Fatigue crack growth tests of several ceramic materials were carried out to investigate the general characteristics of cyclic and static fatigue crack growth in ceramics. The cyclic effect was found in Si₃N₄. Al₂O₃ and TiB₂, where the main fracture mechanism was the intergranular fracture. On the other hand no cyclic effect was observed in SiC or ZrO₂, where the main fracture mechanism was the transgranular fracture. The fatigue crack growth curves were found to be reduced to a unique curve by using Δ K_eff/E, regardless of the kind of ceramics.

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Of growing importance under sever circumstances is the study on stress analysis and fracture mechanics for composite material structures. Particularly, the primary concern in design of structures and machines should be the initiation of cracks due to excessive deformation, exfoliation in material or other material defects. In evaluating safety, it is indispensable from the structural design point of view that the k value should be made known by an analysis conducted in advance. In this study, the stress intensity factor (Mode II) under a pure shear stress was obtained using the photoelastic method and caustic method, applying an isotropic material and an orthotropic material (copper fiber epoxy composite (C.F.E.C.) developed by the authors), each containing a crack, to the fracture mechanics. Results were compared with theoretical values. As a result, this method was found useful and the effect of the direction of the primary axis of this material on the stress intensity factor was clarified.

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Numerlcal simulations considering spatial and size distributions of nonmetallic inclusions in the material have been carried out for the purpose of initiating a discussion concerning the critical size of the inclusion responsible for the fatigue failure of high-strength steel. Results show that the geometrically largest inclusion within a critical volume of the specimen is not necessarily responsible for the fatigue failure of such material, and that the most dangerous inclusion for fatigue failure is that of the near surface having the largest relative inclusion size calculated from the spatial distribution of inclusions within the critical volume of the specimen.

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In previous papers, the authors discussed the J-integral range, ΔJ, evaluated by the path-integral and showed that ΔJ was a good parameter for characterizing the crack tip stress and strain fields under elastic-plastic conditions. In this study, finite-element simulations of fatigue crack growth at notches in a plate under uniaxial stress were conducted to examine the applicability of ΔJ to short fatigue cracks emanating from notches. It was found that Δl-values evaluated by the path-integral were almost path-independent when the minimum-load level or the crack-opening level was selected as a reference level for the evaluation. The value of ΔJ evaluated based on the crack-opening level correlated well with the crack-tip-opening displacement, while ΔJ based on the minimum-load level and the effective stress intensity range ΔK_eff did not. Crack closure was mainly responsible for the initial decrease in ΔJ-value and the deceleration of crack growth rates of short cracks emanating from notches.

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In order to study the statistical properties of the corrosion fatigue process, rotating bending fatigue tests of heat-treated 0.45% C steel smooth specimens were carried out in 3% NaCl solution. The emphasis is to perform the successive observations by the plastic replica method. The results show that the initiation life distribution of a crack from a corrosion pit is expressed by the two- and three-parameter Weibull distributions for high and low stress ranges, respectively. The crack length distribution is expressed by the three-parameter Weibull distribution with the exception of the distribution just before the fracture in a low stress range. Moreover, the effect of periodic plastic replications on corrosion fatigue behavior was statistically investigated.

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In this paper, the indirect boundary integral method is applied to the singular elastic stress analysis of an electric conductor with a crack in the uniform magnetic field. The simple-layer potentials and the double-layer potentials are used as the solution. The volumetric integrals, involving an electromagnetic body force, are transformed to surface integrals under uniform magnetic field and steady-state current field. As a concrete example, the ring-shaped crack in an infinite body is treated, and the stress intensity factor and the displacement on the crack surface are obtained.

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To analyze the response of FRP laminated plate under low velocity impact, the laminated plate theory is applied frequently. The stresses of laminated plate in this study are analyzed by what we call an approximated three-dimensional (3-D) theory. In this theory, in-plane stresses are obtained from higher-order plate theory and out-plane stresses are derived from 3-D equilibrium equation. The objective of this study is to confirm the applicability of approximated 3-D theory to static stresses for [0°/90°] sym CFRP plate under partial distributed load. The stress distributions along the thickness direction were compared with those of the exact 3-D theory.

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To examine the validity of three yield criteria with planar anisotropy [i.e., Hill's (1948) quadratic, Gotoh's biquadratic and Hill's (1990) nonquadratic criteria], commercial-purity aluminium and deep-drawing-quality steel sheets are tested in uniaxial tension and uniaxial (through thickness) compression. For Hill's criteria, two cases are considered here : (1) the material parameters are mainly evaluated by using γ-values, and (2) the material parameters are mainly evaluated by using yield stresses. Both the experimental γ-value and uniaxial yield stress versus orientation relationships are fairly well predicted by Gotoh's criterion. Hill's 1990 criterion for case (2) gives a more accurate fit to the experimental results of yield stress than the earlier quadratic criterion for case (1). However, the new Hill criterion for case (2) does not fit the corresponding values of γ versus orientation very well.

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The problem of a smooth circular punch penetrating an elastic half-space with a spherical cavity is considered. The solution, which accounts for the disturbances in the contact stress distribution under the punch due to the subsurface cavity, is carried out within the classical theory of elasticity. The mixed boundary-value problem is reduced first to a pair of dual integral equations, and then to an infinite system of simultaneous equations. The results are presented, illustrating the dependence of the contact stress disturbance upon the geometrical parameter of the punch.

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By using the thermo-poro-elastic theory proposed by the author previously, thermal stresses are analyzed which are induced in a fluid-saturated porous hollow cylinder subjected to a sudden rise in temperature and pressure on its inner wall. Since the problem formulated is axisymmetric, the displacement field is decoupled from the temperature and pore-pressure fields, which are still coupled with each other. Coupled diffusion equations for heat and fluid flows are solved by the Crank-Nicolson implicit method, because they involve nonlinear and integral terms. The attention is focused on the effect of heat transportation by fluid flow through pores on the temperature and thermal stress distributions. This effect is very marked for the case where fluid diffusivity is much lager than the thermal one, as suggests the possible control of thermal stresses by active fluid injection.

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The nonlinear shell finite-element (FE) model is newly developed to investigate the bending effects in large deformation and strain of plates in contact with the arbitrarily shaped rigid body. The C⁰ continuity shell model, named the modified Mindlin shell, is employed. The flat shell element is assumed to have constant in-plane strain in each layer, divided in the thickness direction. The other features of FE analyses are implicit-type updated Lagrangian formulation, Hill's normal anisotropy elastic-plastic model, Coulombic friction law, and the Newton-Raphson method to solve the nonlinear equation. The bending effect on the deformation has been demonstrated in the case of rectangular plates stretched by the hemispherical rigid punch.

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The contact torsion problem of two cylindrical rods is investigated by considering the sliding contact. When the two semi-infinite rods are contacted at each end, pressure is divided at the corner due to the stress singularity. Thus, the analysis proceeds in consideration of this stress singularity by using the series expansion method. It is considered that the shear stress is linear to the pressure in the sliding region. The relationships between the sliding region and the torque or the friction coefficient are obtained by numerical calculation.

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A very slender 3D body is accurately solved by using boundary element elastostatic analysis in which accurate evaluation of the quasi-singular and the singular integral for a slender element should be considered. This study also shows the validity of the direct regular method (DRM), particularly for the problem of cantilever plates. From this study, it becomes possible to analyze the thin plate as well as the thin cylindrical shell even if the aspect ratio is in the hundreds.

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In this paper, a finite difference method based on integration along bicharacteristics is extended for the numerical analysis of the propagation of a two-dimensional torsional wave in an elastic/viscoplastic circular cylinder composed of several cylinders bonded completely at each end. A numerical example is worked out for the case in which torsional impact is applied to the end face of the cylinder. By obtaining numerical results for various mechanical properties of the cylinders, it is shown that the propagation of the reflected and transmitted waves can be investigated in detail by this method, even when viscoplastic deformation takes place.

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A two-dimensional finite-element analysis was perfomed to study an elastic-plastic singularity of residual stresses in a ceramic/metal joint. The comparison of the elastic singularity by finite-elment analysis with the idealized theoretical results showed that the elastic singularity of residual stresses in the ceramics side was characterized by elastic properties of the ceramics and the insert material. The yielding of the insert material resulted in the change of the singularity. The exponent of the elastic-plastic singularity was larger than that of the elastic singularity. This elastic-plastic singularity can be approximately estimated by a simplified elastic-plastic analysis.

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A Monte-Carlo simulation method for evaluating the tensile strength of the unidirectional fiber reinforced metal matrix composites is proposed on the basis of the elastic-plastic finite element method. In this simulation model, the two one-dimensional line elements representing the reinforcing fibers are incorporated into two sides along the y-axis of a 4-nodes isoparametric element (plane stress), which represents the metal matrix. Furthermore, for estimating reasonably each element stress increment necessary to the fiber-break, the γ_min method is applied to the simulation procedure. This simulation is performed for boron/alumium composite monolayer. The simulated result shows the larger stress concentration around the broken fiber than that of the previously proposed simulation by means of the shear-lag model. Therefore, the former simulation lowers the mean values of tensile strength and increases its scatter, as compared with the later. Such a statistical tendency is in good agreement with the results obtained by comparing the previous experiment with the shear-lag simulation method.

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Bearing strength is most important factor for designing the mechanical joints. Bearing failure is occurred by stress concentration around a hole. It is thought that bearing strength will be elevated by decreasing the stress concentration. In this study, we examined elevatation of bearing strength by thermoplastic film stacking into quasi-isotropic T800/#2500 joints. AE technique was used to investigate failure mechanism and kaiser effect test was performed to investigate the healthiness of materials. We determined that bearing strength was maximum stress during kaiser effect was valid. As a results, it was cleared that the healthiness of specimen was elevated by film stacking. Therefore, it is thought that film stacking is effective for designing mechanical joints. We calculated the shear stress distribution to investigate the influence of film by FEM. As a result, it was made sure that stress concentration was decreased by film.

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In the present study, the effect of the specimen size on the vibrational wave superimposed on the load-deflection curve of polymers is first investigated. Next, in the instrumented Charpy test, a shock-absorbing material is used in order to prevent the generation of the vibrational wave superimposed on the load-deflection curve, and its validity is discussed. Further, differences of the impact response curves obtained by an instrumented Charpy test and the one-point bend test are compared and discussed. The results of this study are summarized as follows. (1) The vibrational wave can be prevented by using a small specimen which shortens the period of the vibrational wave. (2) The load value is lowered by using shock-absorbing material. (3) The differences in the impact response curves and the fracture times obtained from the instrumented Charpy impact test and the one-point bend test are rather large in the lower impact velocity of 3.10m/s; however, the obtained K_Id values are nearly coincidental.

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The present study is concerned with a method for estimating impact load acting on a body of arbitrary shape. It is known that the impact load can be estimated from the impact response of the body by an inverse analysis. In practical situations, the impact response data involves noise caused by the measurement system. Since the inverse analysis is usually ill-conditioned, such noise tends to be expanded and the estimated impact load is obscured by noise. For solving this problem, we show a method to minimize the mean square error of estimation by applying the Wiener filtering theory. We demonstrate the availability of the present method by numerical simulation on the longitudinal impact of the rod.

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Cyclic thermal shock tests were performed on cermets and cemented carbides by heating specimens in a furnace and plunging them into a water bath. The results thus obtained are summarized as follows : (1) The bending strength for the specimens of the cemented carbides subjected to the single thermal shock was larger than those of cermets, while in the cyclic thermal shock tests, the reverse tendency was observed especially in the tests performed at a low temperature difference. (2) In the cyclic thermal shock tests of the cemented carbides, many small cracks were initiated more easily than in cermets at the interface between WC and Co. A remarkable decrease of the bending strength of the cemented carbides subjected to the cyclic thermal shock may be caused by the large cracks formed by the coalescences among these numerous small cracks.

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Under the prevailing quenching method by freely dropping specimens for a thermal shock test of high-strength ceramics, ambient gas is possibly introduced when the specimen is dropped into liquid, causing errors in the evaluation of retained strength and dispersements of measurement data. This paper clarifies that, by observation using a high-speed camera, the ambient gas is introduced when the specimen is dropped into liquid and is attached to the specimen while falling through the liquid, and proposes the dropping method and shape of the specimen which introduces the least ambient gas. Furthermore, it discusses the maximum dropping speed which does not introduce the ambient gas, as well as the influence of the properties of the liquid upon the introduction of the ambient gas. This paper also discusses the influence of the introduction of the ambient gas upon the cooling rate of specimens, and the quenching temperature difference which generates cracks.

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The cyclic deformation behavior in TiNi shape memory alloy under thermomechanical cycling was investigated experimentally, and a constitutive equation was proposed to evaluate the stress-strain-temperature relation. The theory described well the cyclic deformation properties, such as the decrease in the transformation stresses of the martensitic transformation and the reverse transformation, the rise in the transformation temperature of both transformations, the increase in nonrecoverable strain, the decrease in the transformation strain range and the rate of variation in these phenomena with the number of cycles.

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The stress-strain-temperature relation associated with the R-phase transformation in TiNi shape memory alloy was investigated from the phenomenological point of view. A set of constitutive equations consisting of the mechanical constitutive equation and of the transformation kinetics were presented to describe the shape memory effect, the transformation pseudoelasticity and the partial pseudoelasticity. The material constants in the theory were determined from the results of the tensile tests on TiNi wire specimens at various temperatures. The theory described well the stress-strain-temperature relation based on the R-phase transformation.

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The basic characteristics of stress-strain-temperature relation were investigated experimentally as research on the mechanical properties of shape memory polymer of polyurethane series. The main results are summarized as follows. (1) The deformation resistance of the material increases with the number of cycles under the cyclic deformation at temperatures above glass transition temperature. (2) If training is performed before the practical use and the maximum strain is smaller than 100%, the constant recovery strain may be obtained under thermomechanical cycling. (3) The strain obtained at low temperature following the predeformation given at high temperature does not vary under thermomechanical cycling, which shows stable shape fixity of the material for the cyclic deformation.

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The present paper is concerned with the formulation of a viscoplastic constitutive model describing both cyclic hardening and cyclic softening under proportional and nonproportional loading conditions. The history effects of cyclic hardening and softening are also incorporated into the model. We first formulate a parameter and the relevant evolutional equation describing the amplitude dependence of cyclic hardening. Then by using the parameter together with the nonproportionality parameter proposed by Tanaka et al., the evolutional equations of the isotropic hardening variable are examined in detail. The proposed model is established by incorporating these equations into a Chaboche model. To evaluate the adequacy and the accuracy of the model, the experimental results by Bennallal et al. and those by Tanaka et al. are simulated. The predicted results show that the proposed model can describe the cyclic hardening/softening behavior of various complex proportional and nonproportional cycles with amplitude variations and path changes.

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The plastic behavior of SUS304 stainless steel is experimentally investigated at a low temperature of liquid nitrogen (77K), under axial-torsional combined loading conditions. The compressive flow stress is greater than the tensile and torsional stress at 77K. The compressive flow stress subsequent to tensile pre-strain is larger than the pure tensile stress-strain curve, and rises to the pure compressive curve. When torsional loadings are applied after tensile or compressive pre-strainings, the large latent hardening phenomena are observed. The shape of equi-plastic strain surfaces depends on the direction of pre-strains, and can be represented by K_γ (reduced factor).

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The anisotropy of tensile yielding strength σ_Tb in each position of a ABS-resin injection-molded plate was investigated. As the result, the relation between σ_Tb and the tensile direction angle θ in each position was expressed by the following experimental formula : σ_Tb= A₀ + Acos2(θ+α), In this formula, A₀ was constant, being independent of the position in the plate. The values of A and α were measures of the anisotropy in strength and were controlled by the deformation aspect ratio of rubber particles, being dependent of the position of the ABS-resin plate.

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Polycarbonate material used for photoelastic and photoplastic experiments has obvious viscosity. Naturally, the optical properties of polycarbonate material are affected by factors such as temperature, deformation speed and time. In this paper, tensile experiments were carried out to investigate the effect of photoviscoelastit and photoviscoplastic properties, using a tensile experimental machine which is provided with a small electric stove. As a result, it became clear how the mechanical and optical constants, such as Young's modulus E, photoelastic sensitivity a and photoplastic fringe value f_εp, were changed by the different temperatures from 120°C to 155°C with a step of 5°C and the different tensile speeds, i.e., 0.5, 2, 6, 10, 15, and 20 mm/min. Young's modulus E and photoelastic sensitivity a are influenced by both the temperatures and tensile speeds, but the photoplastic fringe value f_εp is only affected by the temperatures and is not affected by the tensile speeds.

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Internal friction in carbon steels at around 17 kHz is studied by means of a sensitive electromagnetic amplitude sensor attached to an ultrasonic fatigue testing machine under a strain amplitude within 10^-3. In this report, characteristics of tensiled specimens and their changes with the lapse of time after working are focused on. The following conclusions are presented. (1) The measurement of internal friction is extremely useful when estimating the progress of the recovery process after plastic working. (2) The internal friction increases with the tensile working of 1∼6% strain, and decreases with the lapse of time after working. (3) The above tendency is much influenced by the temperature at which the specimens are kept. (4) The change of the internal friction of specimens which are quenched at low temperature before working becomes remarkable as the quenching temperature rises. (5) These phenomena can be explained by the interaction between moving dislocations and point defects as interstitial atoms such as carbon.

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Optical measurement of plastic strain with CCD camera was applied to tension-torsion combined loading tests of aluminium tube specimens. The axial elongation and the shear strain were successfully measured with the accuracy of 0.5% strain up to 30% strain range, although the change of diameter was detected by another direct method.

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The fracture toughness (K_IC) of the isotropic graphite was determined for four-point bend bar specimens with chevron notches. Compliance calibration in terms of chevron-notch configurations was determined to obtain the crack resistance curve (K_γ) required for obtaining the correct value of K_IC. Acoustic emission signals were measured for detecting precracking and successive crack growth. Loads and back face strains instead of load point deflection were measured for the calibration. Calculations of the stress intensity for the chevron-notched specimen were carried out based on the assumption of Bluhm's slice model. The results of the interlaminar shear correction (k) were investigated in comparison with the data of other researchers. It was concluded that the k value lay between those of other researchers, and the curve of the K_γ vs crack length was constant in the vicinity of the minimum value of the stress intensity.

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In this paper, the continuously distributed dislocation model method is applied and the crack problems are formulated as the singular integral equations with Cauchy-type kernel. In the numerical calculation, the unknown dislocation densities are approximated by the products of the weight function and Chebyshev polynomials. The accuracy of stress intensity factors obtained by this method is verified by comparing these values with the exact solution and the reliable numerical solution obtained by other researchers. The present method is found to give rapidly converging numerical results not only for internal crack problems but also for edge crack problems.

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A new approach which is effective when applied to energy methods such as finite-element methods is proposed. Using the Taylor-Maclaurin theorem, information from the neighboring nodes can be utilized, and any nth-order derivative is obtained as a continuous unique value. Therefore, utilizing this method for various types of energy principles, convergence to a theoretical value is assured by inceasing the mesh division. By applying this method to the finite-element method based on the principle of stationary potential energy for plate bending problems, satisfactory results are obtained.

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This paper presents a tandem-type substructuring method using a LDU decomposition method of the small-size stiffness submatrices for developing an efficient calculation method of a microcomputer/personal computer-aided finite element method (FEM). This method needs to utilize the disk memory storage unit such as floppy and hard disks in order to store the data of the stiffness submatrices and/or their decomposed ones. Especially, the stiffness submatrices of the storage unit are divided from a substructure stiffness matrix within the limit of the machine memory capacity to be used. The data of the LDU submatrices are placed in the data set of the stiffness submatrices in order to save storage space in the unit. The FEM using the method is applied to an efficient analysis of a three-dimensional elastic block with semi-cylinder notches under tension. Morover, the FEM is available for an analysis of structures of a large-size matrix required for a memory capacity larger than that of the machine itself. This method also contributes to the decrease of memory capacity and central processing unit time in the conventional FEM.

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In order to treat engineering data on computers considering the conversion of their units and the consistency of physical dimensions, a knowledge-based system for the processing of physical quantities using an object-oriented approach is proposed. Some of the concepts for understanding physical quantities as objects are described. The basic consideration for designing necessary classes and their hierarchical structure for the processing of physical quantities in structural engineering is presented. The proposed system works as an knowledge-base of physical quantities, and it is easily implemented into any system for engineering anlysis written in Smalltalk.

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A versatile method for analyzing various antiplane shear problems was presented. The method used here is based on the body force method (BFM) which is a type of boundary method. In this paper, the boundaries of an elastic body are approximated by broken lines to eliminate the necessity of using the numerical integrals. The present method is excellent in accuracy and calculation efficiency, as shown in many numerical examples.

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In a former report, the authors introduced a stochastic theory of propagation of elastic waves in porous media, and proposed a pore reponse function method for nondestructive pore characterization. This study was carried out to examine the applicability of this method to quantitative detection of a hydrogen attack in steels. Preparing some samples of high-carbon steel with different hydrogen exposure times, the effect of the texture damage on elastic waves was investigated. After clarifying the propagation mechanism of ultrasound in hydrogen-attacked steel, we presented a nondestructive technique with a pore response function method for evaluating both the size and area fraction of microcracks produced by the hydrogen attack.

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A method of evaluating an effective failure path of multilayer composite laminates under the off-axial load condition is presented. It is necessary to select the failure path whose occurrence probabilities are greater than others, since the combinations of failure paths of multilayer composite laminates are too numerous to evaluate. The proposed method of selecting an effective failure path depends upon the heuristic procedure based on the branch and bound rule which enables one to estimate the effective failure path whose occurrence probabilities are greater than others. An extended study is carried out in order to calculate the failure probability of a multilayer laminate using the resultant effective failure path. Some numerical analysis based on the proposed algorithm are represented for graphite/epoxy composite laminates.

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