Both completely reversed in-plane and out-of-plane bending fatigue tests were carried out at 900°C. The effects of the loading direction and the displacement rate on the deformation of a curved tube under creep-fatigue conditions at an elevated temperature were examined experimentally and analytically. A main crack was observed at the lower side of the elbow in the in-plane bending fatigue tests. In the out-of-plane bending fatigue tests, the main crack was observed at the side of the elbow and extended in the direction 45°to the axis of the test tube. The position and direction of the main crack were in fairly good agreement with those of the analytical results. The inelastic analyses were conducted using two types of the creep constitutive equation. A comparison between the predicted fracture lives based on analyses and the experimental results of the test tubes was undertaken.

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Metal matrix composites are gaining increasing attention in materials research and attracting engineers as a candidate material for future applications. This investigation demonstrates the tensile fracture and fatigue behavior of continuous γ-alumina fiber (Altex) reinforced aluminum matrix composite, i.e., γ-Al₂O₃ (Altex) / Al that was fabricated by a squeeze casting process. Special attention was paid to the environmental influence of vacuum. Fiber reinforcement increased tensile strength, elastic modulus and fatigue strength. At lower stress levels, the fatigue strength of a [0°] specimen at a stress ratio R of -l decreased from that at R = 0.05, because an initiated longitudinal crack promoted microbuckling of fiber at R = -1. However, at higher stress levels, the strength at R = -l equaled that at R = 0.05. The fatigue strength of a [90°] specimen in vacuum was higher than that in air, although the tensile strength was the same. The composite had strong fiber / matrix interfacial strength and therefore, the matrix cracking was dominant in the [90°] specimen, leading to a higher fatigue strength of the matrix in vacuum. In contrast with these, the tensile and fatigue strength of a [0°] specimen was increased in vacuum, because the fiber strength was increased. Single fiber tests showed that fiber strength increased with decreasing water content in an environment and with increasing displacement rate. The mechanisms of tensile and fatigue fracture as well as influences of vacuum were discussed.

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Fatigue tests under axial loadings with mean stress δm were carried out on the specimens of spheroidal graphite cast iron. The initiation and propagation behaviors of microcracks were investigated through successive observations by the plastic replica method. The main results are summarized as follows. (1) The fatigue limits under different mean stresses are always determined by the limiting condition for crack propagation. (2) The crack which leads to final fracture appears from a graphite when δm<0, but appears from a microshrinkage cavity when δm≥0. (3) As the mean stress increases, the fatigue limit decreases considerably because of the above result (2).

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The influence of HIP treatment on the fatigue reliability of aluminum alloy castings was investigated. The main results obtained were as follows : (1) The fatigue strength of HIP-treated castings was improved by 20% ∼ 30% by the HIP treatment. (2) As the cooling rate of HIP-treated castings was increased, the microstructure was controlled fine. The fatigue strength of HIP-treated castings produced using a rapid cooling rate was greater than that produced using a slow coolling rate. (3) According to the S/δ₀.2 N diagram, it could be understood that the fatigue strength of HIP-treated castings was mutually related to the yield strength. (4) The effect of stress gradient on 10⁷ fatigue strength of HIP-treated castings was less than that on non-HIP-treated castings. (5) The plane facet induced by slip was always observed at the origin of the fatigue crack in HIP-treated castings. Hence it could be concluded that the fatigue strength of HIP-treated castings was improved because the porosities were reduced by HIP treatment. (6) From SEM fractographs, it is considered that the fatigue life is controlled by the plane facet size at the origin of the fatigue crack, that is, the primary crystal size of aluminum.

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Shot peening is one of the most effective treatments for improving the fatigue strength of transmission gears. As is well known, the improvement of fatigue strength is caused by the compressive residual stress. Fatigue crack propagation in the residual stress field was analyzed by the fracture mechanics approach, and the method for prediction of fatigue strength in terms of S-N diagrams is shown. Analytical prediction in accordance with the experimental results showed extreme delay of the crack propagation in the residual stress field, and also showed several possibilities for improving the fatigue strength by controlling the residual stress distributions.

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Fatigue strength in high humidity environment has been studied for ordinary structural steels such as SS400 and HT800. Cracks are easily initiated in the early stage beyond the critical humidity (between 70 pct RH and 80 pct RH), because steels are subject to localized corrosion. Fatigue strength is reduced markedly and is almost the same as that in ion-exchanged water. Thus, a transition of environmental fatigue strength was found with increasing humidity for ordinary structural steels. At high room temperature (40°C), the transition moves to a lower relative humidity, because corrosion and cracks initiate more easily.

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The influences of moisture on the fatigue crack popagation (FCP) property of advanced Nylon 46 were studied, as compared with Nylon 66. FCP property was estimated perpendicular to the injection direction of both specimens controlled for the dry condition and the equilibrium moisture content under 296K and 50% R. H. . Four kinds of tested materials were glass fiber-reinforced Nylon 46 and Nylon 66 controlled for the dry and wet condition, which are referred to as PA46(Dry), PA46(Wet), PA66(Dry) and PA66(Wet). The values of ΔK at da/dN=10^-9m/cycle, ΔK (10^-9)for PA46(Dry), PA46(Wet), PA66(Dry) and PA66(Wet)were 2.8, 2.5, 2.3 and 2.2MPa√(m), respectively. So, the resistance of PA46(Wet) against FCP property was found to be superior to PA66(Dry). From fractography and measuring crack tip heating, the resistance against the FCP property in four materials was controlled by the spherulite size of the matrix, the debonding strength between matrix and fiber, and the variation in glass transition temperature.

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The propagation behavior of small fatigue cracks in smooth specimens of an aluminum alloy (2024-T6) reinforced with 20 volume percent of SiC particles was studied under load-and displacement-controlled cyclic conditions. The development of crack closure with crack extension was measured through the compliance method. An interferometric displacement gage was used to measure the opening displacement of surface cracks. When compared at the same stress amplitude, the life of reinforced material was longer than that of unreinforced material. On the other hand, when compared at the same strain amplitude, the life of reinforced material was shorter than that of unreinforced material. From the relationship between the crack propagation rate, dc/dN, and the stress intensity range, ΔK, the rate of surface cracks in reinforced materials is higher than that predicted from the relation for long cracks. When dc/dN is examined with respect to the effective stress intensity range ΔK_eff, the rate for surface cracks in both reinforced and unreinforced materials coincides with that for long cracks, except for the case of reinforced materials under displacement-controlled conditions. The relationship between the crack propagation rate and the J-integral was almost identical for all cases examined in the present study.

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Pressure vessels are periodically subjected to a proof test to assure structural integrity. During that period, it may be possible to control the fatigue crack growth by simultaneous heating globally or locally around a crack tip. From this viewpoint, retardation behavior of a fatigue crack due to a single peak overload at a high temperature (∼300°C) was examined in an A 533 B-1 steel. Parameters investigated were overload ratio, applied temperature, hold time at higher temperature, and unloading temperature of overload. The higher the applied temperature, the greater the effect of retardation especially when unloading of the overload is done at lower temperatures. Also, the hold time at maximum load promotes oxide-film-induced crack closure. To evaluate those effects, a simple model is proposed based on the Dugdale model.

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Fatigue strength and fatigue crack propagation (FCP) of titanium aluminide TiAl have been studied at ambient temperature for two microstructural conditions ; an as-cast material consisting predominantly of lamellar (α₂+γ) grains and a heat-treated material (homogenized) composed of equiaxed γ grains and lamellar grains. It was found that fatigue strength of as-cast material was superior to that of heat-treated material. Since fatigue cracks were initiated at more than 90% of fatigue life, the observed difference in fatigue strength was attributed to crack initiation resistance of both microstructures. The FCP rates were faster in heat-treated material than in as-cast material, and when the FCP data were plotted in terms of the effective stress intensity factor range, the heat-treated material still exhibited faster FCP rates. The SEM observation revealed predominantly transgranular cleavage of γ regions in the heat-treated material, thus leading to lower FCP resistance.

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This paper presents the fatigue crack growth in Mode I of rubber toughened epoxy adhesives The effects of rubber content and adhesive thickness on fatigue crack growth were examined. The experimental results show that some of these parameters apparently do affect fatigue crack growth. The conclusions are summarized as follows : (1) For unmodified epoxy adhesives, the da/dN-ΔG_I diagram in Mode I varies according to adhesive thickness. For rubber modified epoxy adhesives, the effect of adhesive thickness on the da/dN-ΔG_I diagram is no more significant than that for unmodified epoxy adhesives. (2) Resistance to fatigue crack growth is increased by rubber modification. (3) From the fracture surface observation using SEM, it shows that the fracture surfaces of rubber modified adhesives are more complex than those of unmodified adhesives.

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This paper describes the stress intensity factor for a semicircular surface crack embedded in a finite plate of cubic single crystals of Cu, Ni, Si, Al, and W, in consideration of anisotropy caused by the crystallographic texture. The correction factor F_I of the stress intensity factor was calculated by means of the 3D finite-element method (FEM). The F_I value depends on both the material and crystal direction. The relationships among the F_I value and Young's modulus, shear modulus, and Poisson's ratio were discussed. A simple method of estimating the F_I value for cubic single crystals was proposed by introducing a parameter which expresses the intensity of elastic anisotropy. The F_I value can be estimated by this method in the range of elastic anisotropy between 1.00 and 3.20 for several crystal directions.

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For cracks with a center-hole notch under the mixed-mode condition, a method is proposed in which the stress intensity factor can be directly evaluated from the discontinuous crack displacement, thus representing effective stress intensity factors. Using this method, the effect of crack surface roughness on the stress intensity factors K_I (mode I) and K_II (mode II) was discussed especially in relation to the crack surface contact of the slant-annealed crack under tensile loading, where crack opening (or closing) was estimated to be induced gradually during loading (or unloading). Also, it was found that the residual plastic layer in the wake of the fatigue propagation crack reduced the stress intensity factors K_I and K_II determined from the discontinuous displacement along the slant crack with a center-hole notch under tensile loading.

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In this paper, a singular integral equation method is applied to calculate the distribution of stress intensity factor along the crack front of a 3-D semi-elliptical surface crack. The stress field induced by the body force doublet in a semi-infinite body is used as the fundamental solution. Then, the problem is formulated as an integral equation with a singularity of the form of γ^-3. In the numerical calculation, the unknown-function of the density of body force doublet is approximated by the product of fundamental density function and a polynomial. The smooth distributions of stress intensity factors for various aspect ratios of the surface crack are obtained by the present method. The calculation shows that the present method gives rapidly converging numerical results. The boundary condition is sufficiently satisfied throughout the crack boundary.

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Crack propagation behavior in 2-dimensional polycrystals is simulated by varying the ratio of fracture toughness between grain and grain boundary. Crack path is determined by the competition between intergranular and transgranular fracture at the tip. Regular hexagonal grains are used to construct the microstructure of ideal polycrystals, while the real microstructure is obtained from the thermally etched surface of alumina. The apparent fracture toughness at each step of crack propagation is calculated from the fracture toughness of the path plane and the stress intensity factors at the deflected crack tip obtained by the body force method. The apparent fracture toughness of the polycrystal is directly proportional to the grain boundary toughness, and is independent of the length of crack extension. For the alumina polycrystal, the simulated crack path shows good agreement with the real path when the fracture toughness of the grain boundary is 0.5∼0.6 times that of the grain. Although the absolute evaluation of fracture toughness by the simulation is not available for actual polycrystals, the phenomenological crack propagation behavior can be simulated, and its results show good agreement with the analytical results.

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Molecular dynamics simulation is performed on α-iron having two kinds of lattice orientations including the primary slip direction of [111] for bcc crystal. The crack on the (100) plane with crack tip direction [011] and that on the (011) plane with crack tip direction [011] are studied. For the crack on the (100) plane with its tip direction [011], no dislocation emission is observed, and the crack propagates on the (100) plane in both low-and high-temperature environments. For the crack on the (011) plane with its tip direction [011], brittle fracture without dislocation emission occurs at low temperature, but at high temperature [111] dislocation emission from crack tip is observed. The local stress on the cleavage plane and the slip plane is discussed from the viewpoint of fracture mechanism.

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It is well known that the interfacial property is an important factor for the strength of fiber-reinforced composites. The temperature dependence of the interfacial property and fracture mechanisms of a single fiber composite are examined by acoustic emission. Two kinds of materials, thermosetting and thermoplastic resins, are used. The fracture surfaces are observed with a polarized microscope. The interfacial shear strength of the fiber/matrix is calculated using AE events which are almost equal to the number of fiber breakages. As a result, it is confirmed that the fracture mechanisms of SFC are different when the temperature is varied. The debonding length increases and the interfacial shear strength decreases with increasing temperature for all specimens. However, it is found that the thermoplastic resin becomes extremely brittle with decreasing temperature and the fiber breakages contribute to the fracture of the composite directly.

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Analysis of fracture mechanics of the compression after impact (CAI) test for carbon fiber reinforced plastics (CFRPs) has been carried out in order to clarify the factors controlling the fracture process in the test and to establish a simpler small-scale test method. A series of methods of analysis is proposed which enables prediction of the size of the impact-induced damage and the inplane compression strength of the damaged plate based on basic properties such as the elastic modulus and the mode I and II interlaminar fracture toughness of the CFRP. The method has been applied to the standard-size and small-scale CAI tests, and it was found that the results of both tests can be predicted by the method. It was also shown that the CAI strength obtained from the standard-size test can be predicted from the small-scale test results.

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Delamination fracture toughness and fracture mechanism in carbon fiber reinforced Nylon laminates have been investigated. The mode I interlaminar fracture toughness tests are carried out on double cantilever beam (DCB) specimens made from four kinds of angle-ply laminates. These laminates exhibit the unstable "stick-slip" behavior on the crack propagation. In order to obtain the continuous G_I-R curve describing the stick-slip behavior, one modification is made to Kageyama's modified compliance method. From the continuous G_I-R curves, it is found that the stable delamination is characterized by a flat region of G_Istable &ap; 1200 J/m² for all lay-ups except for a 60°//-60°specimen which shows the rising G_I-R curve to final failure. The interlaminar fracture toughness of these composite laminates is considerably higher than that of carbon/epoxy laminates. Based on the continuous G_I-R curves and the observation of the fracture surfaces, a mechanism is proposed in which the unstable stick-slip behavior is explained by the development of the large-scale bridging of the fiber bundle or layer and its breakage.

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The failure assessment diagram was constructed to assess the structural integrity of high-pressure autofrettaged vessels with a semi-elliptical axial defect, and a systematic sensitivity analysis of factors influencing unstable fracture under the residual stress field was performed. Under the maximum service pressure, increase in the autofrettage radius has a beneficial effect on critical flaw size ac, although it has little effect on the yielding scale at unstable fracture. Increase in the fracture toughness has a beneficial effect on both factors. When the inner-to-outer radius ratio is constant, increase in the vessel dimensions has a similar effect as decreasing the fracture toughness. When the inner radius and the safety factor of the pressure concerning plastic collapse failure are constant, the relative size of ac and the yielding scale at unstable fracture decrease with increasing wall thickness. In every case analyzed, the concept of leak before break (LBB) does not hold. However, the structural integrity is assured because the critical defect size is large enough to be easily detected during in service inspection.

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Up to now, various TTP (time-temperature parameter) methods have been proposed to deter. mine creep-rupture strength by extrapolation. The TTP methods based on regression analysis, however, reflect such a general tendency of the regression curve that the estimation accuracy of rupture time is low at the lowest and highest stresses in the test stress range. For the purposes of improving the extrapolation accuracy and formulating the master rupture curve, the we authors have developed two estimation procedures employing nonlinear programming : one is an extrapolation prediction method for the creep-rupture curve under constant temperature conditions ; another is an interpolating prediction method for the master creep-rupture curve. According to the examples of extrapolation to the range of 6∼8 times as long as the test duration by the presently developed methods, these prediction methods are also applicable to cases where the deterioration of creep-rupture strength occurs under conditions of high temperature and/or long duration.

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The plane elasticity problem of a point force and a dislocation acting at a point in an anisotropic infinite plate with an elliptic inclusion was solved. Both the cases of action point of the point force and dislocation inside and outside the inclusion are considered. The solutions are also available for the case where the point force and dislocation are applied at a point on the interface.

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Link chains used in chain hoists are often subjected to combined loads of torsion and tension when the link chains are twisted by rotating burdens. Up to now, no investigations have been performed on the stress distribution of chains subjected to the combined loads. In this study, the stress distribution of chains subjected to combined loads of torsion and tension is analyzed using the elastoplastic finite-element method. Using the stress distribution in the chains, the chain strength is evaluated based on von Mises' criterion. The effects of the torsional angle of each link chain are examined using von Mises' stress. For verification, strain measurements and tensile tests were performed. A fairly good agreement is obtained between the numerical and the experimental results. It is found that the strength of link chains subjected to combined loads of torsion and tension is about 7% less than that of link chains subjected to tensile loads. In addition, it is demonstrated that chain strength can be improved by optimizing the link pitch and the link width.

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We derive Green's functions for axisymmetric body force problems of dissimilar elastic solids. Green's functions are defined as a solution to the problem of a dissimilar elastic solid subjected to axisymmetric body forces acting along a circle. In a previous paper, Green's functions were shown for the case where the body forces were acting in the region z >0. In this paper, Green's functions are shown for the body forces acting in the region z <0, where z=0 denotes the interface of dissimilar solids. An application of Green's functions is shown for the problem of a dissimilar elastic solid with a spherical cavity at the interface, by using the body force method.

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When dissimilar materials are joined at elevated temperature, residual stress is generated around the bonding interface area. Because of the stress concentration at the interface, the strength of the joint is not as great as expected. Many attempts have been made to reduce the residual stress value and to change the residual stress distribution. Many investigations using the finite-element method (FEM) have been carried out to estimate the effects of residual stress on the joining process under a homogeneous thermal field. In this works, the thermal residual stress and the strain were analyzed with FEM under thermal elastic conditions. Namely, numerical analysis was carried out for an electrical conductive ceramic of TiB₂-Ni joint under an axisymmetric condition. It was found that the principal residual stress at the edge of the bonding interface was affected by the difference in elevated temperature between the inner and outer sections of the joining materials.

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A bilinear 4-node element, widely used in finite-element numerical analysis, yields poor solutions in some cases of large elastoplastic deformation. The locking phenomenon and hourglass modes are observed when applying the exact and reduced integration techniques, respectively, for the displacement-based method. Even though the mixed method can overcome these shortcomings, the cpu time increases rapidly for a large-scale problem, because the pressure field is added to the matrix formulation and the exact integration technique becomes indispensable. On the other hand, several improved methods, such as the selective reduced integration technique, the so-called B approach and the hourglass stiffness stabilization method, have been proposed to overcome these difficulties. We here give the finite-element formulation of rate types in large deformation fields for these improvement techniques for a bilinear 4-node element and discuss the differences among these methods using the numerical simulations.

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Powder packing behavior is analyzed by the method based on the equilibrium equation of contact forces between particles. Contact forces employed in the calculation are repulsive force and friction force. Repulsive force is estimated by the rigid-plastic FEM. Two-dimensional calculations by 600 particle-modeling are carried out to observe distribution of contact forces. It is shown that friction force causes uneven force distribution in the case of uniaxial compression. On the other hand, in the case of isostatic compression, force distribution is almost even for any friction coefficient.

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To simulate not only plastic deformation of a workpiece but also that of a shot in a peening process, the effect of the interaction between the shot and workpiece in the collision is included in the dynamic rigid-plastic finite element method. In the formulation, the equilibrium equations of nodal forces are solved simultaneously with the boundary condition for velocity at the interface between the workpiece and shot. Both sliding and non-sliding contacts in the interface are dealt with, and the law of Coulomb friction is assumed for the sliding contact. Axi-symmetric plastic deformation in peening of a circular workpiece with a single shot is computed. The calculated shapes of the workpiece and the shot are compared with the experimental ones for the workpiece and a shot made from plasticine whose flow stress is controlled by temperature. It is shown that almost no plastic deformation of the shot occurs under actual shot-peening conditions for steel workpieces when the flow stress ratio of the shot to the workpiece is larger than two.

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The existence of critical impact velocity has been confirmed in experiments in which a sheet was perforated by a flying projectile. The experiments were performed to measure the values of parameters relevant to the normal impact of the cylinder against the sheets. By examining the relationship between the diameter of blanks and impact velocity, the phenomenon of the critical impact velocity was confirmed. The theoretical approach was also presented, for the same conditions as in the case of simple wave propagation, as in the Karman-Duwez solution. The comparison between theoretical examination and experimental results was also discussed.

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This paper is concerned with the exact solution of a layered half-space subjected to a concentrated force which may act either vertically or horizontally in the interior of the layer. The problem is formulated by Muki's method using Hankel transforms. We perform the inverse integrals involved analytically, and thus obtain a closed-form solution, which is represented by the associated Legendre function of the first kind. Some considerations are given for stress singularities when the concentrated force is located at the interface.

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This paper presents a polychromatic X-ray method for nondestructive evaluation of residual stress distributed in the vicinity of the interface between a ceramic coating layer and a substrate metal. Since the strain is assumed to be a linear function of the depth, the strain distribution along the depth direction can be obtained from the weighted mean strain equation calculated by considering the intensity of diffracted X-rays over the penetration depth. Therefore, the distribution along the depth direction of the residual stress was determined by the strain distributions in two directions : the vertical direction and the inclined direction to the surface. SUS316 coated with TiN by the PVD process was used as the specimen. The residual stress distributions in the coating layer and the substrate of the specimen were evaluated using this method. As a result, not only compressive residual stress in the coating layer but also the stress gradient in the substrate could be confirmed simultaneously and nondestructively.

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It has been found that the boundary integral equations for the field functions such as those of potential and displacement can be regularized by introduction of their relative quantities. This report shows that the same techniques are also applied to regularize the integral equations for the unsteady heat conduction problems. Integral equations with relative quantity of potential and its derivatives are obtained by superposing a particular solution under the condition of time-independent uniform potential on the conventional integral equations. These new equations give accurate numerical results over the entire domain. In addition, since the integral equations for the boundary and the interior become continuous, this approach has succeeded in deriving the integral equation for a boundary temperature gradient which is absent hitherto in the conventional equations. Using two-and three-dimensional examples, the present integral equations are verified to be valid and useful.

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A new method for automatically extracting relatively important zero points among singular points using a computer-assisted photoelastic technique is described. To extract the zero points, the images with the principal-stress directions in the whole field are used, which are automatically obtained on the basis of the "time-series photoelastic data" obtained from rotation of the crossed polaroids. The extraction of zero points involves analysis of the distribution of principal-stress directions around a zero point which differs from that around a regular point. To extract the locations of zero points, a window is moved on an image with the principal-stress directions, and the distribution around the center of the window is compared with a standard distribution around at a zero point. This method is applied to an angular plate under a compressive load. As a result, the accuracy of the extraction is up to 2-3 pixels.

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Groove formation at grain boundaries in crystalline aluminum is simulated by computer molecular dynamics. A bicrystal model with a [001] (310) Σ=5 tilt grain boundary and a polycrystal model are used for simulations. The simulations show that a groove forms at the intersection of the grain boundary and surface even without tensile stress. The simulation results also show that the grain boundary groove is more likely to form when the temperature or tensile stress increases, or when grain boundary annihilation occurs. We found that the likelihood of the groove formation mainly depends on the ratio of the grain boundary diffusion at the intersection to surface diffusion. When this ratio increases, the groove is more likely to form. This tendency is confirmed by investigating the effect of temperature distribution on the groove formation.

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Elaboration of the preceding one-dimensional analysis of ductile spall damage based on damage mechanics was discussed by performing axisymmetric two-dimensional analyses. The effects of surface energy due to cavity nucleation and elastic-viscoplastic-damage coupling were incorporated into the energy conservation law. Then, the application of the commercial finite-difference program MANJUSRI-3D for nonlinear dynamic analysis to the axisymmetric two-dimensional problem was discussed. Finally, a plate impact of OFHC copper discs was analyzed by the present method, and the effects of the radial stress wave and surface nucleation energy on the spall damage process were elucidated. The results of analysis were compared with those of one-dimensional analysis and experiments.

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The orthogonal nanoscale machining of copper with a diamond-like tool has been simulated using molecular dynamics, focussing on tribological phenomena such as friction at the tool-workpiece interface and tool wear. Supposing that the atomistic friction at the interface depends on the cohesion energy of the Morse potential, the level of the energy is reflected in the shape of the chip, the cutting forces and the integrity of machined surface, to a great extent. The tool wear has been simulated by reducing the cohesion energy of the tool atoms. The wear mechanism involves interdiffusion of the workpiece and tool atoms, and re-adhesion of the worn particles to the tool. The shape of interface potential and the tool wear distributions also affect the minimum thickness of cut and the depth of the region where the displaced workpiece atoms exist : two and ten atomic layers are their minimums, respectively. The influence of the friction and the tool wear on the cutting mechanism in nanoscale machining is similar to that observed in macroscale machining.

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When a bar falling or moving at any speed strikes the opposite side of threaded rod fastening a thick circular disk, stress wave propagating from the collision interface is transmitted into the assembly system, tightening the thick circular disk by the bolt-nut unit. This paper experimentally studies the relationship between the loosening response of bolt-nut fastening assembly system and stress wave modes (tension or compression) along the direction of propagation. The technique of observing the loosening of a bolt-nut assembly system by monitoring the configuration of stress waves reflected from the surface of a thick circular disk is presented. The axial stress of a bolt tightened by a hexagonal nut in conjunction with a plain washer, a spring washer or a flanged nut is measured, when a number of incident waves are impinged into the assembly system. The shift of axial stress due to tightening by flanged nut is the smallest.

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When a transversely isotropic solid cylinder is subjected suddenly to a uniform temperature rise, a stress wave occurs at the surface the moment thermal impact is applied. The stress wave at the surface proceeds radially inward to the center of the cylinder. The wave may accumulate at the center and give rise to very large stress magnitudes, even though the initial thermal stress is relatively small. This phenomenon is called the stress-focusing effect. In this paper we precisely analyze the effects of these waves using the ray series. The results give clear indications of the mechanism of the stress-focusing effect in a transversely isotropic solid cylinder.

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In this paper, a genetic algorithm for continuous search space is proposed and its use for nonlinear inverse problems is further described. The algorithm uses a population of individuals each represented by a real vector. The performance tests of the algorithm were conducted for the optimisation of some different functions with continuous variables, and the results of the tests were compared to the performance of the canonical GAs. The results show that the algorithms optimise the functions more efficiently than the canonical GAs in terms of the time and memory required for computation and the convergence rate. The algorithm was then applied to the parameter identification of a thermal conductivity problem. As a result, the algorithm was able to find a parameter set close to the exact solution even when the measured data were subject to noise.

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This paper describes a cellular automaton generating an adapted structure for an arbitrary loading condition. The mathematical model is based on the remodeling (functional adaptation) of living systems. The model consists of identical cells which mechanically connect with each other. Each cell changes its Young's modulus, sensing the mechanical condition around the cell. We examined the performance of the model, giving each cell local rules with a nonlinear relationship for the change in Young's modulus. The local rules are "death", "birth", and "split" as in living systems. The computer simulation showed that the model formed a clear framed structure satisfying the boundary condition.

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Three-dimensional fiber reinforced composite materials produced by impregnating resin in woven fabric have superior interlaminar and impact strength, and are capable of being formed into complex shapes. They are also tailored materials, so we can obtain the required material properties by designing the 3-D fiber construction appropriately. In this report, we propose an optimum design method for 3-D composite materials. The weight and cost minimization problems constrained by failure stress and failure loads are considered. The strength analyses are performed using the stress averaging method which gives efficient calculation, and the genetic algorithm is applied in the optimization. The calculation is executed for the 5-axis woven CFRP 3-D composite, and the validity of the present design method is discussed.

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In order to consider the tribological properties of magnet-structural materials at cryogenic temperatures, the authors require the hardness value of the materials at cryogenic temperatures. Therefore, a low-temperature Vickers-type hardness tester has been developed. The hardness tester consists of the driving device of the indenter, load control system, specimen transfer device and cooling system. The measured hardiness for eight materials were equivalent to those obtained by a conventional Vickers micro-hardness tester at room temperature which means that the developed hardness tester has sufficient performance as hardness tester. The temperature dependence of the hardness was obtained between 77 K and 293 K for stainless steels of JN1, JN2 and SUS316L, Ti-alloy and Copper. It was found that the hardness increased with decreasing temperature, where the hardness at 77 K is three times the hardness at 293 K for stainless steels, and is twice for copper. The relationships between the increase of hardness and the reciprocal of temperature were expressed in Arrhenius equations. The relationships between hardness and yield stress or tensile strength were examined. The hardness is more than three times greater than yield stress or tensile strength.

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To understand the ink flow mechanism in mimeographing, the mechanics of fluid-saturated poroelastic solids is applied to analyze the elastic deformation of and the ink flow through a screen/printing-master layer which is pressed from below by a press roller and subjected from above to hydrodynamic lubrication pressure induced between a printing drum and an ink roller by rotation. The deformation and the accompanying ink flow are shown to be governed by four nondimensional parameters newly defined here. The numerical results show some important results ; e.g., squeezing out of the ink from the layer due to the layer compaction by the press roller plays an important role among various possible ink flow mechanisms, especially for the case where the compression duration is slightly smaller than the characteristic time of the layer.

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A mathematical model for pulmonary circulation is established taking into account the mechanical behavior coupled with breathing dynamics. The blood flow models in the arterial and venous trees are established by assembling the tube-flow model in each elastic vessel. These models are combined with the sheet-flow model which expresses the blood flow in the capillary network. The finite-element discretization based on adjoint variational principle is applied to solve the model numerically. First, the pulmonary blood flow under a constant gas pressure in the lung is measured using rabbit lungs, and the decrease in blood flow due to gas pressure is observed. The simulation model is verified by comparing the experimental observations with the simulated results, and the causality among the decrease in blood flow, the capillary collapsing and the pressure distribution is discussed. Next, the pulmonary circulation model is coupled with the breathing model to examine the input impedance in normal breathing and to evaluate the effect of varying the inhaled gas pressure in artificial ventilation. It is shown that the results obtained in the simulation correspond to the impedance characteristics observed in experiments in different species. The simulation of artificial ventilation demonstrates that the inhaled gas pressure affects the blood flow not only in arteries and veins but also in the capillaries. These results indicate that the simulation based on the proposed model can be used to investigate the internal mechanical behavior of the pulmonary circulation taking into account the variation due to individuality of the geometry and material properties.

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