In order to investigate the scatter characteristics of growth rate for small cracks, rotating-bending fatigue tests of smooth specimens were carried out using 0.21% carbon steels with different ferrite grain sizes. Fifteen to eighteen specimens were fatigued at each stress amplitude, and the growth rate of a crack which led to the fracture was measured for all the specimens. The growth data were analyzed statistically. The results show that the growth rate for each crack length can be expressed by a three- or two-parameter Weibull distribution. The CV, coefficient of variance, for crack growth rate distribution was calculated, and using the CV the relations between the scatter in growth rate and the ferrite grain size were investigated.

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To investigate the fatigue behavior of bonded ceramics, Si₃N₄/Si₃N₄ and Al₂O₃/Al₂O₃ joint specimens were three-point-fatigue-tested under static and cyclic loading at temperatures ranging from 300 to 1038K in air. Fractographic observation was also carried out using SEM after the fatigue test. Restriction of the strain in the joining layer due to the difference in Young's modulus between ceramics and metals causes triaxial tension in the tension side of the joining layer, accelerating the formation of small cavities. Therefore the process of strength degradation owing to fatigue is controlled by the rate of either the cavity growth or the crack growth, depending on which one is dominant. At low temperatures, the fatigue process is mainly controlled by crack growth ; on the other hand, formation of small cavity and its growth seem to be predominant factors in controlling the fatigue process at high temperatures. Therefore, the triaxial tensile stress component is a very important factor in evaluating the fatigue life of joints at high temperatures. However, a fairly good estimation of the fatigue life is obtained using nominal bending stress in the present investigation. It is also found that the fatigue life can be estimated using the bending strength of Joints.

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Fretting fatigue tests were carried out using HIP-sintered silicon nitride to study the effect of relative slip amplitude between the specimen and the contact pad on fretting fatigue behavior. Fretting fatigue strength decreased with increasing relative slip amplitude. Application of static contact without fretting motion had no influence on static fatigue strength. Therefore, fretting action with relative slip is essential for the degradation of fatigue strength. Fretting fatigue life prediction based on fracture mechanics analysis was also carried out, where the frictional force between the specimen and the contact pad was taken into consideration. The predicted fretting fatigue lives agreed well with the experimental results.

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This paper deals with the two-dimensional thermoelastic contact problem of a rolling rigid cylinder of specified shape, which induces effects of friction and heat generation in the contact region, moving with constant velocity in an elastic half-space containing two surface cracks located close to each other. In the present temperature analysis, the speed of the moving heat source is assumed to be much greater than the ratio of the thermal diffusivity to the contact length. The problem is solved using complex-variable techniques and is reduced to a pair of singular integral equations which are solved numerically. Numerical results of stress intensity factors are obtained for the case of two parallel cracks. The variance in interference effects on the stress intensity factors with distance between two cracks, and the effects of the frictional coefficient, the sliding/rolling ratio and the distribution of heat generation on the results are considered.

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At present, materials with small dimensions such as thin films are often used in electronic packaging. This study concerns a film fatigue testing method, which makes it possible to observe the fatigue crack propagation behavior on a film bonded to a through-hole in a base plate subjected to push-pull cyclic loads. An analytical model for this testing method is presented using a boundary element method, so that the film fatigue fracture can be treated quantitatively in terms of fracture mechanics (K-values and J-integrals). The fatigue crack growth properties were examined for commercial-grade iron films with 100μm thickness bonded to either a circular or an elliptical hole in the base plate. As a result, using the stress intensity factor based on the measured crack opening displacement, ΔK_est, the fatigue crack propagation behavior of the film could be understood in terms of the effective stress intensity factor widely used in the bulk specimen, ΔK_eff.

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In this paper, the axisymmetric torsion problem of a compound infinite cylinder with an external annular crack is considered on the basis of the three-dimensional theory of elasticity. This problem is reduced to the solution of an infinite system of simultaneous equations. The coefficient matrix is given by the product of three matrices including an inverse matrix. Numerical results are illustrated for the distributions of displacement and shear stress and for the variations of the stress intensity factor K_III for various ratios of inner to outer material shear modulus and various ratios of inner to outer radius of the cylinder.

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The stress development mechanism during local thermal oxidation of a silicon substrate is discussed based on the predicted results using a two-dimensional thermal oxidation process simulation program OXSIM2D developed by the authors. Predicted stress change during the oxidation agrees well with the measured data obtained by means of micro-Raman spectroscopy. There are three main factors which play important roles in stress delelopment in the newly grown oxide film and the substrate. They are the volume expansion of the oxide film, the viscosity of the oxide film, and the bending of the silicon nitride film which is used as the oxidation barrier. These factors give rise to the complicated stress distribution and the stress change near the edge of the nitride film during thermal oxidation.

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In this study, internal stresses of an elliptical ring sector with the cross section of a multi connected region composed of two confocal ellipses, subjected to pure bending are analyzed. Gohner's method is used for analysis and therefore, some difficulties caused by elliptical coordinates are eliminated. The analysis is limited to determining the first correction to the initial stress state for pure bending of an elliptical ring sector with the cross section of two confocal ellipses.

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We present results of a solution to longitudinal impact of thick bars, obtained via an exact three-dimensional theory. Detailed investigation of the behavior of the solution has been carried out, including a number of subsidiary calculations. The results obtained made it possible to improve on the knowledge of the physical nature of the problem investigated. By comparing the exact theory with calculations performed in terms of an elementary bar theory, the successive transition from a three-dimensional (3D) description to a one-dimensional (1D) one could be demonstrated. The obtained dependences of displacements and stresses have been compared with Skalak's asymptotic solution and with results of experiments by Miklowitz.

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A new kind of finite element method is presented for analyzing dynamic behavior of viscoelastic materials. In this method, the finite element formulation can be accomplished in a simple form based on the correspondence principle between elasticity and viscoelasticity. Namely, the finite element equations for a viscoelastic problem are found by applying the Laplace transform to those for the corresponding elastic problem and then replacing elastic constants by viscoelastic functions. Laplace transforms of the nodal displacements can be obtained by solving the matrix equation represented in the Laplace domain (complex s domain). Laplace inverse transformation is subsequently performed with the FFT (fast Fourier transform) algorithm to obtain solutions in the time domain. The present method is successfully applied to analyze some typical problems, and the numerical results show the adequacy of the method.

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A numerical method is presented to analyze three-dimensional stress waves in an elastic/viscoplastic thick plate, when oblique impact is applied to the surface of the thick plate at various impact angles. For the numerical analysis, the finite difference method based on integration along the bicharacteristics is employed. From the numerical results obtained for various loading conditions, the effect of the impact angle on impact fracture is examined. It is also demonstrated that the dynamic behavior of the plate due to oblique impact can be examined in detail using this method.

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The present paper is concerned with a numerical and experimental investigation of the transient torsional waves in a semi-infinite stepped circular bar subjected to torsional impact loading at its free end. The differential equations governing the dynamic torsional deformation of the stepped bar are solved by means of the method of numerical integration along bi-characteristics. The stability and convergence of the numerical solutions are checked by estimating the total energy of the system. The torsional elastic wave-propagation experiments for the stepped bar are performed using a modified version of the torsional Hopkinson bar apparatus. The numerical results for the torsional shear strain-time profiles on the surface before and after the discontinuity of cross section of the stepped bar are shown to be in reasonable agreement with the experimental results. The limitations of the classical one-dimensional torsional wave equation for thin rods are examined by determining the two-dimensional distributions of the dynamic torsional shear stresses in the vicinity of the discontinuity of the cross section of the stepped bar.

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Many automatic mesh generation methods for the finite element method (FEM) have been reported. However, for the case of complicated heat generation, a large number of data depending on the position must be added to the mesh data. Other examples, which also need a large number of data depending on the position, are functionally gradient material and biomechanics. In these cases, it is difficult to prepare the distributed data. This paper shows that these problems can be solved by using an improved multiple-reciprocity boundary element method. In this method, contour lines of distribution are used and these distributions are assumed to satisfy the Poisson equation approximately.

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We discuss the accuracy of finite-element solutions for metals possessing domi-nant plasticity, resulting in an incompressible response in a large deformation field. It is known that poor numerical solutions are obtained for the constrained problem due to incompressibility of deformed metals, but they can be improved by selecting an appropriate shape function and numerical integration technique, as well as by applying the mixed method derived from Lagrangian multipliers. Many studies have been made for rigid-plastic finite-element solutions so far, but large-deformation elastoplastic structural analysis is rarely discussed in the literature. In this work, we discuss the advantages of such techniques in large-deformation analysis using the Jaumann stress rate and isotropic hardening hypoelasticity model.

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The basic deformation properties of pseudoelasticity and shape memory effect due to martensitic transformation and R-phase transformation were investigated experi-mentally for TiNi shape memory alloy (SMA) wire subjected to various maximum strains. The properties of transformation temperature were discussed based on differential scanning calorimetry. The main results are summarized as follows. ( 1 )The deformation properties of pseudoelasticity and shape memory effect were deter-mined based on a stress-temperature phase diagram in which stress and temperature were variables. The stress-temperature phase diagram is useful for the design of SMA elements. ( 2 ) If maximum strain was in the martensitic transformation region, both reverse transformation stress and reverse transformation temperature were almost constant. If maximum strain was in the upswing region after completion of the martensitic transformation, reverse transformation stress decreased and reverse transformation temperature increased with an increase in maximum strain, resulting in the shift of the reverse transformation lines downward and to the right.

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Tensile tests with loading and unloading under various strain rates ε^^· were performed for TiNi shape memory alloy wires at various constant temperatures. The influence of strain rate on the stress-strain-temperature relationship was investigated. The main results are summarized as follows. ( 1 ) For ε^^· < 10%/min, the martensitic transformation stress and its reverse transformation stress did not depend on ε^^·. These stresses were almost constant in the transformation regions. ( 2 ) For ε^^· ≥ 10 %/min, the martensitic transformation stress increased and its reverse transformation stress decreased with an increase in ε^^·. These stresses fluctuated in the transformation regions. ( 3 ) The influence of ε^^· on the transformation stress due to R-phase transfor-mation was slight. ( 4 ) The recoverable strain energy density depended slightly on ε^^· but increased significantly in proportion to temperature. The dissipated strain energy density depended slightly on temperature but increased in proportion to ε^^· for ε^^· ≥ l %/min. ( 5 ) The influence of t on deformation properties is important in the evaluation of mechanical properties of shape memory alloy elements.

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The flow stress in tension after torsional prestrain, for example, is higher than that in pure tensional loading. This phenomenon is called cross effect, cross hardening or latent hardening. In the present study, the cross effect is investigated with torsion-tension combined loading tests. It is observed that the cross effect as well as Bauschinger effect is a kind of delayed phenomenon due to a change of the loading direction. We propose a model that unconstrained Orowan loops around pile-ups that were produced during preloading work as forest dislocations against moving dislocations on intersecting slip planes during subsequent loadings. Since the density of forest dislocations determines the flow stress, the free Orowan loops cause the cross effect during cross loading as well as the Bauschinger effect during reverse loading. The above explanation for the cross effect is confirmed by tension tests after forward and reverse torsional prestrains.

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In order to evaluate the mechanical properties of a very thin film, this paper proposes a convenient method for separately determining Young's moduli of two thin films of a magnetic recording medium. Furthermore, the particular stress distribution inside a magnetic recording film (two bonded thin films) is analyzed. The internal stress in the medium is not uniform when the medium is subjected to unidirectional tension. The analysis shows that the difference in Poisson's ratio on two thin films causes flexure of the two bonded films under tension, as well as shearing stress at the interface between the magnetic layer and the substrate. Since the shearing stress may cause fatigue damage of the tape edge, detailed FEM analysis on its distribution is carried out.

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In the previous work, strain rate change tests were conducted for high-purity polycrystalline aluminum at very high strain rates. Here we present the results of reduction tests carried out for copper. The experimental apparatus devised in the previous work is used to attain a sufficiently steep reduction in the strain rate. The flow stress obtained from the reduction tests is analyzed by means of the deconvolution method. The results indicate that the instantaneous strain rate plays a more important role than the strain rate history for the dynamic flow stress at very high strain rates where a steep increase in the strain rate sensitivity of the flow stress is observed. The above-mentioned results are the same as those found in the previous work.

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To clarify the effect of flaws in the coating film on fatigue strength, cantilevertype rotating-bending fatigue tests were conducted in air and in saline solution (3.0% NaCl) using specimens of 0.37%C steel with flaws in the coating of titanium nitride (TiN) thin film coated by PVD and CVD methods. Flaws in the coating film on the specimen surface were introduced by the application of 1.1-1.6% static tensile strain before the test. An obvious decrease in fatigue life of the specimen with flawed coating film was observed in both environments, as compared with that of an uncoated specimen and a specimen with unflawed coating film. This behavior was marked for fatigue in air, that is, the decrease of fatigue life was 90-75% in air as opposed to 70-50% in saline solution. Although film thickness was 3-5μm, the flaw in the film had the same effect as a notch at which cracks initiate on the substrate. Many cracks were induced in the substrate directly under a flaw and coalesced into a large crack at an early stage of fatigue in air. In corrosion fatigue, corrosion pits at which cracks initiate occur on the substrate under a flaw at an early stage of the fatigue process, and the incubation period prior to the formation of pits does not occur.

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