In this work, a proper subdivided finite-element method (FEM) model was investigated to analyze the residual stress on dissimilar materials. Stress singularity is one of the most important factors in the evaluation of the residual stress distributions. As the results of FEM analysis for residual stress are affected by the subdivided model, calculated stress singularity is compared with Bogy's theory to discuss the reliability of the applied model. With TiB₂-Ni bonding material, the index of stress singularity was analyzed using some subdivided FEM models. It was found that a proper subdivided FEM model existed in which the calculation converged.

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Effects of notch length and fiber content on the tensile fracture behavior of short fiber reinforced polyethylene terephthalate (FRPET) are studied using the acoustic emission (AE) method. The cumulative AE event count and the total AE energy increase with increases in the notch length. The total AE energy decreases with increases in the fiber content, but the cumulative AE event count has a maximum value at a fiber content by volume of 17.3%. The log-log plot of the relationship between the total AE energy and the stress intensity factor has two broken points at Kb and KC which correspond to the changes in failure mode, respectively. The ratios of P_b/P_max are varied, and P_c/P<max> values are roughly constant at the various notch lengths and fiber contents, where the P_b and P_c are loads determined by K_b and K_c, and P_max is the maximum load. The relationship between the damage state at the notch tip and the AE frequency spectrum determines the fracture mechanisms of FRPET at the applied loads of P_b/P_max and P_c/P_max.

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Because of their high specific strength and stiffness, fiber-reinforced plastics have been used as structural members in various fields, and hence analysis of thin laminated structures is important. Postbuckling behaviors of thin laminated plates under uniaxial compression have been discussed by many researchers. However, little research has been performed on the secondary buckling phenomenon for thin laminated plate which occurs with further increase of load. In this paper, the stability condition of CFRP cross-ply laminated plates under uniaxial compression which are simply supported along four edges is determined, using the second variation of total potential energy. The necessity of secondary buckling is proven analytically, and the effects of various factors, such as number of layers, deflection pattern and average axial shortening, are clarified.

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An experimental investigation was conducted to estimate the residual compressive strength of the laminates of carbon-fiber-reinforced epoxy, damaged by penetrative impact loading. After the impact, the specimen was inspected visually and ultrasonically. The effects of impact velocity and stacking sequence of the laminates on the residual compressive strength were investigated.

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In this paper, torsional fatigue tests and additional rotating-bending fatigue tests were carried out on the injection moulded short carbon-fiber reinforced polyamid 6.6 composites. The fatigue mechanism in the composites was clarified through successive surface observations using the replica method. Moreover, the mechanism of the torsional fatigue was compared with that of the rotating-bending fatigue. The fatigue cracks in both fatigue tests are initiated along fibers aligned in the direction of the principal stress. In the case of the rotating-bending fatigue test the fatigue crack propagates finally at right angles to the direction of the principal stress. However, the cracks initiated along the fibers in the torsional fatigue test can not propagate under high-cycle fatigue. On the other hand, the fatigue cracks initiated from fibers aligned in the direction of the principal shear stress can propagate, and reach to final fracture. From the comparison between bending and torsional fatigue tests the fatigue process of this material under the condition of an arbitrary combined stress can be estimated.

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The influence of contact materials on the fretting fatigue strength of 3.5Ni-Cr-Mo-V rotor steel was examined using various contact materials : the same rotor steel, carbon and austenitic stainless steels, and nonferrous alloys of Cu, Al and Ti. Fretting fatigue strength was strongly influenced by the hardness and the elastic modulus of the contact material. The contact opening phenomenon in the neighborhood of the contact edge was clarified by means of contact elastic-plastic FEM analysis. Contact pressure and tangential stress on the fretted surface were analyzed in detail. Maximum tangential stress appeared within 0.01-0.5mm of the contact edge due to the contact opening phenomenon. Fretting fatigue limits for various contact materials were successfully estimated using the tangential stresses obtained by FEM analysis and the unfretted fatigue data of the smooth specimen.

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In this paper, the effect of environmental conditions, especially humidity on the fatigue strength of polymers is discussed. Acrylonitrile butadiene styrene (ABS) and acetal homopolymer (POM)which are seen in industrial applications were used. The observation of fracture surface by SEM and quantitative analysis of the fatigue specimen by scanning acoustic microscope (SAM) were carried out to make clear the influence of environmental conditions. As a result, it was found that ( 1 ) ABS and P0M in high-humidity conditions exhibit a shorter fatigue life than in low-and medium-humidity conditions, and ( 2 ) the fatigue strength of polymer is considered to be influenced by elastic properties of the surface of the specimen. With the measurement of LSSCW velocity, elastic properties at microareas of the polymer became clear.

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In order to study the effect of surface layers formed by lathe turning on the fatigue strength, rotating bending fatigue tests of an annealed carbon steel were carried out. The results obtained are as follows. The fatigue limit of annealed carbon steel specimens turned by a cermet tool, increases by 34 % in comparison with electropolished specimens. Because of work hardening and compressive residual stress in the surface of the specimen formed by lathe turning, crack initiation was restrained. In the specimens formed by turning, a long crack beyond the worked layer size propagated with almost the same speed as that of a crack in the nonworked layer.

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The fracture mechanisms in tensile loading of a fatigued chopped strand carbon fiber. reinforced thermoplastic (CFRP) are examined from the view points of AE count rate, amplitude distribution, and frequency analysis, and compared with those for a virgin specimen. SEM and SAM observations have also carried out. It is confirmed that the peak in the amplitude distribution of AE signals shifts to the higher value side with an increasing of the load and the characteristic relates to the degree of fatigue damage in the previous fatigue test. The phenomenon corresponds to debonding in the chopped tape layer, resin cracking and fiber breaking or pull out of the strand tape, and also recognized the reinforced effect with the strand tape and the fracture mechanisms.

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In the expert system developed for evaluating the fatigue strength of round bar with a notch, two kinds of strength criteria, nonpropagating crack strength and fatigue strength, and two design parameters, notch depth and notch root radius, are adopted. The programming language of the system is C-language. The object-oriented expressions for various types of design knowledge are made, based on the concept of "structure" of C-language. The system is operated in an engineering work station with the operating system, HP-UX.

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Rotating bending fatigue tests of plain specimens were carried out on HIP'ed SMF3035(density :7.83 g/cm³) and CIP'ed SMF3020 (density : 7.09 g/cm³) specimens, in order to investigate the effect of sintered density on the characteristics of the initiation and propagation of a crack through successive observations of the plastic replica method. The following main results were obtained. 1) σ_wo/σ_s of HIP'ed SMF3035 is 0.45 and CIP'ed SMF3020 is 0.39. 2) When σ> σ_wo, in HIP'ed SMF3035 a crack appears in an area having a finite size after some stress repetitions and in CIP'ed SMF3020 a crack appears at the edge of the defect just after stress repetitions. 3) When σ=σ_wo, nonpropagating microcracks are observed on plain specimens of both materials after N-1×10⁷ under a metallurgical microscope. Therefore, the fatigue limit of plain specimens is determined by the limiting condition for propagation of a microcrack.

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Fatigue crack propagation behavior was observed by means of the beach mark method on the fracture surface. In the specimen with perpendicularly intersecting two holes, the fatigue crack was initiated at the internal corners of two holes and propagated from the internal section to the outside. In the first stage of crack propagation, the crack front formed a straight line and the cracked area in the form of a triangle was observed. This shape gradually changed with the crack propagation. In the final stage of crack propagation, a parabola-like crack front was observed. The crack propagation was examined with the change in the cracked area S. The crack propagation rate of the area, dS/dN, was found to be proportional to the area S, and the crack propagation law could be expressed as dS/dN=CΔσⁿS (Δσ is the cyclic stress range, n and C are constant).

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Abstract-This paper considers the impact response of G-10CR glass-epoxy laminates with a crack at low temperatures. Laplace and Fourier transforms are used to reduce the transient problem to the solution of a pair of dual integral equations in the Laplace transform plane. The solution of the dual integral equations is then expressed in terms of a Fredholm integral equation of the second kind. A numerical Laplace inversion routine is used to recover the time dependence of the solution. Numerical results on the dynamic stress intensity factor at low temperatures are obtained and are presented in a graphical form.

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In order to investigate the effect of biaxial stresses due to the combination of plane bending and cyclic torsion on the threshold of mode I small surface crack propagation, the relationship between the threshold stress and crack length under various biaxial stress ratios C was examined using a circular shaft made of carbon steel. The threshold stress intensity factor is constant above some crack length in each C, but becomes lower with the decrease in C. The length of the slipped regionγ_p at the crack tip on the threshold of crack propagation is nearly constant regardless of C. Therefore, if the threshold curve of crack propagation in C = 0 is determined experimentally, the threshold curves in other C can be deduced from the relationship betweenγ_p and C.

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The stress intensity factors of a radial edge crack emanating from a circular hole have been analyzed for an infinite plate heated by a moving circular heat source rotating at a constant angular velocity around the circular hole. The stress solution can be obtained by superposing the stress disturbance by the crack on the transient thermal stresses due to the moving heat source in an infinite plate with a circular hole. The problem is reduced to a singular integral equation which satisfies the boundary condition on the crack face. The numerical results of stress intensity factors are obtained for the case of a thermally insulated surface and a small crack. The effects of the angular velocity and the radius of rotating heat on the variations of stress intensity factors are considered.

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Ceramics are expected to be widely applied as structural materials due to their excellent mechanical and thermal properties such as high-temperature strength, wear resistance and low expansion. In actual fact, ceramics should always be used in combination with metals because of two serious defects of ceramics, i.e., brittleness and hard formability, which are fatal as structural components. One of the key points in joining ceramics to metals is to construct an appropriate interlayer for reducing thermal stresses originating from thermal expansion mismatch between a ceramic and a metal. In this paper, we present an analytical solution for the thermal stress problem in a ceramic/metal composite hollow circular cylinder with an interlayer of Functionally Gradient Material (FGM) subjected to unaxisymmetric heating. The solution is expressed using the thermoelastic theory for the nonhomogeneous multiply connected regions formulated in terms of the stress function by one of the present authors. From the results of numerical calculation, we discuss the effects of the thickness and the composition distribution of the FGM interlayer on the magnitude of thermal stress.

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The stress intensity factors of multiple radial edge cracks emanating from a circular hole have been analyzed for the case in which an infinite plate is step-functionally heated in a circular region near the hole. The stress solution can be obtained by superposing the stress disturbance due to the cracks on the transient thermal stresses due to the heat source in an infinite plate with a circular hole. The problem is reduced to multiple singular-integral equations which satisfy the boundary conditions on the crack faces. The numerical results of stress intensity factors are obtained for the case of two radial edge cracks with equal crack length. The interference effects of the locations of each crack on the stress intensity factors are considered.

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This paper is concerned with a row of equally spaced equal elliptical holes or cracks in a plate subjected to transverse and longitudinal tensions. The analysis is based on the Laurent series expansion method combined with a perturbation procedure. Computations were carried out for various shapes, sizes and numbers of holes, and σ_max was represented as a dimensionless factor S_max based on the maximum stress σ_o for a single elliptical hole. This factor S_max corresponds to the dimensionless maximum stress intensity factor in the case of cracks. For any fixed shape and size of hole, S_max was shown to be linear with the reciprocal of the number of holes. The numerical results were fitted to convenient polynomial formulae. They give reliable values of S_max for arbitrary shapes, sizes and numbers of holes.

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An elastodynamic boundary element analysis of a fast crack propagation test is performed. A propagating crack subject to a time-dependent uniform pressure on its surfaces is considered. The crack speed is determined in such a way that the dynamic stress intensity factor K₁(t, v) is equal to the fast crack propagation toughness K_ID. Caustics in reflection are generated by making the assumption of plane stress. The time variation of the "measured" K_ID is obtained from the diameter of the generated caustics. The K_ID thus obtained is found to depend on crack propagation history due to the transient nature of the elastic stress field near a propagating crack tip. This may explain to some extent the physical meaning of the experimental data showing the dependence of K_ID on crack acceleration.

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Following the theory of linear piezoelectricity, we consider the electroelastic problem of a finite crack in an orthotropic piezoelectric ceramic strip under longitudinal shear. By the use of Fourier transforms, we reduce the problem to that of solving a pair of dual integral equations. The solution of the dual integral equations is then expressed in terms of a Fredholm integral equation of the second kind. Numerical calculations are carried out, and the stress intensity factor and the energy release rate are shown graphically for piezoelectric ceramics.

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This paper presents an analysis of in-plane problems for anisotropic semi-infinite body due to single force, single dislocation, dipole-force, dipole-dislocation, and so forth, with various surface boundaries such as free, fixed and two sliding conditions. Distributions of stresses and displacements under applied singular forces for the above four boundaries are illustrated by some graphical representations as numerical examples.

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This paper presents an analysis of bending problems for isotropic semi-infinite plate due to single moment, single-point discrepancy of slope deflection, dipole-moment, dipole-point discrepancy of slope deflection, and so forth, with various supported edge conditions such as fixed, free, simply and sliding supported edges. Distributions of bending moment and slope deflection under applied single moment for the above four supported edges are illustrated by some graphical representations as numerical example.

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The macroscopic elastic behavior of polycrystalline metal subjected to tension is examined by two dimensional FEM simulation. The grain is modelled by a regular hexagon in which elastic constants, such as modulus of elasticity, are constant and given as a function of the angle between load direction and crystal direction. In the FEM analysis, each grain is assumed to be homogeneous and isotropic. The macroscopic elastic constants are obtained from the conception of gauge lengths set up in longitudinal and lateral directions. From the results, we can specify the size of the polycrystalline metal, where the macrcoscopic elastic constants are not affected by microstructure (grain size) ; i. e., the metal can be considered as macroscopically continuous.

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When an isotropic solid cylinder is initially in static equilibrium under the action of uniform radial pressure on its surface, a stress wave occurs at the surface the moment the radial pressure is suddenly removed. 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 stress is relatively small. This phenomenon is called the stress-focusing effect. This paper analyzes the effect of these waves precisely. The results give clear indications of the mechanism of stress-focusing effect in an isotropic solid cylinder by using the mathematical formula.

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A functionally gradient material which decreases thermal stresses has been developed for structural components and/or mechanical elements in fields such as nuclear, aircraft and space engineering. Steady-state thermal stresses in a plate made of the functionally gradient material are discussed. The main theme of this subject is to determine the available temperature region where the minimum factor of safety is one or more, and how to distribute the components of the material in the functionally gradient material to decrease thermal stresses, for different mechanical boundary conditions. We discuss a two-layer laminated plate and functionally gradient material plate whose components are ZrO₂ and Ti-6Al-4V. The optimal functionally gradient material plate, which makes the minimum stress ratio largest, is determined for each mechanical boundary condition.

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The stress-strain-temperature relationship associated with the R-phase transformation in TiNi shape memory alloy was investigated experimentally and theoretically. The main results were summarized as follows. ( 1 ) The R-phase transformation showing a clear yielding stage on the stress summarized as follows. ( 1 ) The R-phase transformation showing a clear yielding stage on the stress-strain-temperature relationship appeared in a certain range of shape memory processing tempera-temperature plane almost overlapped each other. Both transformation regions were small for high shape memory processing temperature. ( 3 ) The constitutive equation considering the volume fraction of the R-phase described well the deformation behavior, such as the shape memory effect, pseudoelasticity and partial pseudoelasticity.

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In order to evaluate the effects of the instantaneous strain rate and the structural state reflecting the strain rate history upon the dynamic flow stress, strain rate reduction tests are conducted for high-purity polycrystalline aluminium in a strain rate range from about 8000 to 20000/sec. For the strain rate change tests in such a very high strain rate range, a very steep change in the strain rate is required for the loading system. A new apparatus is devised by which a sharp reduction in the strain rate can be obtained. It is confirmed that the instantaneous strain rate plays a more important role than the structural state in the flow stress at very high strain rates where a steep increase in the strain rate sensitivity of the flow stress is observed.

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This paper describes an application of a hierarchical neural network (HNN) to design technique of an adaptive structure. HNN is used to estimate the adaptive design solutions of a statically determinate truss structures (SDTS) subjected to variable load conditions. The learning data of HNN, i. e., the beam length of SDTS and the load condition, are calculated using the 9eneralized reduced gradient method and thd maximum stiffness law. The effectiveness of HNN for the design of adaptive structures is presented for several numerical examples.

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This paper presents a new efficient calculation method comprising the following two methods:( 1 ) the double-tandem-type substructuring method as an efficient calculation method and ( 2 ) the parallel calculation process for composition of small-sized stiffness submatrices in ( 1 ), in numerical solution of a microcomputer/personal computer-aided finite element method (FEM). The parallel calculation is carried out on several microprocessors, so-called transputer in order to decrease the time required for composition of the stiffness submatrices. This method requires the utilization of disk memory storage units 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 the structure stiffness matrix within the limit of the machine memory capacity. 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 the analysis of a three-dimensional elastic block with semicylindrical notches under tension. Therefore, the FEM is applicable for analysis of structures of a large-size matrix requiring memory capacity greater than that of the machine itself.

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In spite of the importance of determining the specimen boundary in experimental stress analysis, no efficient or successful method for extraction of the boundary contour deformed under load in photoelastic image data has yet been proposed because of several difficulties both in the construction and drawing of an approximate plane curve. This paper discusses a new method for plane curve fitting by use of a plane spline function (PSF) and its automatic drawing only from a small number of selected data points, extending the well-known spline function method of one variable into a new planar spline function method of two variables. In this method, separating the boundary contour into several branches of a simple arc, an algebraic plane curve is fitted to the set of dispersed data invo1ved in each branch. Then, the boundary contour of the specimen edge is efficiently constructed and drawn on the basis of the concept of Frenet's dynamic frame.

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It is very important to study the electromagnetic field around a linear motor car (MAGLEV), not only for predicting performance characteristics, but also to protect passengers from the strong magnetic field. In this study, three-dimensional finite-element analyses were applied to solve the governing equations, and the results were compared with experimental data. It was shown that the computational results satisfactorily agreed with the experimental results. Using the Newton-Raphson method, nonlinear analyses were also applied to study the shielding effects of a steel plate. From these results, it can be said that the finite-element analysis is the most powerful method by which to design the electromagnetic field of a linear motor car.

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This paper deals with a two-dimensional stress analysis of a butt adhesive joint with rigid fillers in the adhesive subjected to a cleavage load. Similar adherends were replaced with finite strips, and an adhesive was replaced with a finite strip including rigid fillers. The analysis was done using the two-dimensional theory of elasticity in order to evaluate the joint strength. The effects of the location and size of rigid fillers on the stress distributions around the fillers and at the inter face were shown by numerical calculations. An experiment concerning the strains of adhesive was performed. The analytical result was consistent with the experimental result. It was seen that with an increase of the shift of location and size of fillers, the joint strength increased more than that of the joint without a filler. The stress singularity at the edge of the interface was discussed.

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