is applied to the cracked specimen, the system obtains the image around the crack tip and stores the image to the frame memory. Step 2 : After appropriate stress cycles, the system obtains the image at the same position again. Step 3 : The image processor freezes the motion and subtracts the stored image from the image obtained in Step 2. Then the subtracted image is emphasized by adding the offset brightness level. Step 4 : The dark image which is obtained by preceding procedures, is tracked with a template by the position measuring system. The amount of shift of the template represents the length of fatigue crack extension. The system moves the microscope by a distance equal to the length of the crack extension. We applied this system to the fatigue crack propagation tests on steel and Si₃N₄ ceramics, and confirmed the reliability of our data.

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The degree of diminution of fracture ductility varies with prestrain level. This behavior is investigated in the present study by using carbon steel and 70/30 brass. Transition of the fracture ductility appears at about a pretorsional strain of unity in the case of carbon steel. On the other hand, in the case of 70/30 brass, fracture ductility decreases smoothly and this transition behavior is not observed. However, the main cause of the loss of fracture ductility of the two materials is that the surface layer of the material becomes brittle due to the shear strain, and tensile fracture starts from surface cracks initiated by tensile deformation. The difference in diminution behavior of ductility between the two materials is thought to be due to differences in crystal structure and thus in the brittleness of the surface layer. The ductility of this surface layer is greatly reduced after the transition in the case of carbon steel.

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Microstructure and mechanical properties of HP, HP/GP and HP/HIP-Si₃N₄ were studied using scanning electron microscopy, bending tests and the indentation fracture method. The distribution of grain diameter was analyzed to clarify the relationship between microstructure and mechanical properties (bending strength and fracture toughness value). It is shown that bending strength increased with decreasing the grain diameter. The results also showed that a Hall-Petch relationship was recognized for grain diameter and fracture stress. The fracture toughness value shows a linear relationship with σ_F√(βd_a), and is closely related to aspect ratio of Si₃N₄ grain. From these grain morphological analysis results, it is concluded that the microstructure composed of Si₃N₄ grains having both small grain diameter and large aspect ratio is effective to improve both fracture strength and fracture toughness.

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A four point bending test was carried out on sintered α-type SiC speciments to examine the scattering of strength. On the other hand, nondestructive material characterization by means of impedance measurement of the specimen for a wide range of frequency of 5 Hz∼100 kHz was performed. As a result, it was found that the complex plane plot of the impedance is composed of two semicircles. The diameter of the smaller semicircle (high-frequency side) was almost the same for all specimens, but that of the larger semicircle (low-frequency side) was different between bulk end specimens and bulk center specimens. This impedance variation from specimen to specimen agrees well with those of the bending strength. From the composition analysis of each specimen, it was found that the bending strength and the diameter of the low-frequency semicircle is affected by the content of free carbon assumed to exist at the grain boundaries. Possible evaluation of the material properties of SiC by impedance spectroscopy seems to be promising.

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Epoxy adhesives were modified with CNBR (cross-linked acrylonitrile butadiene rubber) to increase their fracture toughness. Strengths of double cantilever beam specimens fabricated with unmodified and modified epoxy adhesives under Mode I loading were measured. The crack extension resistance given by strain energy release rate G was obtained from the test. Rubber-modified adhesives show higher fracture toughness (the maximum crack extension resistance) than unmodified adhesive. The crack initiates at a relatively low G and grows as G increases. For unmodified adhesive, the maximum crack extension resistance is almost the same as the crack extension resistance in steady-state crack growth. On the other hand, the maximum resistance appears before the crack grows steadily. The variation of crack extension resistance with respect to crack length was influenced by rubber content. Adhesive thickness also affects the crack extension resistance of rubber-modified epoxy adhesives. The fracture surface topology varies according to rubber content.

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In our previous papers, it was found that ring crack initiation strength of gas pressure sintered silicon nitride evaluated by the sphere indentation method could not be related to conventional bending fracture strength of the same material, using the concept of effective area based on the Weibull distribution. In the present paper, to find the cause of this, a ring crack initiation model of a surface microcrack was applied. Using this model, the ring crack initiation strength was interpreted from the viewpoint of fracture mechanics. The dependence of ring crack initiation load on sphere radius was also interpreted using this model.

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Influence of matrix resin on tensile strength properties and splitting fracture toughness in unidirectional carbon fiber-reinforced plastic (CFRP) laminates has been investigated. Tensile tests and splitting fracture toughness tests were carried out on two kinds of CFRPs (carbon/thermoplastic systems ; 3KCF/Nylon 6 and 3KCF/modified Nylon). The modified Nylon was developed to improve the adhesion on the basis of Nylon 6. The performance of the present CFRPs was discussed in comparison with that of carbon/epoxy system (AS4/3501-6). It is noted that the present CFRPs exhibit the high strength and high ductility in 90°and 45°directions to the fibers. This result predicts that the present CFRPs have the potential for high resistance to the splitting in unidirectional laminate and to the transverse cracking in multidirectional laminate. On all the unidirectional CFRPs, the splitting fracture toughness under pure mode II is higher than that under pure mode I and the splitting is controlled by the tensile stress intensity in the wide range from pure mode I to mixed-mode loading. The fracture toughness for splitting in CFRP is drastically increased by changing matrix resin from epoxy to Nylon 6, and furthermore is improved by modified Nylon.

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This paper describes numerical solutions of singular integral equations of the body force method in interaction problems of ellipsoidal inclusions under uniform tension. The problems are formulated as a system of singular integral equations with Cauchy-type or logarithmic-type singularities, where the densities of body forces distributed in the r-and z-directions of infinite bodies having the same elastic constants of the matrix and inclusions are unknown functions. In order to satisfy the boundary conditions along the inclusions, eight fundamental density functions proposed in our previous paper are used. Then the body force densities are approximated by a linear combination of the fundamental density functions and polynomials. The present method is found to give rapidly converging numerical results for stress distribution along the boundaries of both the matrix and inclusions.

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In this paper we present a method of simulation for temperature control in transient heat conduction fields. The inverse analysis method using the boundary element method and the Kalman filter algorithm is applied to the computer simulation. The temperature control problem is such that the conditions on part of the boundary should be determined to achieve the requirement of responses on the other part of the boundary. The boundary element method is used to estimate the error between the target value and the temperature response, while the Kalman filter algorithm is applied to determine the unknown control parameters by minimizing the error. Numerical simulation is carried out for a few examples to demonstrate the usefulness of the proposed method.

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A creep constitutive equation is important for estimating creep deformation for structural designs under high temperatures. We can formulate the creep constitutive equation by characterizing a large number of creep curves. The characterization of a creep curve involves dividing the creep curve into three regions : transient, steady state and accelerating creep regions. Such characterization cannot be performed manually because of the massive amount of numerical data. This paper proposes a new algorithm for the characterization of the creep curve using fuzzy set theory. We use the fuzzy set theory for determining threshold levels between each region, because those levels have high fuzziness. The new algorithm enables us to mechanically characterize the creep curve without manual computation as well as to deal with massive amount of numerical data in a short time.

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Transient heat conduction and thermal stress analysis of hybrid laminated composite materials are very important for composite structure design because they are heated during the manufacturing process. Anisotropy of thermal conductivity must be considerd in heat conduction analysis of such composite materials as FRP. Assuming that heat conducts uniformly in the normal direction in thin structures they can be modeled by thin shell elements. In thermal stress analysis of unsymmetrically laminated shells, the coupling effect between plane stress and bending stress must be considered. In this paper, an FEM transient heat conduction and thermal stress analysis system taking glass translation into consideration for hybrid unsymmetrically laminated shell structures are described. As a numerical example, the thermal stress of CFRP laminated plates are investigated. As a result, it is recognized that thermal stress of laminated composite materials is sensitive to glass translation.

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In this paper, some regularized boundary integral formulations of the double-layer potential method are presented for two-dimensional classical potential problems. Some known paticular solutions are superposed on the conventional integral representations so that the cauchy principal value integrals for the potential and the hyper-singular integrals for its derivatives in the original intergral representations are regularized. Moreover, in order to extend this approach to external problems, the boundary integral equations formulated for the unit source distribution along the boundary are also presented. The singular elements are employed to approximate accurately the singular behavious of the potential near the corners. Sone numerical calculations are carried out for typical models and is shown that the results, especially the singular distributions of the potential gradients around the corners, are obtained with high accuracy.

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The optimization problem of a hinged-clamped beam, which is subjected to a concentrated load, is considered analytically. The problem is formulated based on the inverse variational principle, and the shape that gives the mininum displacement at the loading point among shapes with the same volume is determined. The problem is reduced to one that yields the position where the sign of the moment changes. Although the equation is nonlinear, it can be solved by introducing an intermediate variable. It is shown through the solution of this equation that there is no optimum solution when the load is on the side of the clamped end.

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Shear-bending buckling, induced through seismic excitation, is one of the most important problems in FBR main vessels. The buckling analysis of thin-walled shell structures has always been a difficult problem due to large discrepancies between buckling loads predicted computationally and those experimentally observed. The purpose of this paper is to describe the computation results and the buckling analysis strategy, based on the results of buckling tests and analyses. Available elements and codes, mesh division, modeling of shape imperfections, material property and other topics are discussed. These investigations show the numerical analysis can be a useful tool for estimating the buckling phenomena.

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The failure behavior of symmetric angle-ply laminates under a uniform axial strain was elucidated with special emphasis on the effects of the stacking sequence and fiber orientation. Three basic failure modes, fiber breakage, matrix failure and delamination, are considered. Failure criteria are established in term of quadratic stress polynomials according to the three basic failure modes. The variations of the stress distributions near the free edges are illustrated through the application of a quasi-three-dimensional FEM with a four-node rectangular element. On the basis of the proposed failure criteria and the postfailure analysis, the failure modes are distinguished, the progress of failure to final laminate failure is traced, and the ultimate strength of laminates is obtained. A good agreement is obtained with experimental results found in the literature.

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Mullite composite ceramics contaning 20vol. % dispersed SiC particles (0. 12-1. 71μm) were prepared by hot-pressing at 1650°C under 35MPa for 4h. The effect of dispersed particle size on mechanical properties was investigated. Grain growth of mullite was prevented by the existence of dispersed SiC particles in the matrix, and the matrix grain size of mullite/SiC composites decreased with decreasing dispersed SiC particle size. As a result, bending strength for most mullite/SiC composites increased with decreasing dispersed particle size. In the case of mullite/SiC (0. 56μm), bending stregth showed a maximum value of 626MPa, which was about 60% higher than that of monolithic mullite. The influence of atmosphere of thermal treatment on bending strength of mullite/SiC composites was also investigated. It is concluded that the strengthening by thermal treatment in air was caused by healing of surface flaws in the specimen.

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This paper describes a study on a method of X-ray stress measurement for the nondestructive determination of the gradient of macro- and micro-residual stress components in the surface layer of composite materials. The theory is explained in the first part of the present paper. An experiment on the application of the present method to a two-phase stainless steel prepared by down-cut grinding is described in the second part. The stress gradients of phase, macro- and microstresses in both α-and γ-phases were evaluated by means of the present method under the assumption of linear stress gradient. The theory was introduced under consideration of the effects of finite thickness and a nonlinear stress gradient of a type of polynomial function in order to analyze composite coatings as well as materials with a nonlinear stress gradient.

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The strength of woven fabric composite materials depends on their microstructural geometry. However, the conventional methods for mechanical analysis, which have been widely used to date, are insufficient because they cannot take into account the three-dimensional microstructure. In this study, the three-dimensional homogenization method is shown to be effective for determination of the material constants, microscopic stresses and strength. It has been found that the transverse stress in the lamination direction plays an important role in the fracture of both the fiber bundle and the resin. Also, the effect of the mismatched lay-up on the strength has been investigated. It was predicted that the mismatched lay-up causes a reduction in strength and a difference of crack initiation in the resin. These simulations provide a new concept for the microstructural design of composite materials.

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A system for designing the stacking sequence of a laminated plate by using an object-oriented programming system was presented in this paper. In this system, not only stiffness of a laminated plate but also its strength was considered simultanuously based on a normalized objective function for optimization. The system uses two optimization methods. One is called the sequential decision process and the other the branch and bound process. These two methods were tested and compared. As a result, the sequential decision process was found to be excellent for an actual design process. However, large variation of the stacking number with small variation of applied load was observed in the sequential decision process. To avoid this, a new approach was proposed and shown to be excellent.

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The effect of phosphorus-doping on crystallization-induced stress of silicon thin films is discussed experimentally. Amorphous silicon thin films are deposited on thermally oxidized silicon substrates using chemical vapor deposition. Phosphorus is doped to the film during film deposition. The initial residual stress of the phosphorus doped films is constant at -200MPa, regardless of dopant concentration. The internal stress of the films changes to tensile stress of 800MPa during crystallization due to film shrinkage. Although the magnitude of the stress change is independent of the dopant constant, crystallization temperature of the film decreases with increase of the dopant concentration. The doped phosphorus at the film/substrate interface affects the crystallization process, i. e., structure and crystallinity of the film, of the silicon thin films. The substrate material also affects the crystallinity and crystallization-induced stress of the film.

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Friction and wear of contact surfaces during rolling and sliding should be predicted precicely and then controlled well to achieve high-technology in any kind of industry. Recently, materials has been coated with ceramics to decrease the damage sustained in rolling-sliding contact. However, the effect of coating with ceramics on wear has not been examined thoroughly. In order to analyze the cyclic plastic deformation in repeated rolling-sliding contact, it is necessary to used the constitutive model for cyclic plasticity. In this paper, we attempt to analyze the effect of coated layer on the mechanical behavior of substrate under pressure high enough to cause yielding. The distributions of stress and strain at the layer-substrate interface were discussed in details.

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This paper presents the study of the effect of surface hardening treatment on the wear characteristics of the hardened steel for rolling contact problem. The surface hardened steels have been studied in many papers, but the analysis that treated rolling-sliding contact with FEM is scarcely found. The wear characteristics of the contact surfaces during rolling and sliding should be predicted precisely. We have calculated the deformation, equivalent plastic strain, residual stress, and shear stress-strain curve at the treated area of the steel. It is found that the deformation of treated steel is smaller than that of not-treated steel. And it is the same as in the case where the friction force exists.

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Two-dimensional elastic/viscoplastic stress waves in a semi-infinite stepped bar are analyzed numerically, when torsional impacts are applied to the end face of the stepped bar. For the numerical analysis, a finite difference method along the bicharacteristic is employed. By examining the distributions of maximum tensile stress arising in the vicinity of the junction of the stepped bar, influences of the stepped bar shape and loading condition on stress concentration are investigated. It is also found that the maximum tensile stress is at the corner of the stepped bar for every numerical condition.

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Mechanical properties of tetragonal zirconia polycrystals are examined in terms of deformed strain and grain size after superplastic compression at 1 500°C, and the mechanisms of microstructural contribution are elucidated. The specimens for mechanical tests are obtained from block specimens deformed at various strain rates and stopped in different strain states. The bending strength and Young's modulus increase with strain but show no dependence on the grain size. The reduction of flaw size due to compressive strain is expected to be a primary mechanism of enhancement. The Vickers hardness represents the softening behavior at the initial deformation and cannot be evaluated from either the strain or the grain size only. On the other hand, the change in the fracture toughness is evaluated by the grain growth behavior. The fracture toughness increases with grain size due to the increased transformation-zone size near the Vickers indentation.

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The optimum shot peening condition to improve fatigue strength for automobile transmission gears was investigated. Motion and clashing of shot particles were quantitatively described in relation to gear shape, and correlation with residual stress was investigated. Based on these results, computer simulation techniques for optimizing the shot peening conditions were proposed using the correlation between the fatigue strength and the residual stress which had been obtained in the previous work. Experimental results on the fatigue strength of gears coincided with the analytical prediction.

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This paper deals with the algorithm of structural analysis by the E-method for a three-dimensional multistoried and multispan rigid frame with circular members loaded in arbitrary directions, in which the bases of all columns are fixed. Revolution angles and axial forces of individual members are taken into consideration and the digital computing program based on this method is developed. The fluid coordinate system is used here to establish the basic formulae. At the end of the paper, the results from an example are given.

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The metastrategy to solve discrete optimization problems is proposed and discussed. The proposed solution procedure is based on the genetic algorithm, GA, in which the idea of simulated annealing, SA is introduced effectively. The procedure has a distinctive feature that the number of generations can be reduced by introducing the idea of the variable mutation ratio in GA based on the annealing schedule of temperature is SA. Applicability is examined with the shape of the optimization problem of the truss structure subjected to three kinds of constraints on homologous displacement, the first eigenfrequency and minimum weight.

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The trabecular system is a useful source of knowledge for the mechanical environment of bone, which is important in orthopedic treatment. This study proposes a method for the estimation of loading conditions on bone structures, by using bone data and FEM analysis. In this paper, the loads on the femoral head are estimated based on two measures. One measure is the difference between distributions of equivalent stress and apparent density, and the other measure is those between principal direction and traveling direction of trabeculae. Equivalent stress and principal direction are calculated by the finite-element method, and apparent density and traveling directions of trabeculae are estimated using the image processing technique. It is found from the results of both methods that the loads on the femoral head in the frontal plane are similar to those which are estimated from Pauwels' theory. This result shows that trabeculae have functional adaptability, and unknown loads applied to bone may be estimated using the inverse finite-element mothod.

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This paper describes a cellular automaton that generates a topological structure for a loading condition. The mathematical model is based on the remodeling (functional adaptation) of biological systems. The model consists of same cells which are mechanically connected with each other. Each cell changes its Young's modulus during sensing of mechanical states around it. Computer simulation showed that the cellular automaton generates many topological structures under the same boundary conditions by changing the distribution of the initial Young's modulus. In order to estimate these topological structures, we proposed a diagram that evaluates the mechanical performance by positioning the structures on a plane with two axes along maximum stress and maximum displacement. The diagram gives us a perspective concept for the design of topological structures.

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To investigate the effects of stress frequencies and bone density on the fatigue lives and crack growth behaviors, rotating bending fatigue tests on bovine compact bone were performed under various stress frequencies ranging from 0.3 Hz to 30 Hz. Cycle-dependent features were observed in the fatigue behavior of bovine bone within the above range of stress frequencies. This result differs from the previous findings that fatigue lives increase with stress frequency in the range above 30 Hz ; therefore in bone fatigue tests, it is wrong to estimate fatigue behaviors at lower stress frequencies from those obtained at higher stress frecluencies. The fatigue lives and the crack initiation time for the bone specimens were expressed as functions of both the applied stresses and the bone density. l These expressions may be useful for predicting the time when cracks may be induced in bone by daily activities.

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The compressive deformation behavior of normal and degenerated cancellous bones is visualized during a static compression test. The normal principal compression trabeculae are broken, owing to flexural buckling. The osteoarthritic process results in a change of the cancellous structure. That is, the ratio of thickness per unit length and the ratio of thickness per unit width of the principal trabeculae increased by degeneration. Because the degenerated principal trabeculae increase buckling resistance, fracture occurs owing to stress concentration at the node of the individual trabecula. The degenerated cancellous bone exhibits only the constant deformation resistance without the flexible deformation that would adjust to the change of loading in a hip joint.

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Ultrahigh-molecular-weight polyethylene (UHMWPE) is the material generally used for the articular plate contact surface in artificial knee joints ; however, the wear of this material becomes a serious problem during extended life of the joint. In order to understand the wear mechanism of the plate during gait and to improve its wear life, the cyclic contact behavior of the plate was analyzed using the constitutive equation for cyclic plasticity, since the plate is subjected to cyclic contact deformation during gait. The posterior cruciate ligament (PCL) retention-type artificial knee joint as the basic analytical model, as well as two other modified contact surface models, were analyzed to investigate the effect of the shape of the contact surface on the wear behavior of the plate. As a result, it was clarified that the wear behavior of the plate is closely related to the shape of the contact surface. The optimal design of contact surface is considered using this analysis.

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Properties of electromagnetic acoustic transducers (EMATs) for S₀ mode Lamb wave are experimentally studied. The EMAT, which consists of a meander coil and an electromagnet, can transmit and receive the S₀ wave in a thin metal plate effectively. When the EMAT is applied to nonmagnetic materials such as aluminum alloys, the excitation mechanism relies on the Lorentz force, which is a product of the interaction between the induced eddy current and the static magnetic field. The amplitude of the S₀ wave is thus proportional to the static field strength. When used with ferromagnetic materials such as steel, the S₀ wave is generated mainly by magnetostriction, while contribution of the Lorentz force is negligibly small, especially in the low-field region. In this study, two types of EMATs, one applying a horizontal magnetic field and the other a vertical field, are used for the aluminum sheet and the low-carbon steel sheet. The results turn out to be in good agreement with the above prediction. The horizontal field type EMAT is proved to be suitable for the ferromagnetic materials, while the vertical type for the nonmagnetic materials.

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