The influence of environmental temperature on fatigue reliability at elevated temperature for carbon-fiber reinforced PEEK was examined. Attention was focussed on the mechanism of growth from mesocracks to macrocracks at elevated temperature. The main results were as follows. (1) The fatigue strength of CF 15 and gf 30 materials decreased with increasing environmental temperature. (2) The influence of stress and environmental temperature on fatigue strength bellow the glass transition temperature was represented by the N_f 1/T diagram and S-T (C+log t_r) diagram. Therefore it was suggested that high-cycle fatigue life was could be estimated from these parameters. (3) It was appeared that the temperature rise in the fatigue damage zone was closely related to the meso crack formation process. (4) It was thought that the difference of mesocrack formation between CF 15 material and gf 30 material was reflected in the difference of the activation energy.

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A microstructural effect on the fatigue crack growth behavior of long cracks in cast Ti 47.2 (at%) Al at room temperature was investigated. Various heat treatments were employed to produced by the nearly lamellar, duplex and near-γ microstructures. The fatigue crack growth resistance exhibited by the nearly lamellar microstructure is superior to that of the duplex and near-γ microstructures. This property of the nearly lamellar microstructure is attributed to crack branching, microcracking, and roughness-induced crack closure due to tortuous crack paths and to crack shielding due to crack bridging. The crack propagation behavior strongly depends on its volume fractions of lamellar and equiaxed grains.

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A study has been made of the fatigue fracture mechanism in A6061 T6 metal matrix composite (MMC) reinforced with 5vol.% SiC particulate at room and elevated temperatures. The main results are summarized as follows. (1) Fatigue strengh decreased with increase of ambient temperature. (2) Relationship between fatigue life and temperature followed the Arrhenius rule. Therefore the fracture mechanism was the same, irrespective of ambient temperature. (3) Fatigue cracking of MMC initlated in the aluminum matrix and crack growth was in the shear mode, because the morphology of the fractured surface showed crystallographic facets. Then, fatigue crack growth mode changed from shear to monotonic fracture mode. (4) The transition occurred at the point at which the plastic zone size of the crack tip became larger than the average SiC particle size.

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Fatigue crack growth behavior has been investigated using structural carbon steel (JIS S 45 C) specimens which have single edge or small surface pre-cracks. The crack closure behavior of small surface cracks was dynamically measured by using an interferometric displacement gage with a laser diode. The threshold condition for crack initiation from pre-cracks was found to be given by the constant value of the effective stress intensity range which was equal to the threshold value for long cracks. The crack opening stress intensity factor increased with crack growth. The threshold crack opening stress intensity factor was formulated as a function of for ratio of the applied stress to the yield stress and the increment of crack length. The R-cruve was constructed in terms of the experimentally determined threshold value of the maximum stress intensity factor which was the sum of the range of the threshold effective stress intensity and the crack opening stress intensity factor. The R-curve method was used to predict the fatigue thresholds of the pre-cracked components. The predicted values of the fatigue limit for crack initiation, the fatigue limit for fracture, and the length of nonpropagating cracks agreed well with the experimental results.

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Four kinds of surface hardened specimens having hardened thicknesses of 0.7∼1.8mm were prepared using a"Micropulse induction heating system". Rotation bending fatigue tests were performed with special focus on the effect of hardened thickness on fatigue properties. Measurement of residual stress and observation of the fracture surface were also carried out to investigate the fracture mechanism of the specimen with a shallow hardened layer. It was found that there is not much improvement of fatigue strength at 10⁷ cycles for specimens with shallow hardened layers in spite of having a high compressive residual stress of about 1000MPa. This is because the fatigue cracks originating from inside the hardened layer leads to final fracture of the specimen (internal fracture mode). Improvement of fatigue strength has been achieved by forming thick hardened layers. In this case, fatigue cracks originate from inclusions located in hardened layers, which leads to the final fracture (hardened layer fracture mode).

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The effect of specimen size on static and dynamic 3-point bend elastic-plastic fracture toughness in an aluminum casting alloy, JIS AC4CH-T6, and ferritic ductile cast iron is discussed. It is shown that the factor α in the ASTM valid criterion is 100 under static and dynamic loading conditions for AC4CH-T6 aluminum casting alloy and 66 under static loading and 160 under dynamic loading for ferritic duetile cast iron. The variation of α is considered to be related to the J_IC/σ_fs ratio in different materials under different loading conditions.

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A fatigue test has been carried out at room temperature in air on a carbon steel pipe which has a crack on its outer surface. Special attention was paid to crack growth rate, crack shape and fatigue life. A new equation was proposed for evaluating K after crack penetration. The main results obtained in this study are as follows. (1) Before crack penetration, crack growth behaviors such as aspect ratio and leak life were evaluated using Newman-Raju's equation and plate model. (2) After crack penetration, crack growth behaviors such as crack shape and fatigue life were evaluated using the equation proposed in this paper.

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A computational analysis addressing to the creep crack propagation problems is conducted. An incremental finite element procedure is developed and applied for investigating the creep effect on a fatigue crack propagation of a center cracked plate. The near crack parameter T, for which the preliminary study showed the validity of its use in the elastoplastic creep regime, is used in the prosent fatigue crack study. The phenomena of crack acceleration and retardation due to loading spectra are discussed in terms of T and the crack opening/closure load level. T as well as crack opening levels indicates the acceleration and retardation. The creep crack propagates faster than that under the non-creep cracks. The creep strain seems to play the role of suppressing acccleration and retardation effects in low to high, high to low and single overload cases.

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The major factor dominating creep and creep-fatigue failure at high temperature for SUS304 stainless steel is the nucleation and growth of creep cavities on grain boundaries. In this study, previously proposed cavity growth models for creep conditions were expanded to give models for creep-fatigue condition. The analytical cavity growth rate was compared with experimental data obtained in our prevlcus study. As a result, it was found that the cavity growth process under stress-controlled creep-fatigue conditions continuously observed by the SEM could be explained using the cavity growth rate equation consisting of the sum of constrained diffusion-controlled and deformation-controlled growth rates. Also, a cavity growth mechanism map, which can be applied to various load patterns, was developed based on the models for cavity growth in creep conditions.

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There is a rule of thumb'on thick-walled cylinders, that is'the circumferential fatigue cracks under thermal stress will be arrested at 1/3∼1/2 of the wall thickness'. In our study, the reason why crack tends to arrest will be made clear, and practical formula to estimate arrest point will be proposed. In this paper, effect of thermal stress distribution on fatigue crack arrest is examined, on the case of single edge cracked strip. It was derived that the stress intensity factor distribution is a product of a tunction of structural compliance and the equivalent moment calculated from the thermal stress distribution. From this fact, it was concluded that characteristics of crack growth rate (including tendency of arrest) under cyclic thermal stress is dominated by structural compliance, assuming Paris'Law.

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There is a rule of thumb'for thick walled cylinders, that is'circumferential fatigue cracks under thermal stress will be arrested at 1/3∼1/2 of the wall thickness.'In this study, the reason for this will be clarified and a practical method for estimating arrest point will be proposed. In this paper, the characteristics obtained for a single edge cracked strip, which were reported in our previous paper are compared with those of cylinders with inner surface circumferential crack. From FEM results, it was concluded that cylinders show similar characteristics to those of single edge cracked strips from the standpoint of crack growth rate (including tendency of arrest) under cyclic thermal stress. In addition, thick cylinders always showed a tendency of crack arrest, assuming Paris'Law.

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We previously discussed the crack tip singularities of various kinds of open crack meeting at the interfaces of different isotropic materials for plane problems. Based on these results, this study is concerned with singularities near the tip of an arbitrary open crack terminating at the interface of isotropic and anisotropic materials. Using the eigenfunction-expansion method of Williams, the crack tip singularities for mode I and mode II are computed. The characteristic determinant is derived by the boundary conditions and interface continuity conditions, and is solved directly using Mullers'method, which computes algebraic equations of high degree. The theoretical process of the analysis and some numerical results represented by figures are given.

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In this paper, characteristics of the stress intensity K in a three phase bonded structure subjected to a uniform temperature change are studied theoretically. Material combinations with wedge angles and mechanical properties (Young's modulus, Poisson's ratio and thermal expansion coefficient), in which K becomes zero, are shown on the k₁₂ (stiffness ratio)-ψ₁ (wedge angle of material 1) plane against the thermal expansion coefficients. Also, distribution forms for K are the same as those in the case of a two phase bonded structure. Then, the distribution forms for K in the case of the threephase structure strongly depend on the thermal expansion coefficients of each material. Moreover, the relationship yielding K=0 between the stiffness ratio and the wedge angle, classification of the distribution patterns for K and disappearance conditions of the stress singularity are shown on the k₁₂-ψ₁ plane.

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Three-dimensional finite element analysis has been carried out on the compact normal and shear specimens under mixed-mode loading. The complex stress-intensity factor K associated with an elastic interface crack is discussed via three different approaches : the virtual crack extension method, the modified crack-closure integral and displacement extrapolation. The effect of Young's modulus ratio on stress intensity factors is discussed under various kinds of mixed-mode loading. The distribution of stress intensity factors along the crack front is investigated. A comparison between stress-intensity factor K_I and K_II, obtained by these three methods, is carried out.

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Displacement in the near-crack-tip fields was measured on transparent compact normal and shear specimens under mixed-mode loading by speckle photography. The stress-intensity factors along the crack front were evaluated by the displacement method. A finite element analysis was carried out on the same specimens. The accuracy of stress-intensity factors was discussed by comparison between the virtual crack extension method and the displacement method for mixedmode problems. The experimental results were compared with the numerical results. The variation of stress-intensity factors with load application angle α was discussed on different planes from the free surface to the center of the specimen.

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In this paper, the characteristics of the stress fields for a crack normal to and terminating at a bimaterial interface of anisotropic half-planes are studied as a plane problem. The eigenequaion, by which the order of stress singularity is determined, is given in an explicit form. Th problem contains eight independent elastic constants ; however, it is found that the eigenvalues depend on only three parameters, which are defined as combinations of the elastic constants.

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A three-noded triangular element proposed by Akin, which has a stress singularity of O (γ^-λ), was investigated. A singular element was incorporated into a general-purpose finite element program MARC, in order to analyze the two-dimensional stress field of joints made up of dissimilar materlals. A typical eight-noded isoparametric element was also used to analyze the same problem. Finally, by comparing the accuracy and efficiency of the two example problems, we have shown that Akin's singular element is very useful for the analysis of the stress field at the interface of dissimilar materials.

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This paper deals with analysis of stress in the adhesive layer of bonded shrink-fitted joints subjected to push off forces. The stress distributions in the adhesive layer of bonded shrink-fitted joints and those when the joints are subjected to push-off forces are analyzed as a four-body contact problem using the axisymmetrical theory of elasticity. The effects of the outer diameter and the stiffness of rings on the stress distributions in the adhesive layer are clarified by numerical calculation. Using the stress distributions in the adhesive layer, a method for predicting joint strength is proposed. It is seen that a rupture initiates from the lower edge of the outside surface in an adhesive layer. Experiments on joint strength were performed. The numerical results are in fairly good agreement with the experimental results. It is found that the joint strength increases as the outer diameler and Young's modulus of rings increase. In addition, it is found that the joint strength of bonded shrink-fitted joints is greater than that of unbonded shrink fitted joints.

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Stresses and stiffnesses of band adhesive box section beams subjected to torsional loads have been studied analytically. The influences of pitches and width and thickness of the adhesives on the stress distributions and the torsional rigidities were investigated analytically and numerically. Maximum shear stress in the adhcsives occurs at an intersection of the adhered boundary and the inner edge of flange, and it decreases with increase in the width and thickness of the adhesives. The analytical results were consistent with the results of finite element methods.

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The dynamic strength of an adhesively bonded joint was investigated experimentally. Strength of an adhesive layer and an interface between adhesive and adherend under combined impact loading was measured using the clamped Hopkinson bar method. A tuber butt adhesive joint was used for the experiment. The strength of the adhesive joint was determined by measuring strain transmitted in the transmission tube of the specimen. The dynamic strength of the adhesive layer was greater than the static strength under tensile and shear loads. The time duration to fracture, however, was very short.

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Measurement of mechanical characteristics of materials using the X-Z mode of a Scanning acoustic microscope (230 MHz) was conducted on polymer and other materials. These results were compared with those derived using a conventional ultrasonic probe. For the case in which a SAM was used. SAM was used to determine the velocities of the longitudinal wave in Polymer and surface acoustic wave in metals and ceramics. Theoretical analysis of wave propagation was carried out considering the weight density and an acoustic velocity of water.

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The d.c. potential drop technique based on the use of adjacent probes is applied to the nondestructive evaluation of a crack bifurcated from a nonplanar crack in a rail. The method of evaluation is based on the measurement of the potential drop on the top surface of the rail. The problem of current flow in a material which contains nonplanar and bifurcated cracks is analyzed numerically using a 3-D finite element method. The relationship between the potential drop on the measured surface and the depth of a bifurcated crack is obtained and it is verified in experiments using rail specimens that the cracks can be characterized quantitatively using the 3-D numerical analysis. It is also shown that the sensitivity of the present method using adjacent probes is higher than that of the conventional method in which the uniform current flow in a region far from the crack is used.

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Measurement of stress based on the magnetoelastic interaction effect in ferromagnetic materials relies on a change in permeability due to stress. A method for quantitatively evaluating the stresspermeability relation by combining measured magnetic flux density near a specimen with nonlinear analysis of the magnetic field by a finite element method has recently been proposed. The purpose of the present study is to examine the effect of frequency used for magnetization on the stress-permeability relation. The flux density near the specimen under a condition of loading is measured for various frequencies used for magnetization in a low magnetic field. Coefficients in the equations of the stress-permeability relation are determined for various frequencies using the method for quantitatively evaluating the stress-permeability relation.

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Determination of subsurface residual stresses by X-ray diffraction and layer removal requires correction of the measured stresses. Correction formulas have been developed by the author for tubes with longitudinally nonuniform stress distribution. A simulation is made in order to calculate the influence of random error in the X-ray stress measurement on the results obtained by the formulas, assuming that the random errors are generated by uniform random numbers which have hypothetical values less than ±5% of the maximum residual stress. The simulation shows that the scatter of computed residual stress is also less than ±5%. The simulation is also carried out when the random errors have values less than ±10%. Statistics are briefly discussed.

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A new method is proposed in this paper for determining plastic strains in composite materials using the X-ray diffraction method. The present method was derived by using both Eshelby's approach and the Mori-Tanaka theory to express the stress state in composite materials instead of the elasticity in single-phase materials which is used in the conventional method of X-ray stress measurement. It was found that the plastic strain can be determined from the slope of the linear relation between lattice strains measured by the X-ray diffraction technique and sin² ψ using almost the same procedure as that for determining stresses by the conventional X-ray method. The results on ferritic and austenitic dual-phase stainless steel are shown. We discuss the effects of a uniaxial tensile load in a range of plastic deformation on the field of plastic strain as well as on residual macro-, micro-and phase stresses built up in the sample.

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An analytical solution is presented to the transient temperature field in a functionally graded material plate (FGM plate) heated at its surface. The FGM plate has arbitrary nonhomogeneities of thermal properties and temperature variation only through the thickness. The transient temperature field is determined by solving the nonhomogeneous heat conduction problem in a multilayered plate with piecewise-linear nonhomogeneous thermal conductivity, and different, homogeneous specific heat and density in each layer. Numerical calculations in order to demonstrate the applicability of the present analytical method are carried out for transient temperature distributions in PSZ/SUS304 FGM plates with linear and ceramic-rich compositional distributions.

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The purpose of this study is to develop a topology optimization method to get a given detormation mode, such as a homologous structure. A minimization problem of a square error in relation to a given deformation and an active deformation is formulated for a linear elastic structure. To solve this problem the homogenized elastic constants are employed and a topology optimization is replaced with an optimal density distribution problem. using the similar method proposed by Bendsoe and Kikuchi. The homogenized elastic constants are calculated by the homogenization method for a microstructure having a rectangular hole. Using this method, a structural deformation is controlled to a given deformation. Simple examples are presented to confirm the validity of this optimization method.

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Indentation tests on silicon nitride specimens using a silicon nitride sphere were carried out in order to establish a method for evaluating sphere indentation or impact damage of surface layers and post-indentation residual strength in structural ceramics. The residual strengths of indented specimens were measured by four-point bending tests. The relationship between indentation load and cone crack length was derived from the equilibrium condition of cone crack. Then the residual strength was estlmated from the cone crack length. The estimated values were in good agreement with the was estimated from the cone crack length. The estimated values were in good agreement with the measured values. only in the region of low indentation load where elastic deformation is dominant.

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The bucking strength of the cylindrical part of a reactor vessel is a critical factor in the seismic design of a fast breeder reactor. The buckling design research program has been carried out to establish seismic design guidelines for a fast breeder reactor. The effects of axial load on horizontal seismic responses in pre-and post-buckling states of thin cylindrical shells under horizontal and vertical seismic loads are investigated. Pseudo-dynamic buckling experiments are performed to study the dynamic buckling characteristics of thin cylindrical structures when subjected to seismic loads. The axial seismic loads reduce the lateral load-carrying capacity of the shells in the pre-and post buckling regions so that they amplify the horizontal response displacement. An amplification factor that accounts for the effects of the vertical loads is presented and its validity is verified experimentally.

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Global buckling is an instability phenomenon of a truss structure, which means that the truss structure buckles as a whole, without any structural components buckling. For large-scale, slender-shaped truss structures, such global buckling must be taken into account as well as local buckling (the buckling of a truss member). In this paper, we formulate the global buckling conditions of truss structures of general topologies and propose an analysis method based on linearization. An iterative procedure is also developed for the case in which the geometrical deformation at the buckling point is too large to be neglected. Simulation studies are conducted with column-type and arch-type truss structures and the correctness of the proposed global buckling analysis approach is confirmed. We also discuss the relation between local and global buckling, based on the column-type truss.

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This paper is concerned with the ultimate strength and deformation of steel tubular members subjected to impulsive lateral loads. Simple and explicit formulas for estimation of ultimate strength and deformation are proposed. Dynamical experiments on steel circular tubes have been carried out, and design formulas are derived from the experimental results. When the geometries of the circular tubes and the material parameters are given, ultimate strength, deformation and absorbed energy are easily estimated using the proposed design formulas. Moreover, numerical analyses for the circular tubes are performed using FEM. The numerical solutions for deformations and collapse load are compared with the experimental results. From the results of the dynamical experiments and numerical analyses, the accuracy and applicable range of the proposed estimation formulas are discussed.

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This paper presents an application of the element free Trefftz method to the two-dimensional elastic problem and its shape design sensitivity analysis. The element-free Trefftz method is known as a boundary type solution procedure using the regular T-complete functions. Since the physical quantitles are represented by regular expressions, direct differentiation of the expressions with respect to shape parameters leads to the regular expressions of shape sensitivities. The present method is applied to the relatively simple examples in order to confirm its validity.

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In the pevious paper, we proposed a generalized cellular automata for structural forming, that is a local rule as an analogy of the neural network system. It can be varied for adaptation to different problems. In this paper, a technique for designing large-scale structures using the generalized cellular automata is presented. By setting a small-scale problem that simulates a large-scale structure, a local rule is decided for adaptation to large-scale problems. By using this technique, minimum weight design problems of 2-dimensional continuous structures are analyzed and several solutions to the design problems are obtained.

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An eggshell is craked easily by an inside load, but has strong resistance to an outside load. In this study the structural and material composition of a hen's eggshell is analyzed by microscopic observation, static and dynamic penetration tests and FEM. The results obtained are as follows. (1) From microscopic observation, the eggshell is found to have a laminated structure of many material compositions. (2) The outer eggshell membrane acts as a strong adhesive between the inner eggshell membrane and the eggshell. (3) A cone-type punch and striker makes an initial crack easily, but large penetration energies are required. (4) The penetration energy required from outside of an eggshell is bigger than from inside and consists of the energies required to break the membrane and peel it off the eggshell.

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The effects of the thickness on the ultraviolet (UV) degradation was investigated for polypropylene (PP) and polycarbonate (PC) using"layering-films exposure test." In this test, the films were stacked up as a layer and exposed to UV-light by the weathermeter. After the exposure, tensile tests were conducted for each film. It was found that the failure strain of PP decreased with the irradiation time irrespective of the mask-film-thickness (MFT) although the tendency of the decrease became weaker for larger value of MFT. On the other hand the failure strain of PC decreased only for MFT=0μm. The fractographic observation by SEM and the chemical analysis by the infrared spectroscopy also confirmed that the UV degradation gradually extended along the thickness direction in PP while it was limited on the irradiated surface layer in PC. The decrease in failure strain was correlated to the irradiation UV energy by taking account of the molecular weight change due to main chain scission.

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A Monte-Carlo simulation technique based on a finite element method was developed in order to analyze the strength of a fiber-reinforced plastic matrix composite. The proposed technique can be used to predict approximately the tensile strength distribution of a boron/epoxy monolayer composite obtained experimentally. The effect of the interfacial shear strength on the strength and reliability of boron/epoxy monolayer composites was investigated, using the proposed technique. The results showed that small and large interfacial shear strengths lowered the average tensile strength, and increased the coefficient of variation. Weak interfacial bonds result in the initiation and largescale extension of debonding at fiber breaks, and strong bonds not only cause matrix cracking, but also enhance the stress concentration around the fiber break points. On the other hand, it was clarified that there is an optimal interfacial shear strength which improves the strength and reliability of the composites. Small-scale debonding due to the optimal shear strength increases the cumulative quantity of fiber break, and play a role in increasing the strength and reliability of fiberr-reinforced composites.

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