A stress analysis of a human lumbar motion segment (L3-L4) containing two adjacent vertebrae and the intervertebral disc under compression was carried out using the finite element method. In the plane model traced precisely from an X-ray photograph, the five substructures were incorporated: each of the vertebral bodies, the annulus fibrosus, the nucleus pulposus, the anterior and the posterior ligaments. As a result, for a lumbar segment with a healthy disc, the region of highest stresses in the cortical bone was found at the center of the vertebral end plate in contact with the nucleus pulposus and at the posterior wall of the lower vertebral body. In addition, below the nucleus pulposus to the posterior wall of the lower vertebral body, the weakest region was observed in the cancellous bone. Therefore, the mechanism of burst fracture at a lumbar spine was estimated from this analysis.

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A constitutive model for blood vessels is formulated with special emphasis on smooth muscle activation. The activation of smooth muscle gives rise to the contraction of blood vessels and changes in their mechanical properties. Thus, we first characterize the state of activation by employing the stretch ratio between the stress-free configurations in the active and the passive conditions and by representing the material constants of the pseudo-strain energy function in terms of the measure of activation. The pseudo-strain energy function was expressed in the form of the polynomial of the second strain invariant. The proposed constitutive model was employed to simulate some previous data of canine arteries in different sites or in different degrees of activation. It was observed that the present model can describe the mechanical behavior of blood vessels with various types of deformation properties in activated states and of those in a wide range of activated conditions.

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A general formulation for the reliability model of unidirectionally fiber reinforced laminate is developed. One of the major objectives of the present paper is to show a practical method of constructing the reliability-oriented materials design. The proposed formulation is developed based on six kinds of failure criteria which borrow features of the Mises's isotropic yield condition, Hill's orthotropic yield condition, maximum stress and strain criteria. For the evaluation of reliability of unidirectional fiber reinforced laminate, a reliability evaluation model was constructed by the First/Second Order Reliability Method(FORM/SORH). Numerical examples for graphite/epoxy laminate are shown for the comparative verification of failure criteria under the various co9bination of multiaxis load condition and lamination angles.

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The impact fatigue test was carried out on an epoxy resin filled with Si0₂ particles. The effect of the Si0₂ content ratio on the impact fatigue strength and the effect of the impact repeating speed and the life to failure on fracture surface morphology were examined. The impact fatigue strengthσ_t can be estimated by the formula of σ_t (N_fT_e)^mt =D_t, where N_fT_e. is the cumulative duration time, and mt and D_t are parameters of the impact fatigue properties. The impact fatigue strength and static strength were governed by the content ratio of the Si02 particles. The crack initiated by decohesion at the epoxy-Si0₂ interface and the stable crack grew along this interface under the monotonic and the impact repeated loading conditions. During the unstable fracture, however, the crack propagated regardless of the existence of the Si0₂ particles.

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The plane elastostatic problem of a crack branching at a fiber/matrix interface in carbon fiber reinforced composites is considered using a micromechanical model. The model is a crack which originates in one half plane and branches at a bimaterial interface of a bonded plane consisting of an isotropic and an orthotropic half plane. The method of continuous distribution of dislocations reduces the problem to a system of simultaneous singular integral equations of the second kind, which is solved numerically by use of the Lobatto-Jacobi integration rule. The singular stress field at the crack tips is investigated in terms of stress intensity factors and crack opening displacements.

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The mechanical properties of thin-plate and thin-pipe specimens of Type 316L austenitic stain-less steel (thickness t : 0.05 to 1.0 mm, grain size d : 65 to 353 μm) were investigated at room and elevated temperatures. The tests were carried out with tensile tests at room temperature, 573K and 923K, and with creep tests at 923K only. The ultimate tensile strength σ_B and the total elongation et generally decreased with a decreasing value of t/d when the ratio was smaller than the critical value. The critical value of t/d was estimated as 8 to 10 forσ_B and ε_t at room and elevated temperatures in this study. The fracture mode of the specimens was generally ductile fracture with severe local contraction at the smaller value of t/d and at the elevated temperature. The creep rupture time T_r decreased with increasing d and an initial creep stressσ_C, and the steady-state creep rate δ_S increased with increasing d and σ_C of thin-plate specimens. These dependences of T_r and σ_C on d andσ_C were similar to those of bulk specimens, but the value of o. of the thin specimens was very low in comparison with that of the bulk ones because of the weakness when the value of t/d was smaller than critical value.

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Effects of primary sintering and carburizing treatments on the fatigue strength of a Fe-C-Cu-Ni sintered gear were investigated. It was found that carburizing was the most effective treatment for the improvement of fatigue strength of the sintered gear. The notch effect on the fatigue strength was also investigated by means of a sintered specimen with various stress concentration factors, α_e. The fatigue strength of notched specimen was generally insensitive toα_e. Based on the results thus obtained, the prediction method of fatigue strength of the sintered gear was discussed by applying FEM analysis. The predicted fatigue strength comparatively agreed with the experimental result.

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The acoustic emission (AE) method is one of the most noticeable methods of late used to detect the dynamic behaviour of the microstructure in materials. In this paper, the tensile test of an aged Al-Li-Cu-Mg-Zr alloy was carried out to clarify the relation between the detected AE activities and the dynamic behaviour of the microstructures including dislocations, precipitates and secondary phases. The AE activities had the maximum value in the underaged condition near the yield point of the stres-sstrain curves. Afterward, the AE activities decreased progessively with aging. The AE did not occur in the post-and overaged conditions. Both the continuous type and the burst type signals which depend upon the avalanche of the dislocation motion and the shear of precipitates, respectively, have been detected at the same time. By the transmission electron microscopy, superlattice dislocations, metastable δ' phases and the increase of dislocation density were observed in the underaged condition where the AE activities showed a peak. According to these results, it was estimated that the AE sources of this alloy during tensile deformation were the shear of metastable ' phases and the avalanche of dislocation motion.

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Cavitation erosion of carbon steels coated with TiC and TiN using CVD was studied in distilled water and 3% NaCl solution by using a magnetostrictive facility. When cavitation attack occurs to coatings, the process of erosion is as follows: soft ferrite grains under the coatings are first deformed by alternative collapse pressures. The coatings are then fractured by initiating and propagating of cracks from those between coatings and substrate. Finally, the substrate is remarkably eroded in only small parts where coatings are fractured. Therefore, the thickness of coatings and the hardness of substrate are significant parameters for the increase of erosion resistance.

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High-cycle fatigue, fatigue crack growth and fretting fatigue tests were carried out using sintered high speed steel SKH10 as well as the melted steel. The high-cycle fatigue and fretting fatigue strengths in sintered SKH10 steel were higher than those in the melted one by a factor of 1.2-1.3. However, the crack growth rate of sintered SKH10 steel was higher than that of the melted one. The higher fatigue strength of sintered SKH10 steel seemed to result from the fine and uniformly distributed carbide precipitates in the martensitic matrix, while the melted one had coarsen carbides which were the nuclei of fatigue crack. The higher fretting fatigue strength of sintered SKH10 steel was mainly caused by the low frictional coefficient between the contact pad and the specimen. The prediction of fretting fatigue life was made on the basis of the fracture mechanics analysis proposed in the previous paper, where the frictional force was taken into consideration. The predicted lives were in good agreement with the experimental results.

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As a short-fiber reinforced PET composite has excellent properties such as low cost, light weight and high strength, the composite has been used in many fields of industries. When the composite is used for machine elements parts, reliability and safety are needed. In this paper, the relationship between the fracture behavior and the acoustic emission characteristics is investigated by static tensile and tensile fatigue tests and by fractographs. It is found that the AE event count rate is a useful parameter to represent the pattern of macroscopic fatigue crack growth behavior and the AE frequency spectrum clearly corresponds to the microscopic fatigue fracture behavior of constituent elements.

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Rotary-bending and push-pull fatigue tests were performed for JIS S15CK low-carbon and SNCM439 alloy steels. The fatigue lives for crack initiation and final failure plotted against stress amplitude were much shorter in push-pull loading than rotary-bending loading. This difference in fatigue lives almost disappeared however, in the life curves plotted against the cyclic strain amplitude, which was measured during fatigue tests. The surface crack growth rate, da/dN plotted against the strain intensity factor range, and ΔKε were expressed by a linear line on double logarithmic scales, independent of the test mode. The fatigue life for crack propagation was esimated by integrating the equation derived from this da/dN vs.ΔKεrelation. The life estimated in this way produced only a small difference between the rotary-bending and the push-pull fatigues, compared with the the scatter found in the presest data. Thus, the strain-based fatigue life is hardly influenced by the test mode in the crack propagation and crack initiation processes.

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Safety evaluation of components with crack-like defects must be treated probabilistically because the initial size of defects and other parameters are nondeterministic. In the case of an actual structure, such as a pressure vessel, the most important defect is the surface flaw. But life prediction involving surface flaws is not simple, as the aspect ratio of a crack may change gradually as the crack grows. Therefore, probabilistic analysis is also complicated. This paper presents a simple method of probabilistic life prediction for the fatigue crack propagation of a semiellipitical surface crack, and the influence of several parameters on crack propagation life is discussed.

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Several tensile stress-strain curves on virgin material corrected after maximum load have been studied, but few on compressive prestrained material have. We made tensile tests on copper round bars with maximum 80 % of prestrain. The main results obtained are as follows : (1) Tensile stress-strain curves corrected by dimensions of necking have a tendency to be equal in a large strain zone. (2) There is a point where the change of R/ρ with progress of deformation slows down and in this point, the value of ρ/R₀ is approximately 2 (ρ: longitudinal radius of necking, R : the minimum sectional radius, R₀ : initial radius of section) . (3) Only in the case of over 25 % prestrain are characteristic phenomena seen when compared with the case of virgin material.

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The shock response of a bar supported elastically at one end, another end of which is subjected to an impact compression, is analyzed numerically by the Boundary Element Retarded Potential Method (BEM) . The measured values of the stress or the displacement history on the ends of the bar were used as the input data of the mechanical or the geometrical boundary conditions for BEM analysis. The results obtained by using four sets of the boundary conditions were compared with the experimental results. The results calculated from the mechanical boundary conditions only were in good agreement with the experimental results, while excessive noise appeared easily in those done with the geometrical boundary conditions. The filter treatment of the noise in the measured displacement data made the successful calculation possible.

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When a solid sphere is subjected suddenly to a uniform temperature rise over its cross section, 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 sphere. 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. This paper analyzes the effects of these waves precisely using the ray theory. The numerical results give clear indications of a stress-focusing effect in spheres

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Various quench cracks of steel are considered in general to occur under the united thermal and transformational stresses. This paper deals with the effects of characteristics of ethylene glycol (EG)-water quenchant on quench cracks (fin and/or vertical). Cooling rates of silver and steel bars in EG solution (up to 80 vol%) become lower as the concentration of EG increases, while at over 80 vol%, the rates bring the reverse change. This behavior of cooling rates is due to the unique specificity of boiling points in the EG water system. The fin crack by EG solutions ranging in concentration to 80vol% occurred in all specimens at the austenitizing temperatures higher than 780'C. A quenchant containing more than 90 vol% EG results in the decrease of a fin crack and an increase of the vertical crack. Residual tensile stress existed on the surface of the test piece and increased with austenitizing temperature.

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The bonding of ceramics and metals is an effective method for applying ceramics to structural materials. The previous paper noted that high stress concentrations are induced only at the narrow region near the outer surface of ceramics, and that the stress concentration can be reduced by modifying the shape of the ceramics. In the present paper, the effect of the modification of the ceramics geometry on the stress concentration in the thermoelastic-plastic analysis is compared with that in the thermoelastic one. The values of the stress concentration in the axial direction have a tendency to increase with reducing the elastic modulus for the metals. The relationship between the ceramics geometry and the stress concentration in the thermoelastic-plastic analysis can be qualitatively estimated from that in the thermoelastic model by changing the elastic constant into the work hardening modulus for the metals.

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This paper deals with the cyclic plastic problem of a strip with a hole subjected to cyclic loading at the ends. For the numerical analysis, the constitutive model, in which the motion of the center of the yield surface is incorporated, is implemented in a finite element method. The distribution of strain and stress, and the development of the subsequent yield surface during cyclic loading are discussed in detail both for the zero and nonzero mean value of cyclic load. To verify the results of the computer simulations, the experiment of a strip with a hole of type 304 stainless steel is carried out. As a result, even the cyclic loading with nonzero mean value of cyclic load, strain at the bottom of the circular hole is ratchetted with increase of cycle, and stress and the subsequent yield surface approach to those due to the zero mean value of cyclic load.

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As one of the analytical models of the thermal stress problem for composite materials, we consider a hollow circular cylinder composed of multilayered composite laminate and discuss the transient thermal stress problems of a hollow cylinder with a uniform heat supply from the outer or inner surface. In studying the analytical developments for a multilayered composite cylinder, we introduce the method of Laplace transform for the temperature field and Airy's stress function method for the thermoelastic field. and then evaluate the temperature and thermal stress distributions in a transient state. Extending the theoretical developments proposed in the present paper to the analysis of a hollow cylinder with nonhomogeneous material properties, we examine the thermal stress distributions and the effect of relaxation of stresss values in nonhomogeneous cylinders made of functionally gradient material.

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The theoretical treatment of thermal bending and thermal stress problems involving a multilayered anisotropic laminated slab in a transient state is discussed in this paper. As an analytical model, we consider an infinitely long laminated slab consisting of an orthogonal pile of layers having orthotropic material properties, i. e. a cross-ply laminate. We solve the thermoelastic problem for a case where there is a uniformly distributed heat supply from the upper and lower surfaces of the slab. Introducing a method of Laplace transform for the temperature field, we obtain the temperature solution with the aid of the residue theorem and evaluate the characteristic behavior of thermal bending and thermal stresses in a transient state using the elementary plate theory. As an example, we carry out numerical calculations for a 5-1ayered cross-ply laminate and closely examine the numerical results.

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The numerical analysis of the elasto/visco-plastic dynamic response of axisymmetrical thin shells subjected to arbitrary loads is carried out by the elasto/visco-plastic overlay model which is able to express the Bauschinger effect and the strain rate dependence. Namely, Perzyna's equation is used for the constitutive relation of each layer of the overlay model, and as a whole, the Bauschinger effect and the influence of viscosity in plastic range of the material are taken into account. The equations of motion and the relations between the strains and displacements are derived by extending the Sanders linear theory in elastic shells. The numerical method selected for this problem is a method using finite difference in both space and time. In order to check the adequacy of the numerical analysis, experiments are performed on the elasto/visco-plastic response of an aluminum cylindrical shell subjectd to locally distributed impulsive loads. On the whole, relatively good agreement is obtained between the experimental results and analytical solutions.

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The three-dimensional elastic problems in finite deformations are not known to have been analyzed by the usual stress function and displacement function. By applying Hasegawa's presentation and Adkins perturbation method, we propose a new analytical method of three-dimensional elastic problems for compressible materials and incompressible materials, respectively, using the displacement function for axisymmetrical elastic problems in finite deformations with surface force or body force. Further, this analytical method is examined by a simple example.

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A method of solution is developed for the torsion problem of a hemispherical elastic solid embedded in an elastic half space. It is assumed that the contact surface between these elastic bodies are perfectly bonded to each other, and the flat plane of the hemispherical solid is subjected to a torsional displacement by a rigid circular stamp. This problem becomes the so-called Reissner-Sagoci problem if we assume that the elastic constants for a hemispherical solid are equal to those for a half space. The principle of the method of solution presented is to distribute torsional body forces so as to satisfy the boundary conditions at the contact surface. For this purpose, we use three analytical solutions that are (1) the solution for the so-called Reissner-Sagoci problem, (2) Green's functions for torsional body force problems of an elastic half space with a fixed boundary and (3) Green's functions for torsional body force problems of an elastic half space with a stress-free boundary. Numerical results are presented to show the influences of elastic constants on the distributions of stresses and displacements.

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Better fracture resistance is given by the branched crack than non branched one. That is called the crack branching effect. In this paper, the crack branching effect is investigated analytically and experimentally. Stress intensity factor (SIF) of CT specimens with various branched crack parameters as crack length ratio, branching angle and branched crack length ratio were analyzed. The crack branching effect, the ratio of the SIF of non branched crack to the effective SIF of branched crack was approximated by the polynomial equation using parameters above. The maximum crack branchicg effect, in this study, was obtained when these parameters were minimums. The fracture tests were conducted using specimens with SCC branched cracks to determine the experimental crack branching effect, the ratio of the apparent fracture toughness of SCC specimen to the fracture toughness of the non branched fatigue cracked specimen. The experimental crack branching effects were larger than those obtained analytically. It is recognized that the discrepancy between the crack branching effects determined by the analysis and experiment was attributed to the fact that SCC was three dimensional in shape, whereas the SIF were analyzed by the two dimensional FEM and that the conservative crack branching effect is estimated by the analysis.

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The dynamic fracture toughness for a carburized steel, SCM 415, was evaluated using a computer-aided instrumented Charpy impact testing method (CAI-system) and the impact response curve method in the standard Charpy-size carburized and hardened specimen with a machine notch. The fatigue crack was set in the notch tip. The 0.2 mm precracked specimens showed a transition behavior in the relation between the dynamic fracture toughness and the temperature, whereas the 0.4 mm precracked ones did not show this phenomenon. Therefore, the hardness and carbon content in the position of the precrack tip inside the hardened case gave an important effect to the dynamic fracture toughness of the material such as carburized steel.

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A combination of the boundary element method and the finite element method is used to calculate the stress intensity factors of mixed-mode crack problems. In this method, finite elements are only allocated near a crack tip and boundary elements are used to discretize the rest of the structure. The virtual crack extension method is applied to the finite elements to obtain the stress intensity factor, together with the method for the separation of displacement components into Mode I and Mode II. The analyses are performed for a center slant crack or a center arc crack in a rectangular plate subjected to uniform tensile stress. It is found from the analyses that the present method gives an accurate stress intensity factor for mixed mode crack problems.

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The purpose of this study was to investigate the bending strength of a disc made of brittle materials. In the experiment, a plaster disc with a hole at the center was simply supported along the outer edge of the disc, and was subjected to a uniformly distributed load from a liquid pressure on one side of the disc. From the experimental data, it was found that the rupture pressure of the disc with a constant ratio of thickness to diameter was influenced not only by the diameter ratio of the hole and the disc, but also by the diameter of the disc itself. Then it was found that, while keeping the diameter ratio constant, the strength of the disc decreased as the diameter of the disc increased. We also made a theoretical analysis taking into account the effect of the "surface layer". That analysis coincided well with this experiment. From the analysis and experiment, it was concluded that there was the "size effect" in the strength of the disc.

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Mixed-mode fracture tests for sintered silicon carbide and sintered silicon nitride were carried out by torsion. The specimens with two types of indentation crack as pre-crack were prepared. The one was with a residual stress by indentation, and the other one was without it removed by grinding. These test results were compared with test results with bending formerly reported. According to the test results of the case of SiC and Si₃N₄, it was cleared that the direction of crack propagation was perpendicular to loading direction of tensile normal stress, and that the value of K_II/K_CI differed with a existence of the residual stress and a loading condition.

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The 25% side-grooved CT specimens are analyzed elastic-plastically by the 3-dimensional finite element method based on the large deformation theory. An iterative computation is carried out by the method proposed by Marcal. For ICT specimens without a side groove, the J_M value obtained from Merkle-Corten's simple equation can estimate the J value at the central part of the specimen more accurately than the J_CI value obtained from Clarke et al 's simple equation For 25% side-grooved specimens, the distribution of J_X value along the crack front becomes nearly uniform independent of the crack front configuration. The effective thickness 0.95√(Bo·Bn) (Bn=net thickness) is more appropriate than the others The J value obtained from Merkle-Corten's simple equation by using 0.95√(Bo·Bn) can estimate the J value at the central part of the specimen within about 5% error.

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The fiber bridging effect, which affects the crack extension resistance in fibrous composites, is discussed in the case of in-plane shear mode crack extensions parallel to fibers in unidirectional fiber-reinforced composites. We first consider the formation process of a bridging fiber and then make a model of this single fiber bridging to characterize precisely the behavior of a bridging fiber under the relative displacement between upper and lower crack surfaces. By using this model, the force acting on crack surfaces through a bridging fiber is estimated. Then, introducing stochastic process of fiber breakage, we obtain the quantitative relationship between the relative crack surface displacement and the equivalent cohesive stress which is the probabilistic expectation of forces acting on crack surfaces due to a large number of bridging fibers. We numerically simulate the crack extension behavior with the cohesive stress acting on crack surfaces, and find that the simulated result is in agreement with the experimental results of a unidirectional glass fiber-reinforced epoxy composite. We finally conclude that the in-plane shear mode crack extension is greatly affected by the stochastic process of fiber breakage.

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Flaws in structures often arise at the stress concentrated parts such as notch roots and welding joints, and those shapes are sometimes surface cracks. The strength evaluation of flaws is needed promptly in the facility site, since the flaws have been detected during the in service inspection. This paper describes the development of a strength evaluation system of surface cracks based upon the linear fracture mechanics using a 16 bit personal computer. The purpose of this development is to evaluate the strength of flaws at the stress concentrated parts of structures in the facility site. The stress intensity factor analysis by the influence function method and crack propagation analysis is dealt with in this system. The results are represented on the graphic display.

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A solution is presented to a three-part mixed boundary-value problem for an infinite elastic solid containing a penny-shaped crack indented by a disc-shaped rigid inclusion. The problem is reduced to a solution of infinite systems of simultaneous equations in which the normal displacement on the crack surface is expressed as appropriate series. Numerical results are given for the contact stress and the stress intensity factor at the crack tip. The effect of the inclusion on the stress field is studied.

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This is a preliminary investigation to examine the usefulness of AHP approach toward structural synthesis. It was confirmed by simple examples that it is really useful for this purpose, since not only quantitative information but also qualitative one can be taken into analysis and it permits decisions on multiple standards. Many pieces of information on manufacture are more qualitative than quantitative so that the introduction of AHP facilitates the integration of preliminary, detailed and production designs. AHP helps a designer foresee the situation and helps him make decisions in trials and errors. It is further suggested that AHP will be easily linked with the object programming approach.

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An attempt is made to constitute an integrated consultation system for structural analysis. The objective at present is to afford a prototype consultation system the ability to recognize a structure and its properties in terms of the physical model and to predict the model response qualitatively. Elastic beams and plates are taken for the physical model. The system consists of the analysis knowledge base and structure-domain base of the physical model linked mutually by message communication and supported by the inference engine. The knowledge is stated in the form of the frame model. A symbolic processor is provided for the manipulation of equations and formulae. The inference engine is described in Prolog language. The system is implemented on a personal computer PC 9801 VX 2. The case studies of beam problems assure the potential of the prototype system to evolve into sophisticated consultation systems by large computers in the future.

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Improvement techniques of the sensing system proposed in the previous paper are described. By the sensing system, optional contact pressure distributions are measured automatically. In the system, piezoelectric ceramics are used and a special electric circuit is designed to measure electric charge in the material. In the electric circuit, the FET with the integral and peak hold circuits is used to increase the measuring points and speed. A sensing system of 20×10 measuring points and a 2-second measuring time is designed. By using this system, the contact pressure distributions for several problems are measured. The obtained total force and the pressure distributions are compared with the corresponding acting forces and the theoretical values.

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An analytical method to estimate the temperature and stress distribution in an ingot due to a steady vertical semicontinuous direct chill casting process in a spatial coordinate system is presented in this paper. The interaction between temperature and phase change is carefully discussed to obtain the heat conduction equation including latent heat generation with the consideration of material flow. A viscoplastic constitutive relationship capable of describing the viscoplastic solid as well as viscous fluid is employed for stress analysis. As an example of the simulation, a casting process for axisymmetric aluminum ingot is examined by use of the finite element method, and the calculated results of temperature, deformation and stress are revealed to simulate the actual behavior during semicontinuous direct chill casting process.

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This report deals with the interaction problem of two cracks in two bonded anisotropic elastic media under longitudinal shear. One crack is placed in one semi-infinite medium and the other in another semi-infinite medium. The singular point method is adopted to solve the problem. Numerical results are shown for the influences of the geometrical parameters of the crack arrangement and physical properties of the anisotropic bodies on the stress intensity factors.

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