Fatigue tests in the low-cycle range had been performed to investigate the fatigue crack initiation characteristics under a completely reversed push-pull load. The material used in this test is high manganese content austenitic steel (HM steel) in comparison with a typical austenitic stainless steel SUS304. Then, it is confirmed that there are no differences in the fatigue crack initiation and the relatively small crack growth properties, and that the Manson-Coffin law can be applied to these two kinds of materials. In addition, the gradient in the relationship between the plastic strain and the number of cycles under the strain-controlled condition becomes larger for HM steel than that for SUS304. On the other hand, HM steel shows the same properties as SUS304 in the relation between the cumulative plastic strain and the number of cycles to failure not only under the strain-controlled condition but also under the stress-controlled condition.

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In order to investigate the effectiveness of high-temperature proof testing in silicon nitride, static fatigue tests at l000°C were conducted using the specimens with and without proof testing at l000°C. The experiments were conducted in air under four-point bending. The times to failure of survivors of proof testing were measured and compared with that of as-received specimens, and the relation-ship between the proof-testing effect and the proof-testing conditions was investigated. It was clarified that high-temperature proof testing was influenced by oxidation of specimen surface and loading rate of proof stress.

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Fatigue properties of T300/#3631 graphite/epoxy laminates subjected to constant-amplitude compressive and tensile-compressive loading were examined. Strip-type specimens were used and the stacking sequences of the laminates were [(0/90/+45/-45)_n]_s and [(+45/0/-45/90)_n]_s. Out-of-plane deformation of the specimens were observed for compressive loading following delamination at the free edge of the specimen. In order to consider the fatigue life estimation method based on delamination onset, at first initial crack length was assumed. Measured nominal strains of [+45₃/0₃/-45₃/90₃]_s and [0₃/90₃/ +45₃/-45₃]_s laminates and calculated energy release rates were used to predict initial crack length at the free edge. Secondly, the relationship between calculated ΔG at the initial crack length on the delamination interface and the measured delamination onset cycle was obtained. It is shown that the use of these results can be effective in predicting the fatigue life based on the onset of delamination.

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A new combined process for improving the fatigue strength of carburized steels has been developed. This process consists of two treatments : shot peening and chemical polishing. Shot peening yields a high compressive residual stress near the surface of a workpiece, and chemical polishing removes the oxidized and nonmartensitic layer which is harmful to fatigue strength. Since the chemical polishing by the developed solution of 1 mol/l HF and 2 mol/l H₂O₂ can be conducted by immersing the workpiece in the solution, it is easy to treat complex shaped workpieces. Furthermore, a smooth surface and high compressive residual stress are obtained by treating with chemical polishing after shot peening. The factors of increase of fatigue strength by means of the new combined process for carburized notched specimens are l.76 on the notch radiusρ= 0.5 mm, 1.63 on ρ=1.0 mm and l.51 on ρ=2.0 mm.

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Rotating bending fatigue tests had been performed to investigate the effect of carbon content on the characteristics of fatigue crack initiation, using four kinds of high-manganese steels with carbon content between 0.025%-0.10%. Although there exist nonpropagating cracks in HM steel (0.178% carbon) under the fatigue limit of l0⁷ cycles, these cracks are not observed in four kinds of HM steels (0.025-0.1% carbon) under the stress of each fatigue limit by l0⁷ cycles. From this, the limit of existence for nonpropagating cracks is concluded to be between 0.1%∼0.2% of carbon content, and the characteristics for crack initiation under the fatigue limit of l0⁷ cycles are founded to be prodominantly influenced by the carbon content.

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The in-plane bending fatigue tests were carried out on FCD 450 at elevated temperatures up to 723 K. The threshold stress intensity range ΔK_th and its effective values ΔK_effth were observed as a function of the temperature T. Plots of ΔK_effth and T revealed that ΔK_effth remained constant up to 623 K and then decreased to a value about 28% lower at 723 K. The ΔK_th-T relations showed that ΔK_th remained constant in the range of 473 K to 723 K, its value being about l0% lower than that at room temperature. While the ΔK_effth value at 723 K decreased by 28% lower than that at 623 K, there were no significant differences between the ΔK_th value at 723 K and that at 623 K. It appears that the rise of closure level K_cl induced by the high-temperature oxide on fracture surface results in the apparent increase in ΔK_th value at high temperature such as 723 K.

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The effect of silicon carbide #(SiC) on the fatigue crack propagation behavior of A6061-T6 metal matrix composites reinforced with 10 vol. % or 20 vol. % SiC particles of various diameters was investigated. In general, in the range of low stress intensity factor, fatigue cracks propagate in the matrix, avoiding the particles, addition of the particles improved the crack propagation behavior of the composite, and the crack propagation rate was decreased with decreasing mean interparticle spacing. However, at the higher stress intensity factor range, subcracks were formed in front of the fractured particles by the stress concentration and these subcracks coalesced with the main crack, which increased the overall crack propagation rate.

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Fatigue strength and fracture mechanism of ceramic/metal (Si₃N₄/Cu/SUS 304) joints were investigated under cyclic bending loading. Results showed clearly the characteristic of the cyclic fatigue, and the fatigue strength at l0⁷ cycles was about one-half of the static bending strength. Different types of failure were observed for low-cycle and high-cycle fatigue regions. In the low-cycle fatigue region, the crack initiates at the copper interlayer near the interface of the ceramic side, while in the high cycle fatigue region the crack initiates throughout the entire copper interlayer. Fracture surfaces were examined by SEM and EPMA. Fatigue striations were clearly identified. 0n the basis of these results, a model is suggested for the fracture mechanism. The crack initiates and grows at the copper interlayer and finally kinks to the ceramic side. It is concluded that the copper interlayer dominates the fatigue strength of the joint.

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Fatigue crack propagation behavior under the mixed-mode condition which combined modes I and III and modes I, II and III was investigated in a push-pull fatigue test of notched specimen. The notch inclined in the thickness direction was cut at the center of the specimen. Four values were selected for the notch length 2b, that is, 2b=9, 15, 25, 35 mm. In the present study, the crack propagation behavior under the mixed modes is assumed to be dominated by the maximum principal stress criterion. The stress intensity factor K_p of mode I was calculated with the projected crack length along the load direction and the crack propagation rate da/dN under the mixed modes was evaluated using it. This stress intensity factor K_p can approximate relatively well the stress intensity factor determined on the basis of the maximum principal stress criterion in the case of the specimen used in the present experiment. The crack propagation rate da/dN can reasonably be evaluated with the effective stress intensity factor range of K_p independent of the applied mean stress.

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Influence of weathering on fracture toughness (J_c), microhardness (H_μ) and ultrasonic velocity (V_r) in unfilled and short-glass-fiber-filled polyester, Xenoy, has been investigated. The materials were weathered outdoors in Perth, West Australia. The specimens weathered for 6 months showed a slight increase in J_c as compared with unweathered specimens. Weathering for 11 months caused a large decrease in J_c and a slight increase in yield strength. Fracture surfaces of the specimens, however, exhibited little difference. 0n the other hand, H_μ measurements revealed a feature consistent with the trend of J_c. V_r decreased considerably in the surface layer weathered for 11 months. Weathering by artificial ultraviolet rays induced a strong increase in H_μ and a small decrease in V_r. Consequently, it was shown that the measurement of J_c in combination with H_μ and V_r is an effective way of studying weathering effects for thermoplastics.

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The influence of microstructure on the growth behavior of small fatigue cracks in dual-phase steel was investigated using about fifteen plain specimens for each stress level under rotating bending. The minimum crack length above which the small-crack growth law (dl/dN=Cl) is applicable was evaluated statistically. The small-crack growth law holds in most growth process, including the range where the crack growth rate fluctuates due to the influence of microstructure, provided mean crack growth rate is considered statistically. That is, the minimum crack length for the application of the growth law is nearly equal to the initial crack size. Therefore, the scatter of the crack growth rate and the distribution of fatigue life can be evaluated through the statistical properties of the value of C.

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For hydrogen-assisted cracking of 2.25 Cr-1 Mo steel, the evaluation of the threshold stress intensity factor for subcritical crack growth was examined by employing the slow strain rate test. Also, by the method of recrystallization, a high strain region formed at the crack tip was observed, and the effect of hydrogen on plastic deformation was studied. By this experiment, it was shown that hydrogen promoted subcritical crack growth at a low stress intensity level, K_IH(40∼80 MPa·m^1/2)well below K_Ic(300∼400 MP·m^1/2, and hydrogen also enhanced plastic deformation at the crack tip. This result suggests that the plastic deformation which is enhanced by hydrogen exerts large effects on subcritical crack growth in hydrogen-assisted cracking of 2.25 Cr-1 Mo steel.

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The finite element method was applied to a generation phase analysis for stable crack growth in inhomogeneous materials. Experimental data on stable crack growth in bimaterial CT specimens, which were cut from a weldment of a A 533 B Class 1 steel and a HT 80 steel plate, were numerically simulated using the node-release technique to obtain the variations of the fracture mechanics parameters such as J-integral, T^*-integral, J-integral and CTOA. New evaluation schemes for the integral parameters were proposed to be valid for integral paths passing a fusion line of dissimilar materials. It was examined whether simple estimation schemes of the J-integral for a monolithic CT specimen can be applied to a bimaterial CT specimen or not. The effect of inhomogeneity on the fracture mechanics parameter was discussed in terms of the Q-factor.

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In this study, the location and the size of the three-dimensional semi-elliptical surface crack in a semi-infinite body, and the loading stress at infinity are determined on the basis of the data of strains measured around the region of the crack. In searching for the location and the size of the surface crack, the method of gradient search is employed which minimizes the sum of the squares of the residuals between the measured strain distributions and the computed ones for the assumed crack location and size. The body force method is used to calculate the strain field around the crack. In order to obtain the solution with short CPU time, the crack is represented by several concentrated force doublets ; moreover, the database of the magnitudes of force doublets for various aspect ratios of the crack is utilized. Based on the fact that the strain field around the surface crack is mainly dominated by the crack area, the crack area and the aspect ratio are chosen as parameters and several inversion schemes are examined to obtain accurate results. Numerical simulations are carried out and the results show that the location and the shape of the crack are determined efficiently and with good accuracy.

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It has been shown that, in a mixed-mode crack, not only mode I (opening type) fracture but also mode II (shearing type) fracture can occur under some loading condition. Therefore, we previously proposed the fracture criteria for mode I and mode II fractures based on the CED (crack energy density) in an arbitrary direction, ε_ψ, with the criterion for judging the fracture mode. In this paper, at first, based on the above fracture criteria, the relation of the fracture mode to loading type in an elastic mixed-mode crack is discussed, changing the loading type in the neighborhood of a crack tip represented by stress intensity factors K_I and K_II from mode I to mode II continuously. Subsequently, the influence of plastic deformation on the fracture mode is also discussed based on the change of ε_ψ with the increase of plastic deformation. Moreover, through comparison between the results of fracture experiments of the specimen with an inclined crack under tensile type loading and the corresponding results predicted by the criteria, the influence of plastic deformation on a fracture accompanied with small scale yielding is studied.

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Monotonic tensile tests were carried out on unidirectional CFRP to clarify the effects of specimen configuration on fracture mode and tensile strength. Three types of specimen configuration, a standard specimen according to JIS, necked-on-width specimen and necked-on-thickness specimen having various thicknesses of the necked region, were used. The following results were obtained. (i) A transition in fracture mode from tensile failure at the necked region (fracture mode type A)to interlaminar shear failure spreading to the outside of the necked region before final fracture (fracture mode type B) was observed in the necked-on thickness specimen as the thickness ratio of necked and un-necked regions increased. Fracture mode type A occurred when the ratio was low because the tensile failure load was lower than the shear failure load, and high thickness ratio resulted in fracture mode type B due to increasing tensile failure load over that of the shear. (ii)The specimen which fractured with shear failure exhibited lower tensile strength than the specimen which fractured in the tensile mode at the necked region.

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The stress and strain in very thin film under uniaxial tension are analyzed through the motion of particles constructing the film by means of two-dimensional molecular dynamics simulation. The Lennard-Jones-type potential is assumed as a two-body potential. The tensile load is applied by elongating the longitudinal length of the fundamental cell. The numerical results show that the stress decreases considerably with the decrease of the size of the region, defining it when the size is small. It is found that more than 130 particles are necessary for the stress concept used in continuum mechanics.

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The stress singularity and stress intensity factor around a corner point of a regular polygonal cavity or a regular polygonal rigid inclusion under in-plane and out-of-plane loadings are examined. The analysis is based on the complex variable method using the conformal mapping technique. Numerical results are agreed with those of other investigators for the particular cases of our solutions.

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Rotating bending fatigue tests were carried out on plain speciments of ferrite-pearlite steels and ferrite-martensite steels in order to investigate the influence of microstructures, especially ferrite grain size, on the coaxing process. The coaxing effect of a ferrite-martensite steel is larger than that of a ferrite-pearlite steel. Furthermore, in both steels the coaxing effect is greater when the grain size is small.

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In order to investigate the influence of microstructure on the coaxing effect, rotating bending fatigue tests were carried out on plain specimens of two kinds of dual-phase steels, Steel A which has a microstructure containing isolated martensite phases in a ferrite phase and Steel B which has a continuous martensite phase filled with ferrite phase. In both steels, nonpropagating cracks were observed at their fatigue limits and the tips of the nonpropagating crack initiated in a ferrite phase or near the phase boundary were blocked from growing by martensite phases. Moreover, the origin of final fracture in coaxing process was the nonpropagating crack initiated at the first stress level. The coaxing effect was more marked in Steel B than in Steel A. The reason was discussed based on the difference in the crack growth path caused by the martensite morphology, that is, the cracks blocked by martensite structures changed the direction of growth and propagated through ferrite structures in Steel A and the cracks in Steel B penetrate the martensite structures.

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The effect of strain rate on the plastic deformation behavior of austempered spheroidal graphite cast iron was studied. The matrix of specimens consisted of mixed banitic ferrite together with retained austenite. Thin-walled tubular specimens were strained under tensile stresses or torsional stresses. It was found that the deformation of austempered spheroidal graphite cast iron under both tensile and torsional stresses did not depend much on strain rate in an elastic region. The results for maximum strain under tensile stresses were scattered because the specimens were thin-walled tubes which had numerous graphite nodules and a few defects. The results of tensile tests of thin-walled tubular specimens were greatly influenced by the shape of specimens and defects, whereas the results of torsional tests were hardly influenced. The ratio of transformed retained-austenite into martensite under torsional stresses did not vary with strain rate. It was presumed from this result that work hardening affected an increase of yield stress and torsional strength.

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A finite-element polycrystal model proposed by Takahashi [Int. J. Plasticity, 10 (1994), 63. ]where each element in FEM is assumed to be a crystal having different orientations is applied to 3-dimensional plastic deformation analysis of ear in deep drawing and texture in extrusion. The crystal orientations are determined from the pole figures obtained by X-ray diffraction. The calculated results for FCC metal are compared with the experiments for aluminium and these results almost agree. Even though the number of crystals is limited due to the computational cost, the predicted features are appropriate for practical use.

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This paper describes a numerical analysis method for multiobjective shape optimization problems of linear elastic structures. For an example, we treat a multiloading mean compliance minimization problem with a volume constraint. The presented method is based on the traction method that was proposed as a solution to the domain optimization problems by one of the authors. The traction method is implemented to analyze the speed field, which represents the domain variation, with regard to the deformation field of the linear elastic continuum formed in the objective domain applying the force in proportion to the shape gradient function. To scalarize the multiobjective functionals we employ the weighted l_p-norm method with four types of norms. The shape gradient functions for each scalarized objective functional are obtained using the Lagrange multiplier method. For the numerical analyses we used a general-purpose finite-element code. Numerical results to a multiply connected plate problem and to a solid structure problem under the multiloading conditions show the validity of the present method to obtain practical Pareto solutions.

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We first predict using the elementary beam theory that a loading system of asymmetrical four-point bending (AFPB) applied to a beam produces a pure shear loading state through the middle section of the beam. For further investigation, we attempt a detailed analytical study of the stress state in a beam of infinite length subjected to AFPB loading system within the framework of the two-dimensional elasticity theory. The stress function approach is employed, and the principle of the superposition and the method of Fourier transforms are also used in the analysis. The numerical calculations are carried out for the stress components associated with a pure shear stress field.

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In this study, the energy release rate derived previously and the method to determine the debonding length are applied to the cohesive force model that treats bridging fibers as a distribution of stresses to close the crack face. A numerical method to solve the cohesive force model of a penny-shaped crack is provided to determine the bridging stress, the debonding length, the crack opening displacement and the stress intensity factor. By introducing the fracture criteria of the composite and fiber, R-curves for the penny-shaped crack are simulated and the effects of such parameters as interface fracture toughness, compressive residual stress, frictional sliding stress, and fiber volume fraction on the R-curves are clarified. Based on the R-curve results, the toughening mechanism of FRC is discussed.

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An incremental theory is developed to describe the elastic-plastic behavior and damage behavior of particulate-reinforced composites, based on Eshelby's (1957) solution of an ellipsoidal inclusion and Mori and Tanaka's (1973) concept of average stress/strain for a finite concentration of particles. In the composites containing hard spherical particles in a ductile matrix, debonding of the particle-matrix interface is a significant damage process, as the accumulation of the debonding damage affects the deformation and strength of the composites. The debonding damage is assumed to be controlled by the stress of the particle and the statistical behavior of the particle-matrix interfacial strength. During debonding, the stress of the particle is released and the site of the particle is regarded as a void, resulting in a void concentration increasing with deformation. The theory describes not only the reinforcing effect due to the intact particles but also the weakening effect due to the damaged particles. Analysis of the stress-strain response under uniaxial tension has been carried out on the particulate-reinforced composite based on the present theory. The influence of the damage on the stress-strain relation of the composite is very drastic and depends on the statistical properties of the particle-matrix interfacial strength.

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In this study, an attempt to analyze the creep cavitation in Cr-Mo-V rotor steel based on probability theory or statistical mechanics was made. The following were obtained as the conclusions : a) Grain-boundary sliding which induces creep cavities may show an exponential distribution. b) "A" parameter data of Cr-Mo-V rotor steel may show a binomial distribution B(n' ; M', p), where n'=INT(A×M'+0.5), INT(x) is the maximum integer which is not larger than x, A=n/M, n is the number of damaged boundaries and M is the number of observed boundaries. The mean value of the distribution p is p={(t/tr)/(t/tr+k')}×exp{-C'/(t/tr)}, where t/tr is life fraction. The values of k', C' and M' shound be determined by the maximum likelihood method.

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A numerical method to analyze three-dimensional dynamic thermal stresses in a semi-infinite plate is presented, in which instantaneous heating is applied to part of the plate surface. For the numerical analysis, the finite difference method based on integration along bicharacteristics is employed. From the numerical results, it is found that the propagation and reflection of the stress waves under instantaneous heating can be examined in detail by this method.

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The present paper discusses a transient thermoelastic problem in a transversely isotropic infinite cylinder containing a flat circular rigid inclusion, in which axisymmetric heating is subjected to the lateral surface of the cylinder. The method of successive approximation as well as the Fourier integral and the Bessel series are used to satisfy the boundary conditions of displacement and stresses. Numerical calculations of the stress singularity coefficient at the tip of the inclusion are carried out for a transversely isotropic graphite and compared with those derived under isotropic conditions.

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Buckling tests for cylinders with a thermal ratchetting deformation similar to the elephant-foot-type buckling mode in bending were carried out to evaluate the effects of this type of imperfection on buckling strength in bending. Test results show that the degradation of buckling load for cylinders with thermal ratchetting deformations is rather small because of the material hardening accompanied by the progress of ratchetting deformation. Numerical analyses considering material hardening and ratchetting deformation show that the above mentioned test results can be explained analytically, and that the degradation of buckling load without material hardening is nearly the same as the effects of axisymmetric geometrical imperfection on buckling strength in bending.

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All atomic force microscope (AFM) possesses two excellent potentials of atomic scale imaging and nanofabricating. Applying these two potentials, a nanoindentation technique was developed. The hardness measurements were carried out for cementite - spheroidized S25C steel (Vickers hardness HV=128) and 400°C-tempered SNCM439 steel (HV=414), using a cantilever with three-side-pyramidal diamond tips. The depth of indentations created was between 14 and 330nm. The difference in hardness between S25C and SNCM439 steel was detected in the nanoscopic region. It was concluded from these results that the nanoindentation was realized with AFM.

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This paper presents a new method to measure surface strain without contacting specimens using metal foil gauges assisted by the laser speckle method. If a metal foil (such as aluminum, copper or nickel) is pasted on a specimen and the specimen is loaded cyclically, slip bands are produced on the metal foil by fatigue. The occurrence of the slip bands is dominated by the strain amplitude of the specimen surface and the number of loading cycles. There is a direct relation between density of the slip bands and the strain amplitude or loading cycles. Thus the surface strain can be estimated by observing the surface change. The method presented in this paper involves non-contact strain measurement by the application of the speckle technique for detection of the surface change due to occurrence of slip bands. In this experiment, aluminum foil was used and the result showed that it is possible to detect surface change of the foil surface by cyclic loading using the laser speckle method and there is a direct relation between speckle intensity distribution and loading cycles under constant strain amplitudes. It is also possible to estimate surface strain by observing the distribution of laser speckle intensity.

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Hydraulic tensioners are widely used in tightening important structural members such as large-scale diesel engines and pressure vessels. The ratio of desired clamping force to initial tension, which is termed the effective tensile coefficient, is the most important factor to be predicted in the actual operation for given joint configurations. In this paper, an elementary approach to estimate the coefficient, taking the effects of contact stiffness into account, is proposed using spring elements. The influences of contact stiffness of four contact surfaces on the coefficient are discussed, and it is concluded that stiffnesses of pressure flank of threaded region and bearing surface of nut would be the factor deciding the coefficient.

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In order to solve the effect of the surface pretreatment of a substrate on nucleation, numerical simulation of the nucleation of diamond on silicon substrate by the CVD method was conducted. Diamond thin film has been confirmed to be connected to the substrate by only the nuclei grown at the beginning of deposition. Therefore, in fabricating diamond thin film, it is important to increase the number of nuclei, namely, nucleation density. The fact that nucleation density on a pretreated substrate is much higher than that on substrate without pretreatment is known empirically, but its mechanism has not been established. In this paper, a two-dimensional nucleation model that consists of a pretreated silicon substrate and reaction gas was proposed. Scarring on the surface of the substrate introduced by surface pretreatment was modeled by a V-shaped notch having two point dislocations. The model was verified by performing numerical simulation of nucleation.

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We throughly observed fracture surfaces of austempered ductile iron (ADI) cylinders which fractured in the very high cycle region under internal pressure fatigue tests by SEM, and investigated the reason for the unique fatigue behavior, i.e. the fracture origins changed from casting defects to small graphite with decreasing applied stress, and the S-N diagram drops again after levelling off at l0⁶∼10⁷ cycles (two drop S-N diagram). As a result, it was clarified that (1) ADI has special spheroidal graphites which have the possibility to induce stress concentration on the micron order because of the wedgewise precipitation of carbon into the ferrite layer at the interface of graphite and matrix ; (2) at low stress levels, there exists a highly structure-sensitive crack propagation initiated from this type of spheroidal graphite, and its crack growth rate is estimated to be very low compared with that at high stress levels ; and (3) the "two drop S-N diagram" is caused by both phenomena that cracks from casting defects are arrested and that the propagating mechanism of (2)appears at low stress levels.

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The three-dimensional mesomechanical simulation method previously proposed by the authors for brittle microcracking solids is extended to include the effects of microinclusions. The relationship between overall elastic moduli and total volume fraction of microinclusions as well as the influence of microinclusions on the microcracking behavior are studied in order to demonstrate the validity of the proposed method.

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In this paper, the problem of finding the best possible distribution of the cross-sectional area of a clamped-clamped column with two inside hinges, which for a given volume would have the highest buckling load, is solved. The general formulae for clamped-clamped columns with two inside hinges are presented and verified with examples, with which optimization problems with respect to both global and local buckling modes are investigated. It is found that the column obtained by Olhoff and Rasmussen, whose shape is optimized with respect to the nonsymmetrical global buckling mode, has much lower buckling load than that optimized with respect to the nonsymmetrical one under rigid-body rotation buckling mode in which the buckling takes place only in the two end parts of the column. The true optimum solution is obtained by simultaneously considering the rigid body rotation buckling mode and a local buckling mode in which buckling occurs only the central part of the column.

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It is difficult to obtain a global solution on a homologous truss structure using the traditional gradient-based algorithms, because it is a complicated combinatorial problem. In this paper, a technique to obtain homologous truss structure using a genetic algorithm (GA) is proposed. Namely, the structural arrangement and node coordinates are considered simultaneously with the design parameters. The homologous feature and other mechanical character of the structure are expressed as one objective function to obtain its minimum value. This technique is applied to a six-node truss. From the results, it is obvious that the proposed method is efficient and the layout problem of a homologous structure is a very complicated combinatorial one.

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The efficiency of visual biofeedback (VFB) training method using a Photoelastic imaging system on restoring and stabilizing a standing position of stroke patients was investigated. As a stroke group, seven hemiplegics were selected with the mean of 57 year-old. Twelve age-matched healthy subjects were selected as controls. The subjects were asked to stand upright on the photoelastic apparatus and to gaze at a marker 1.5M distant on the wall. Then, VFB training was performed for ten minutes by self recognition of his own pressure patterns which were produced by photoelastic system and were monitored on a TV screen. The patterns were photographed in each different condition such as in a standing position with eyes open or closed before and after l0-minute-training with VFB, and were comparatively analysed. The results showed that (1) the ratio of affected side to unaffected definded by the number of first fringes produced increased significantly after VFB up to the control level, (2) the ratio of body weight loading on the affected side to unaffected was significantly increased after VFB, and (3) the position of center of contact pressure on the longitudinal axis of an affected sole was found to be significantly more posteriorly sifted than in the control and was remained unchanged after VFB. In conclusion, the VFB method using a photoelastic imaging system may be useful to enhance visual-contact motor balancing functions in patients with hemiplegics and also to study a restoring process of neurological impairment leading to a postural problem.

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Ultrahigh-molecular-weight polyethylene (UHMWPE) is used for the material of the contact surface in artificial knee joints, but the wear of this material becomes a serious problem to extend the life of the joint. In order to understand the wear mechanism of the UHMWPE in gait movement, the cyclic contact behavior of the UHMWPE is analyzed using the constitutive equation for cyclic plasticity because the UHMWPE is subjected to cyclic contact deformation during gait movement. In this analysis, the contact pressure distribution which is determined from the simple indentation analysis of femoral and tibial components is translated on the UHMWPE, changing its value so as to simulate the realistic movement of the joint. For the analytical model, the posterior cruciate ligament (PCL) retention-type artificial knee joint is employed. As a result, it is clarified that local deformation is caused in this artificial knee joint, and the effect of the stress history, to which the UHMWPE has been subjected, on the wear machanism of the UHMWPE is significant.

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The sectional form of the human femur is measured via an ultrasonic pulse echo method. After the wave velocity through the thigh is set at 1500 m/s, the ultrasonic wave is emitted toward the femur using a normal probe attached to the thigh. The echo waveform reflected from the outside and inside of the femur is measured, and the sectional form of the femur presented in two dimensions is compared with that of the X-ray. Consequently, the wave velocities of the femur and the muscle are determined as 3300 m/s and 1560 m/s, respectively. Next, the sectional form of the femur modified by these values, obtained via the ultrasonic method, is compared with that of the X-ray CT. It is found that both results agree approximately. Thus, the ultrasonic method is applicable for the proposed purpose.

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Normal mode analysis of G-actin elucidates the dynamic properties at the molecular level, which should concern the actomyosin contraction motion. In 1990, Holmes published 3-D molecular structure data, determined by X-ray crystalline structure analysis. The minimum energy conformations of G-actin in four cases, with ATP or without ATP, and proK-actin-cut off between Met-47 and Gly-48-or normal actin, were determined by the steepest-descent method and the conjugate-gradient method in the molecular mechanics calculation. The fluctuations of these four actins are studied by the normal mode analysis which is based on the quadratic approximation of the conformational energy function. Root-mean-square atomic fluctuations (r. m. s. fluctuations) reveal the deformability of the conformation at the atomic level. The values of r. m. s. atomic fluctuations of proK-actin are less than those of normal G-actin. This means less functional ability for the actomyosin sliding motion because of less deformability of the 3-D molecular structure. This tendency is suppressed in both cases without ATP. In particular, the existence of ATP exaggerates the fluctuation in the case of G-actin. We also confirm that G-actin with ATP is softer having a higher value of specific volume, than the cases without ATP and with cut-off peptide bonding. We conclude that the softer the actin-e. g., G-actin with ATP-the greater the functional ability for actomyosin sliding motion.

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