A cylindrical crack is situated at the cylindrical interface between the reinforcement and the interphase, and another at the cylindrical interface between the interphase and the matrix. The material properties of the interphase vary continuously from those of the reinforcement to those of the matrix in the radial direction. All around tension normal to the cylindrical reinforcement is applied to the composite materials. The stress intensity factors are calculated numerically for selected crack configurations.

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Impulse response is analyzed to estimate mode shape of beam structures with multiple damages. Beam structures with multiple damages are modeled as Euler Bernoulli beam. Solution of equation of motion is obtained in Fourier transform. Unknown coefficient of the solution is determined to satisfy boundary conditions. The mode shape of beam structures with multiple damages can be estimated by using eigen vibration of strain response under impulse load. Possibility of damage detection is shown by the analysis of damaged beams.

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In this paper, a one-dimensional dynamic thermoelastic problem in a functionally graded thin film subjected to a uniform thermal shock on a top surface is analyzed, assuming that material constants are considered to be an exponential function of the position. Solving the governing equations for the temperature and elastic fields by applying Laplace transform technique, the analytical solution for the temperature, displacement, and stress which satisfy the initial and boundary conditions is obtained. Based on the obtained analytical solution, numerical calculations have been carried out and the time history of stress is shown graphically for a long time.

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In this paper, a thin film subjected to a thermal shock and a magnetic field intensity on one surface is considered. This problem is analyzed based on the Lord and Shulman's theory of generalized thermoelasticity. The governing equations which contain terms of the magnetic field intensity and the viscosity type damping or the resonance type damping are solved by means of the Laplace transform technique. Numerical calculations have been carried out for a copper thin film. With a numerical result, effects of the damping coefficients and the magnetic field intensity on the time history of stress are investigated.

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This paper deals with a control problem of a thermal stress in a multilayer composite circular disk consisting of a structural layer onto which piezoceramic layers with concentrically arranged electrodes are bonded. When a heating temperature distribution acts on the structural layer surface, the maximum thermal stress in the structural layer can be suppressed by applying appropriate voltages which are obtained by solving a linear programming problem. Material properties of each piezoelectric layer are determined in order to maximize the suppression ratio of the maximum thermal stress when constraints are imposed on stresses in piezoceramic layers. Finally, obtained numerical results are shown in a figure and a table.

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A mixed-mode thermoelectroelastic fracture problem of a functionally graded piezoelectric material (FGPM) strip containing two parallel axisymmetric cracks, such as penny-shaped or annular cracks, is considered in this study. It is assumed that the thermoelectroelastic properties of the strip vary continuously along the thickness of the strip, and that the strip is under thermal loading. The crack faces are supposed to be insulated thermally and electrically. Using integral transform techniques, the problem is reduced to that of solving two systems of singular integral equations. Systematic numerical calculations are carried out and the variations of the stress and electric displacement intensity factors are plotted for various values of dimensionless parameters representing the crack size, the crack location, and the material inhomogeneity. The following facts can be found from the numerical results. The normalized intensity factors are under the great influence of the geometric parameters. The effect of the material inhomogeneity on the intensity factors depends on the geometric parameters.

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This paper investigates the thermoelectromechanical interaction among multi parallel cracks in a piezoelectric material under a uniform heat flow and a uniform mechanical load far away from the crack region. The crack faces are supposed to be insulated thermally and electrically. By using the Fourier transform, the thermal and electromechanical problems are reduced to systems of singular integral equations, respectively. The singular integral equations are solved numerically by using the Gauss-Jacobi integration formula. Numerical calculations are carried out, and detailed results are presented to illustrate the influence of the thermoelectromechanical interaction on the stress and electric displacement intensity factors. The temperature-stress distributions are also presented. From numerical results, we can find that the normalized stress and electric displacement intensity factors are under the great influence of the crack spacing and the number of cracks. Especially, the influence of the thermoelectromechanical interaction on the fracture behavior is complicated when the crack spacing becomes small.

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We have been proposed functionally graded material type electromagnetic wave absorbers (FGM type EM-wave absorbers) for the improvement in absorption performance and material strength. In this study, we investigate a plane-strain thermoelastic problem of the FGM type EM-wave absorbers for a hollow cylinder subjected to irradiation power and convective heat load. The FGM layer with graded composition is considered as a multilayered layer. We present the analytical solutions of electromagnetic fields and irradiation power distributions in the absorbers. Temperature fields are analyzed by modifying Vodicka's method. Elastic thermal stress and thermal displacement are also analyzed based on the stress function method. Numerical calculations are carried out for the FGM type cylindrical absorbers with absorption layers composed of epoxy resin matrix and conductive titanium oxide particles. The temperature and thermal stress distributions in the FGM type cylindrical EM-wave absorbers subjected to asymmetrical heating are quantitatively evaluated.

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This paper is concerned with the theoretical analysis for a laminated hollow cylinder constructed of isotropic elastic material and maltiferroic materials due to unsteady and uniform surface heating. We treat the maltiferroic materials such as piezoelectric and magnetostrictive materials as a linear magneto-electro-thermoelastic material. We obtain the exact solution of the transient thermoelastic problem for the laminated hollow cylinder. As an example, numerical calculations are carried out for a three-layered composite hollow cylinder constructed of isotropic elastic material, piezoelectric material and magnetostrictive material, and the numerical results in a transient state are shown in figures.

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Thermal stresses are repeatedly applied to members due to temperature cycle of heating and cooling. Then, the members often fail due to the repeated stresses as a result of inelastic behaviors and fatigue deformations. This study is concerned with a plane axisymmetrical transient thermal stress problem of a hollow circular cylinder under a cyclic heating. Analytical solutions of temperature change, displacement and stress components in the cylinder are derived. Furthermore, numerical calculations are performed under the condition that inner surface of the cylinder is exposed to a sinusoidally varying temperature, outer one is kept at typical temperature. Repeats of tension and compression in thermal stresses are applied to the cylinder, which are resulted from the temperature cycle. In particular, it's found that normal stresses in circumferential and axial directions of the cylinder are much larger.

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Buckles due to a thermo-elastic buckling in thin-walled strips passed in heating and cooling zones of continuous annealing furnace may be concerned about. This study deals with an analytical development of thermo-elastic buckling of thin-walled strips in order to judge occurrence of buckles in the strips, and to consider means of prevention against the buckling. Making use of fundamental equations of thermo-elastic buckling for a flat plate, a problem of thermo-elastic buckling of a rectangular plate under uniform temperature change is considered. Analytical solutions of critical bucking temperature change for the plate with simply supported edges and strip under uniform temperature change are derived. Effects of dimensions and shape in the plate on critical buckling temperatures in thermo-elastic buckling are discussed briefly.

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This paper proposes a new approach for stochastic homogenization analysis of a particle reinforced composite material considering a random variation of an elastic property of component materials. Especially, a non-uniform microscopic random variation is taken into account. In order to analyze a stochastic homogenization problem considering a non-uniformly distributed random variation, a hierarchical modeling with an intermediate scale is introduced. In order to investigate validity of the proposed approach, stochastic homogenization analysis of a glass particle reinforced composite material is performed. From the numerical results, accuracy of the proposed approach is discussed.

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The mechanical properties of polymer composites reinforced with micro glass balloons are investigated in temperature conditions. The matrix resin of the composite is epoxy resin and its dispersion is micro glassy spherical shells of Sirasu Balloon. The composite system developed is a kind of micro porous materials with lightweight. From the experimental data of bending and tension tests, mechanical behaviors of the composites were examined, and the effects of material properties and fabrication method on the mechanical properties of composites were discussed from the viewpoint of micromechanical study. A homogenization theory with multi-scale analytical method has been applied in order to evaluate the composite material system in temperature conditions. Numerical calculations were performed by using a model of micro porous materials and setting properties of each material at the temperature.

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In this paper, the elastic modulus of the early part and the late part of Japanese cedar is measured by the three methods. These methods are the bending test, micro indentation and nanoindentation. Measured data are compared to each other. It is defined that the measured value by the micro indentation test is smaller than the values by the other two methods. This phenomenon shuld be related to the micro structure of the wood. It is confiremed that the firther study is requierd in order to get distinct mechanism.

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The rotating bending fatigue tests were conducted using wrought magnesium alloy AZ80 with multi-layered DLC film in the laboratory air and in the pure water and the effect of the number of layers and the thickness of the DLC film on fatigue behaviour of the material under corrosion environment was investigated. It is clarified that the multiple and/or thick DLC film is effective to improve the fatigue strength under corrosion environment; however the single and/or thin DLC film is not. It is attributed to the defects in DLC film. In the single and thin DLC film, defects of which the size is 20〜30 μm exist and penetrate to the parent material; however in the multiple and thick DLC layer, defects which penetrate to the parent material were scarcely observed and the DLC layer could fully coat a specimen.-

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This paper describes corrosion fatigue behavior of the anodized magnesium specimens with different thickness to clarify the effect of the film thickness on the corrosion fatigue lives, and to study its mechanism. For these purposes, canti-lever type fatigue tests were conducted in both laboratory air and sodium chloride solution.

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This study investigated effect of plasma-nitriding as pre-treatment and DLC/CrN multi-layer coating on friction and fatigue properties of stainless steel SUS316. The multi-layer coating was conducted using the unbalanced magnetron sputtering (UBMS) method. The result showed that the friction coefficient of the DLC/CrN-coated material in dry condition was higher than that of DLC-coated material. However, the wear resistance of the DLC/CrN-coated material under the condition lubricated by motor oil was improved more than that of the DLC-coated material. The fatigue strength was improved by plasma-nitiridng by 45 % and it was further improved by DLC or DLC/CrN-coating. This result showed that the combination of plasma-nitiriding and the DLC or DLC/CrN coating was effective to improve the fatigue strength.

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In order to investigate the effects of surface polishing for high cycle fatigue property on the laser peened Ti-6Al-4V specimen, the rotating bending fatigue test were carried out with three kinds of the electrical polished(EP) specimen, mechanical polished(MP) specimen and MEP specimen was polished with both polishing. As the results, the fatigue limits of polished specimens were not improved and the fracture surfaces showed characteristic appearance.

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In order to investigate the effect of laser peening (LP) treatment for the fatigue property improvement of friction stir welded A6061-T6 aluminum alloy joints (FSW), plane bending fatigue tests were carried out. Although the surface roughness was increased by LP treatment, the fatigue limit of the laser peened FSW specimen was higher than the fatigue limits of the FSW specimen and the A6061 specimen. As a result of hardness measurement, the hardness in the welding area was especially increased by the LP treatment.

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For predicting fatigue life for SPC270 spot welded specimens using the numerical simulation code "FLARP" based on ΔK_<RP>, some material characteristics have been obtained. Young's modulus, tensile strength, yield stress, and elongation are measured for parent material from tensile test. Vickers hardness and residual stress distribution are measured and metallographic structure is observed. The RPG load and fatigue crack growth rate are essential parameters for the simulation code FLARP, since these are obtained from a specimen with an initial crack under cyclic loading. As a result, material parameters C and m are obtained from the relation between crack growth rate da/dn and ΔK_<RP>. Finally, fatigue life curves are obtained for LT and TS specimens, and crack propagation path is investigated.

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The "FLARP" numerical fatigue crack initiation and propagation simulation code has been applied to the fatigue test of spot-welded SPC270 steel TS and LT specimen. To obtain accurate stress range and residual stress along the assumed crack path, finite element analyses are employed, in which the variation of the yield stress for base, HAZ, and nugget material is considered in detail. The finite element models are also contributed to obtain the relation between crack depth and stress intensity factor of a surface crack propagating along the spot nugget and one that appears on the back surface. The simulation results with well-identified input parameters using measurement value are compatible with the real fatigue test result, which shows that the simulation code is valid for predicting S-N curve of the given specimens.

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A hypothesis of plastic adaptation has been proposed and modeled as one idea that is available to link micro- and macro-scopic approaches to fatigue problems. Based on the hypothesis, an equivalent cyclic stress ratio has been formulated as a parameter for correspondence between cyclic stress conditions of notched and unnotched specimens. In the present study, the rationality of the hypothesis and its application to multi-axial fatigue problems are discussed from a viewpoint of micro-and macro-mechanics.

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A series of tests were conducted in aluminum alloy 2024-T3 to investigate the effect of additional notches on the fatigue behavior of double hole specimens. Basic specimen has double holes and their fracture was interacted with the specimen edge. Within the present study conditions, the longest fatigue life was observed where double hole with shorter distance between each edges and longer distance from specimen edge to holes. The smallest fatigue life was observed where longer distance between the hole edges. This paper described how the improvement of fatigue Me of later case of basic specimen was examined by applying additional notches. The finite element method (FEM) was used to analyze the stress concentration around the basic dual holes and additional notchesin the present specimens.

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The author suggested that fatigue lives of the sharp notched specimens of high strength steels the tensile strength of which was higher than 1000 MPa, could be estimated only by the stress intensity factor and was not depend on the tensile strength. This result indicates that the fatigue life of the sharp notched specimen is controlled by macro fatigue crack growth rate under small scale yielding. It is well known that macro fatigue crack growth rate under small scale yielding depend on Young's modulus. Therefore, the relationship between the fatigue life and the stress intensity factor of the sharp notched specimen is thought to depend on Young's modulus. In this study, K-N curve of metallic glass and non- ferrous alloys were compared with that of high strength steels and E dependent fatigue of sharp notched specimen was experimentally verified. Its importance on fatigue design of machine and structure used high strength light alloys was discussed. Some design methods of avoid fatigue accident were discussed and some future development of simulation method was suggested.

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It was found in the previous study that the fatigue crack growth rate actually accelerated after a tensile overload under negative stress ratio. This behavior is related to the residual stress conditions in front of the cracktip. In the present study, the experimental conditions which lead the accelation of crack growth after the overload were investigated. The materials used were carbon steels, S15C, S35C and S45C. The center cracked plate specimen was employed and the overload was appled duringe the fatigue crack gwoth tests under constant stress amplitude with R=-1. The specimen geometry and stress levels of overload and stress amplitde were related to the acceleration of crack growth after the overload. Therefore, the applying overload could be dengerase in some loading conditions.

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The effect of carbon black loading on fatigue crack growth rate of vulcanized natural rubber used in automotive applications such as engine mounts was studied using pure shear specimens. Tearing energy was calculated from uncut specimens while crack growth rate was calculated from cyclic tests of cut specimens. Finally the fatigue crack growth rate as a function of tearing energy was determined. The fatigue crack growth rate of natural rubber at a given tearing energy was decreased with the increase in fraction of carbon black.

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Piezo-electric ceramics, PZT, are used as actuators in mechanical structures, therefore the log-term reliability of actuators is required. PZT has three types of crystal structure, tetragonal, Rhombohedral, structure and MPB by difference of chemical compositions. In addition, there are two types of PZT(hard and soft) by added element. In this study, 4-point bending tests of the above six type of PZTs were conducted. Bending strength and fatigue crack propagation behaviors were investigated. Fatigue crack propagation rate could be divided into three regions, Region I II and III. Region I is the region where crack propagation rate decreased. Region II is the minimum constant rate region. Region III is the acceleration region. In Region III of high crack propagation rate, crack propagation rates for three crystalline structures obey the Paris's law.

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We investigated the mechanical condition for the irreversible hydrogen desorption under cyclic loading condition using the fatigue crack growth tests and hydrogen visualization analysis. The sample was a cold drawn high strength steel. The fatigue crack growth rate was accelerated by irreversible hydrogen. However, the fatigue crack growth rate in terms of ΔK_<eff> was independent of the stress ratio. To investigate the behavior of irreversible hydrogen near a crack tip and notch root under cyclic loading condition, we applied a hydrogen microprint technique to the fatigue tests. After the fatigue test, silver particles precipitated along the fatigue crack and notch root, and thus this indicates that irreversible hydrogen is desorbed from the trap site not only near the fatigue crack but also near the notch root under cyclic loading. The mechanical condition for irreversible hydrogen desorption was discussed by the finite element analysis and hydrogen visualization analysis.

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In order to clarify the micromechanism of transgranular type time-dependent subcritical crack growth under hydrogen environment (hydrogen-assisted cracking; HAC), a sustained load cracking test using a single-crystalline Fe-3.2wt.%Si alloy was implemented in hydrogen gas. Crack growth rate, da/dt, along (001) plane showed linear dependence on stress intensity factor, K. Same type of periodic striation pattern was observed on the fracture surface irrespective of daldt; striation spacing, AS, was found to be constant over daldt range of five orders, daldt may be related to diffusion of hydrogen at the crack tip.

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In this research, the crack growth behavior was investigated by an ultrasound in order to evaluate a fracture splitting method which has been used in the manufacturing process of connecting rod. The test specimen fabricated similar to the connecting rod used the quenched & tempered S50C steel. We used a surface wave to measure the crack growth length in the test specimens with v-notch fabricated by machining and laser method. In this case, the tensile load added to the test specimen using the tensile testing machine. We compared the crack growth length on both specimens with v-notch. As a result, the crack growth on the specimen by laser method is longer than that of specimen by machining method. Also, fracture splitting on both specimens started at about 80% of fracture load.

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It is important to expand knowledge for low-cycle fatigue properties of pre-strained nuclear component materials and nondestructive inspection (NDI) techniques for fatigue damage detection when considering resumption of nuclear power plant subjected seismic load. As acoustic emission (AE) monitoring can be applied during fatigue test and operation of plants, we conducted AE monitoring during low-cycle fatigue test. The AE monitoring results showed that reduction of fatigue life by applied high pre-strain was caused by shorten of fatigue crack initiation life. The result also showed that the possibility to use AE monitoring for online monitoring of fatigue damage detection.

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Following the previous report, FE analyses on DC electrical potential drop (PD) method were conducted. In order to investigate the applicability of the PD method to high temperature crack growth under combined stress conditions, the effects of crack angle, crack opening displacement and crack bending on the PD were investigated computationally. The calibration of PD method for crack growth under combined stress conditions was formulated. This calibration was applied to the experimental results of high temperature fatigue crack growth tests for stainless steel SUS304 at 650℃. It was clarified that high temperature fatigue crack growth in both tensile type and shear type can be evaluated by this calibration of PD method.

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A fatigue strength diagram is used when we estimate fatigue strength under mean stress or residual stress. The most well-known is the modified Goodman diagram, which connects tensile strength and endurance limit with a straight line. However, a fatigue strength diagram of aluminum alloy is not obvious because aluminum alloy does not have endurance limit-especially at high temperature. Thus, we make up the generalized fatigue strength diagram at N cycles of aluminum alloy at high temperature, using the strength at N cycles instead of the endurance limit, and divide the straight line by fracture feature; plastic deformation and creep. In other words, the fatigue strength diagram of aluminum alloy consists of 3 regions.

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Nylon 6 clay hybrid (NCH) composite consists of nano-sized Montmorillonite and nylon 6 matrix. Tensile tests at near glass transition temperature (35℃, 50℃) were conducted at a strain rate of 10^<-2>s^<-1>. Fatigue tests were performed with a stress ratio of 0.1 and frequency of 0.1 Hz. Although the tensile strength and fatigue strength of NCH-2 are the highest at room temperature, the tensile strength and fatigue strength of NCH-5 become the highest at 35℃,50℃. Fatigue fracture surfaces show different patterns between at room temperature and 35℃,50℃. Fatigue fracture surfaces show that fatigue fracture of NCH-2 is brittle at room temperature, but ductile at 35°C,50°C, while fatigue fracture of NCH-5 is brittle at both room temperature and 35℃,50℃.

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Various kinds of springs are frequently used in mechanical structures and they are exposed in the long term service as a component of the structure. In order to ensure the long term durability, their fatigue properties should be clarified in very high cycle regime. Thus, fatigue properties of a spring steel(JIS Material code: SUP7) were experimentally examined in both of rotating bending and axial loading in this study. Fundamental S-N property was obtained and the fatigue fracture mechanisms were discussed from a view point of fractography.

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In order to investigate the effect of shot peening (SP) on fatigue strength of extruded magnesium alloys, cantilever-type rotating bending fatigue test was performed in laboratory air at room temperature using hourglass shaped specimens of AZ80 extruded (F-specimen) and treated by an artificial aging after extrusion (T5-specimen), which were treated with two SP conditions. From the results, surface roughness induced by SP was sensitive to the fatigue strength of this material. The specimen slightly removed surface roughness showed the improvement of fatigue strength in high-stress amplitude level but not in low-stress amplitude level. Fatigue crack initiation site was changed from surface to subsurface depending on applied stress amplitude by the effect both of compressive residual stress and high hardness on surface layer.

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Magnesium alloy is paid attention as a high strength and lightweight material; however magnesium alloy has a disadvantage of a flammable material. In recent years, the low flammability magnesium alloy (AMCa602) was developed. In order to use this material as structural components, it is necessary to clarify fatigue properties. In this study, fatigue tests were performed for AMCa602 in both rotating bending and axial loading. Such fatigue tests were carried out up to gigacycle regime to examine the very high cycle fatigue properties. Fracture surfaces of failed specimens were observed by means of SEM and fracture mechanism of this alloy was discussed from view points of fractography and fracture mechanics.

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In order to investigate the effect of stress ratio on high-cycle fatigue properties of an extruded magnesium alloy, axial loading fatigue tests have been performed under three testing conditions of stress ratio, R, of 0, -1 and -1.5 at room temperature in ambient atmosphere using hourglass shaped specimens of AZ80 magnesium alloy extruded (F) and T5-againg treated after extruded (T5). A fatigue limit appeared in the F-specimen only under the testing condition of R=0, while that appeared in the T5-specimen under all stress ratios, because of retardation in crack growth by aging microstructure. From detailed observation of fracture surface, crack initiation mechanism changed from the twin deformation induced in high-stress amplitude level to slip deformation induced in low-stress amplitude level, because of a texture caused by extrusion and the particular deformation characteristics of hep lattice structure in a magnesium alloy.

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In order to investigate the coaxing effect, rotating bending fatigue tests were carried out on SCM435 steels with four different heat treatments by means of dual-spindle rotating bending fatigue testing machine. Experimental results thus obtained were quantitatively evaluated by the miner's rule. As a result, coaxing effect was confirmed for T-0, T-160 and T-300 specimens. However, it is not confirmed for T-500 specimen.

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The most suitable condition that the fine crystal layer is produced and influence of the fine crystal layer on fatigue strength of SCM415 are examined. Generation of the fine crystal layer by FPB processing and the SP processing is reported in the past study. However, only a surface small portion can generate the fine crystal layer. In addition, it is hardly examined the influence that the fine crystal layer on fatigue strength. In this study, the most suitable condition that the fine crystal layer was produced throughout the surface was examined first. As a result, it was understood that strain rate and a projection rate influenced generation of the fine crystal layer. From this, it is thought that it is easy to generate fine crystal layer by lengthening projection time in small projection materials.

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Grain growth behaviour in a copper foil was examined under nonproportional (out-of-phase) loading. First, custom-built testing equipment was installed in a closed-loop servohydraulic testing machine to generate nonproportional loading. Then, the grain growth density and grain growth direction under nonproportional loading were compared with those under proportional loading. Even when the normal and shearing stress magnitudes were the same, the grain growth density tended to be low with an increase in the phase shift between them. Grains tended to grow in various directions under nonproportional loading. The grain growth density under nonproportional loading was obtained using the equivalent shearing stress in Tresca theory and it agreed well with the test results under proportional loading. Therefore, the grain growth density is mainly dominated by the maximum shearing stress in the case of nonproportional loading as well as proportional loading.

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Fine Particle Bombarding of Shape Memory Alloy was done to improve the functionality of the material with respect to tension and fatigue strength without compromizing the Shape Memory Effect. The results of our experiments show that the fatigue strength increased by 64% compared to the non-treated sample. More over, we were able to vary the martensite transformation stress with the enfluenced layer being upto a depth of 20μm. The result obtained are due to the thin enfluenced layer as the bulk material remain the same.

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This paper presents probabilistic approach for the fracture strength estimation of brittle material under variable load rate. At first, a probabilistic model was proposed on the basis of the slow crack growth low concept in conjunction with two-parameter Weibull distribution. Next, the four-point bending test was carried out for alumina ceramics under two-step variable load rate. The experiment result was compared with the predictions to verify the validity of the model.

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J-R curves under continuous hydrogen charge were obtained to evaluate the effect of absorbed hydrogen on fracture toughness of low alloy steel. The effect of absorbed hydrogen, loading rate and tempering temperature were investigated. J_<IC> under continuous hydrogen charge condition drastically decreased in the case of very low loading rate. The materials which were tempered at 803K and 843K showed significant reduction of J_<IC>, but reduction of the material tempered at 903K was small. Dimple fracture surface was observed when the loading rate was high. Quasi-cleavage fracture surface was predominantly observed in the tests which resulted in low J_<IC>.

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Ductile-brittle fracture transition of notched polycarbonate plate was studied with respect to the specimen thickness t, notch root radius ρ and the ratio of K_II to K_I As a result, there was a tendency to arise the brittle fracture as increased with t and 1/ρ under mode I loading. However, failure mode of natural cracked specimen, ρ = 0, of thick plate was ductile fracture. Moreover, it was revealed that failure mode was put under the control of ductile fracture as increased with the ratio of μ = K_II/K_I under mixed-mode loading. Caustic pattern formed by the information at the crack tip was obtained, and the ratio of μ was evaluated from the configuration of this pattern.

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This paper describes evaluation process of bending strengths of plasma-sprayed hydroxyapatite(HAp) coatings. Plasma-sprayed HAp coatings are widely used in the fields of medical implant in order to improve the biocom- patibility of substrate alloys in vivo. Their strength is normally evaluated by Indentation-Fracture method (IF method) or shearing tests. However, these results are considerably varied because of the pores on the surfaces of coatings and to accurately discuss the quality of coatings, the effects of pore size distributions on their strengths must be considered. The maximum pore size was then predicted using extreme statistics and modified Saltycov' s method. In order to calculate fracture toughness of the specimen, indentation fracture method (IF) was applied. Fracture probability model were then used to determine the strength of the coating layers.

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Stress corrosion cracking (SCC) behaviour of wrought magnesium alloy, AZ31, was investigated. The SCC tests were performed using CT specimens in 3%NaCl solution under the hydrogen charged conditions, where cathodic potentials were -1.4, -2.5 and -3.0V. According to Pourbaix diagram, the cathodic potentials of-2.5 and -3.0V correspond to the immunity region. Under the immunity condition, hydrogen embrittlement (HE) type SCC occurred where K_<Iscc> was much higher than that of active path corrosion (APC) type SCC. K_<Iscc> of HE type SCC decreased with decreasing cathodic potential. At the cathodic potential of-3.0V, crack growth rate, da/dt, was insensitive to the stress intensity factor.

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The polymeric material is active now by various places in the society. In recent years, the polymeric material more than a metallic material is used, but there is not a lot of data of destruction under various environments. In the study, the CT specimen is produced with polycarbonate (PC), deterioration under the chemical environment is assumed, and it aims at the clarification of the craze phenomenon in the crack tip. To examine changing mechanical properties due to the medicine deterioration, the soaking examination that used the hydrochloric acid was done. And, the craze was caused in the crack tip by using the tension test. The photoelastic method and the method of caustics that was the technique of optics were used as a mode of analysis. It considered it as an evaluation method by using J-Integration value, the craze length and the crack length.

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Although a lot of interface crack problems were previously treated, few solutions are available under arbitrary material combinations. This paper deals with periodic interface cracks in a bonded infinite plate and a central interface in a bonded infinite plate. Then, the effects of material combination and relative crack length on the stress intensity factors are discussed. A useful method to calculate the stress intensity factor of interface crack is presented with focusing on the stress at the crack tip calculated by the finite element method. For periodic interface cracks, it is found that the stress intensity factors are controlled by the bimaterial parameter e alone and increase with increasing ε and relative crack length. For a central interface crack, the relationship between the dimensionless stress intensity factors F_I, F_II and relative crack length a/W are obtained under arbitrary material combinations. It is found that F_I has the maximum value when α=0.2, β=0.3 and minimum value when α=1.0, β=0 independent of a/W. On the other hand, F_II has the maximum value when α=0.1, β=0 and minimum value when α=0.2, β=0.3.

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