The simulation of Lamb wave propagation is an efficient tool to improve the accuracy of nondestructive inspection of metallic plates by ultrasonic methods. However the widely used modeling techniques such as FDM, FEM and BEM require too much computation time. Since the Lamb wave technique is often used for large structures relative to the ultrasonic wavelength (e.g. fluid pipes, storage tanks etc.), its computing requires a huge number of nodes or elements which are nearly proportional to computation time. This study is therefore focused on the Hybrid BEM (HBEM), which is the combination of exact Lamb wave theory and BEM for two-dimensional elastodynamics. In HBEM much less nodes should be considered in the calculations, and it results in much shorter calculation time. A description of HBEM used for Lamb wave simulation is given in this paper. The parameters for the exact solution of Lamb wave propagation were optimized to achieve the shortest calculation time. Finally, an effective simulation of a large structure is presented under pre-determined conditions.

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A computer code was developed for continuous simulation of dislocation density in a bulk single crystal during the Czochralski (CZ) growth process. In this computer code, the effects of crystal anisotropy such as the elastic constants and the slip directions were approximately taken into account by averaging the Young's modulus, the Poisson's ratio and the resolved shear stresses along the azimuthal direction. Axisymmetric finite element analysis can be applied to quantitative estimation of dislocation density during single crystal growth process by using this averaging technique together with the Haasen-Sumino model as a creep constitutive equation of a single crystal at elevated temperatures. Dislocation density analyses were performed both for [001] growth direction and [111] growth direction of InP single crystal. As a result, although the [111] growth direction has the higher average Young's modulus than the [001] growth direction, the former gives lower dislocation density than the latter. This result represents the effects of crystal anisotropy and is consistent with the previous qualitative analysis and steady state analysis of dislocation density.

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Composite materials are more and more frequently used in various engineering fields due to their high performance. In the structural design using composite materials, therefore, it is essential to clarify the fracture mechanism, where microscopic fracture, such as fiber rupture or interface failure, can not be ignored. On the other hand, the homogenization theory, on which much attention is paid recently, is one of the attractive methods that can evaluate not only macroscopic but microscopic structure. The objective of this study is to develop an analysis method to simulate the macro- and microscopic fracture propagation simultaneously and to clarify the fracture mode transition of CFRP in the tensile test. This study is composed of two parts. In the first part of this study, finite element formulation in conjunction with homogenization theory including pseudo three dimensional analysis model for CFRP is briefly introduced and in the second part, the new algorithm to simulate the macro- and microscopic fracture propagation using the homogenization method is proposed.

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A great number of functional evaluations may be required until convergence in the process of optimization. Although approximation models constructed by the response surface methodology, which may greatly save the function evaluation, is usually used to get optimal designs, it is thought that the design accuracy may be dependent on the type of activation functions and the design region of interest. In this paper, techniques to search the region of interest containing the global optimal design with designs selected by random seeds, and techniques for finding more accurate approximation using Holographic Neural Network (HNN) is investigated. Furthermore, the mapping method of extrapolation is proposed to make the technique available to general application in structural optimization and formulas to estimate the necessary function evaluations for functions under certain condition is presented. Application examples show that HNN may be expected an potential activate and feasible surface functions in response surface methodology than the polynomials in function approximations. Finally, the real design example of a vehicle component crash worthiness is used to show the effectiveness of the proposed method.

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The adaptively shifted integration (ASI) technique is applied to the explicit finite element analysis of dynamic collapse behaviors of impulsively loaded framed structures. In the present study, the linear Timoshenko beam element is employed, considering the effect of large deformation by the total Lagrangian approach. Numerical studies are conducted for several impact problems. The obtained solutions are compared with the conventional finite element solutions to discuss the validity of the ASI technique in the explicit large deformation analysis. In some of the examples, the folding behaviors of axially crushed members in the framed strucure are approximated by the rigid-plastic solutions for the mean crushing load to attain higher computational efficiency.

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To accurately analyze temperature field and thermal stress problem with contact surface, the effects of thermal resistance of contact surface must be taken into consideration. Most studies on thermal contact resistance problem have been carried out for especially such critical structures as space equipment and nuclear plant, and the others were devoted to some special contact conditions whose contact pressure was less then 5MPa. In this paper, thermal contact resistance is measured with an infrared thermography system for contact surfaces composed of common structural members, where the contact pressure and surface roughness are varied over a wide range. In addition, an empirical equation is proposed to evaluate the thermal contact coefficient for common engineering materials in an atmospheric environment. As an application of engineering problem, a contact temperature field in a bolted joint is analyzed using finite element method as a heat transfer problem with contact surface, and the validity of the empirical equation proposed here is ascertained by comparing with experimental results.

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This paper describes the effect of elastic-plastic material constants on Brinell hardness. Finite element analyses simulating Brinell hardness were carried out by varying Young's modulus, yield stress and work hardening coefficient and exponent. Meyer's rule, P=kd^m, was confirmed to hold by the analyses but the constants k and m were functions of the materials constants. A new equation which can predict Brinell hardness was proposed by knowing the elastic-plastic material constants. The equation predicted Brinell hardness within ±15% error for the analytical and experimental results. Critical thickness defined in JIS for Brinell hardness tests was found to be inadequate and a new guide line was proposed.

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This paper presents γ- and hγ-adaptive boundary element methods. The error analysis is done by the sample point error estimation scheme. Then, the extended and the global error indicators are defined by combining the computational errors and the fundamental solutions. Mesh refinement is carried out so that the error indicator distributes almost uniformly on whole boundary elements at the refined mesh. The present method is applied to the two-dimensional elastic problem in order to confirm its validity.

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The present paper describes the formulation of the free mesh method (FMM), proposed by Yagawa and Yamada, applied to the elasto-plastic large deformation problem. FMM employs Node-by-Node concept, which differs from Element-by Element concept used in the conventional finite element method. In FMM, the tentative triangular finite elements are created around the node, thus information between nodes and elements is not required as input data. The information of stress and strain necessary in evaluating stiffness matrix is transformed from element to nodes and stored in the nodes. The present paper shows the numerical feature of FMM in elasto-plastic large deformation problem through shear loading problem.

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The elastic-plastic stress field near the interface edge with arbitrary bonding angle in bonded linear hardening materials is analyzed, based on the total strain theory and the extended Goursat's stress function. The results show that the stress also becomes singular near the interface edge if the linear hardening is assumed. It is found that the eigen-equation to determine the singular order has the same form as that for the elastic case, where the definition of the Dunders'parameter is modified for the elastic-plastic case.

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In the present paper, the influence of thermal environment on Mode I and II interlaminar fracture toughnesses in unidirectional carbon fiber reinforced plastic (CFRP) Laminates is considered experimentally based on thermoviscoelastic property of matrix resin. Mode I and II interlaminar fracture toughnesses were measured by double cantilever beam (DCB) test and end notched flexure (ENF) test from-100°C to 200°C, respectively. The specimens were made of prepreg of unidirectional carbon fiber/epoxy resin. As the results, Mode I fracture toughness decreases slightly with increasing temperature. Near the primary glass transition temperature of matrix resin, the fracture toughness has extreme value and over the temperature it falls down rapidly. On the other hand, Mode II interlaminar fracture toughness decreases roughly except primary and secondary glass transition temperature where the fracture toughness has a peak.

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This paper presents experimental observation and its modeling of damage initiation and growth in textile composites. Microscopic damage progress was observed by a replica method and a microline method for plain-woven glass fabric reinforced vinyl ester composites. Transverse cracks in the weft occurred first, and then several fiber breaks were observed in the warp. Delamination growth was then observed from the tips of transverse cracks. Evolution of transverse cracks, the stressstrain curve and reduction in Young's modulus were predicted by a shear-lag analysis. It was found that the prediction based on the energy criterion showed a good agreement with the experimental results.

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The bending properties of sandwich composite beams under static and cyclic loadings were investigated. The sandwich beam consists of hard urethane foam core and GFRP surface plates. Four-point bending tests were conducted to examine the effects of facing plate thickness and core rigidity on the flexural properties under static and cyclic loadings. The experimental results reveal that : (1) The bending stiffness and strength of the sandwich beams increase with increasing the facing plates. The effect of stiffness of core on the bending stiffness of the beams is small. (2) The final fracture of the beams occurs due to compressive failure of the facing plates although the tensile strain of the facing plates at failure is greater than that of the compressive side facing plates. (3) The fatigue bending strength for the sandwich beams having thinner facing plates is high when the fatigue bending strength is given by the normalized strength using the static bending strength. (4) The fatigue failure of the beams occurs due to fracture of compressive side facing plates in compression at low cyclic fatigue while the tensile failure of tensile side facing plates leads the final failure of the beams at high cycle fatigue.

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Fatigue tests under axial loading with tensile mean stresses were carried out on the specimens of 0.20% and 0.45% carbon annealed steels. The main results are summarized as follows : (1) The S-N curves under various mean stresses are almost the same in the range of finite lives, provided that the true stress amplitude is used by considering the constricted cross-sectional area. This is due to the fact that plastic deformation is easier to occur in the layer of specimen surface than in the inside of specimen. (2) The constriction of specimen during fatigue tests occurs when the maximum stress during stress cycling is higher than a definite value close to the yield stress. (3) The range where the small crack growth law is applicable was clarified in these materials.

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The objective of this study is to investigate the characteristics of fatigue crack growth in a fiber/metal laminate GLARE 3-5/4. This material consists of five 2024-T3 Al alloy thin sheets and four layers of a (0°/90°) glass/epoxy composite. Centrally notched specimens were fatigue tested under constant amplitude loading and crack length was measured using a DC potentialdrop method. The following conclusions were obtained : (1) The scatter in fatigue crack growth lives was a little larger than that of a 2024-T3 Al alloy. (2) The relationship between crack growth rate, da/dN, versus stress intensity factor range, ΔK, obtained on the assumption of a monolithic material was different from that of a single 2024-T3 Al alloy sampled from the GLARE and showed the maximum stress dependence. (3) The relationship between da/dN and ΔK_nn, the stress intensity factor range analyzed by Marissen on the basis of a fiber bridging effect, approximately agreed with that of a single 2024-T3 Al alloy specimen regardless of the maximum stress.

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The delamination crack growth behavior under iso-thermal and thermo-mechanical fatigue were investigated with unidirectional CF/epoxy laminates. Tests were conducted either in air or in water with double cantilever beam specimens. The crack growth tests were conducted under constant ΔK conditions. In air, the delamination crack growth rates for the iso-thermal fatigue tests were higher for higher temperature, and the crack growth rates for the thermo-mechanical fatigue tests were lower than those for the iso-thermal fatigue tests. The crack growth rates for the in-phase thermo-mechanical tests were lower than those for the out-of-phase thermo-mechanical tests. In water, the crack growth rates for the iso-thermal fatigue tests were higher for higher temperature under high stress ratio. The rates, however, were not monotonically changed with test temperature under low stress ratio. The rates for the themo-mechanical fatigue test were almost the same value as those for the iso-thermal fatigue test whose test temperature was equal to that at the maximum load for the themo-mechanical fatigue test. The most remarkable difference in the growth behavior between present material and the material employed for the 1st report appeared in the thermo mechanical fatigue crack growth tests in air

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The loading frequency dependence of fatigue crack growth in the near-threshold region were investigated using constant K_max test method at 550°C. Crack growth rates at f=30 and 3 Hz in different specimens were compared. To realize intra-specimen comparisons, loading frequency was changed from 30 Hz to 3 Hz and 30 Hz. After the increase of K_max in the threshold condition, crack grew even in the region below the threshold value determined using conventional constant R test method at every loading frequency. By comparing crack growth behaviors at different loading frequencies. it was found that the loading frequency gave some influences on threshold behavior and crack growth behavior in the region below the conventional threshold value.

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The fatigue crack growth behavior of A 533 B steel which was subjected to PWHT and stepcooling heat treatments was examined in a simulated BWR water environment and in air. The test variables investigated included thermal aging effect, frequency variation over the range 0.05 to 0.5 Hz, and R-ratios of 0.1 and 0.5. The physical and metallographic examinations were carried out using transmission and scanning electron microscopes, and Auger spectroscopy. The results show that the thermal aging such as the step-cooling has no noticeable effect on the fatigue crack growth behavior both in air and 288°C water environment. The crack growth rate in 288°C water environment is accelerated when frequency decreased and stress ratio increased. The acceleration of the crack growth rate may be due to occurrence of quasi cleavage associated with hydrogen embrittlement.

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Hard shot-peening (HSP) treatment was very successful for the improvement of the high cycle fatigue strength of SUS 316 L steel. However, the surface roughness by the HSP treatment was one of the dropping factors on the fatigue strength. In order to separate surface roughness effects from effects of compressive residual stress and strain hardening by the HSP treatment, the HSP-treated SUS 316 L was annealed in the vacuum to remove residual stress and recrystallization in hardened layer. The rotating bending fatigue tests for the annealed specimen were carried out under water cooling condition. The fatigue limit of annealed SUS 316 L was about 60 MPa lower than that of non-peened specimen which was about 200 MPa. To simulate the actual surface roughness, fatigue tests for the single notch specimens and small drilled holes specimens were carried out. As a result, the surface roughness effects by the HSP treatment were not consistent with the √(area) parameter model. The effects were explained by considering the stress concentration factor.

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The fatigue properties of austenitic stainless steels with different Cr/Ni equivalent values have been investigated in the high-cycles region using Ono-type rotating bending fatigue testing machine. The materials used in this test were three kinds of representative austenitic stainless steels, i. e. typical austenitic stainless steel, SUS304 and nitrogen-contained SUS304 (SUS304 N and YUS170). The main results obtained in this test are as follows ; (1) Though each material has the different δ-ferrite value according to Ni/Cr equivalent value, there are no relation between δ-ferrite value and fatigue limit. (2) The fatigue cracks do not necessarily initiate at the segregated portion of chemical content. (3) Considering Ni/Cr equivalent, the austenitic structure in YUS 170 is more stable than those in SUS 304 and SUS 304 N. Therefore, the increase of Micro-Vickers hardness due to deformation induced martensite transformation in YUS170 is lower than those in SUS 304 and SUS 304 N. (4) The lower fatigue strength, the larger the crack tip opening displacement (CTOD) of each material which has same fatigue life.

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The effects of small artificial defects on the fatigue limit of an annealed carbon steel have been investigated in the temperature range of 20°C to 450°C. The experimental results have been compared with those predicted by Murakami's √(area) model. Small drilling holes were used as artificial defects. The diameters of the holes were 0.1, 0.2 and 0.3 mm, respectively and their depths were almost the same as the diameter. The fatigue limits of the drilled specimens as well as the smooth specimens showed a sharp peak caused by dynamic strain aging near 350°C. Vickers hardness, HV_s, necessary for the application of the √(area) model was measured in the same temperature range as the fatigue tests. The Vickers hardness, HV_s, did not show such a sharp peak as the fatigue limit near 350°C. The fatigue limits obtained from the fatigue tests agreed with those predicted by the model within a scatter band of ±10% at 20°C and 250°C. The experimental values, however, were larger than the predictions at 350°C and 450°C. At 350°C, the deviation was large and its degree became about 35%. The results were attributed to a much greater effect of dynamic strain aging for the fatigue limit than for the hardness. When the hardness, HV_c, measured after fatigue loading was applied to the model, the deviation was decreased to 18%. Thereafter modified hardness, HV_f, obtained by multiplying fatigue limit ratio, R_f, to the hardness, HV_s, was applied to the model, where R_f is the ratio of high temperature fatigue limit to room temperature fatigue limit. Most of the results were in the scatter band of ±10% from the predicted value.

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Fracture mechanisms and residual strength of fatigue-loaded FRPP with notch are studied by means of acoustic emission technique. The maximum AE cumulative event count and the maximum total AE energy increase in the ratio of number of cycles N to number of cycles to failure N_f, N/N_f, and the load at AE initiation and the loads at change of damage mechanisms decrease similarly to the maximum load, although the degree of damage is varied by the stress amplitude. In the case of small fatigue-damage the many resin crackings occur, but in the case of large fatigue damage the damage mode changes from the fiber debonding to the fiber breaking. The microfractographs prove the estimation by AE frequency analysis. It is found that the residual strength of fatigue-damaged specimen is determined by the load ratios P_i/P_{i (N)} and P_b/P <b (N)>, where the suffix (N) shows the nondamaged specimen, but the reliability of P_i/P_{i (N)} is poorer than that of P_b/P_{b (N)}.

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In this study, plastic-strain-controlled low cycle fatigue tests were carried out using cylindrical specimens of three kinds of spherodial graphite cast iron (ferritic ; FDI, pearlitic : PDI, and austempered ; ADI). In order to specify the kind of defect in fracture origin, a fracture section was observed by using SEM. As a result, the fracture starts at microshrinkages that exist on the neighboring surface in these materials. The length of microshrinkages projected on the surface ranges from 100 to 800 μm. Also, there is no precise relationship between the fatigue life and the observed shape of microshrinkages. In the specimen with a small blind hole having 0.4 mm diameter (the depth of it equals the diameter), the fracture starts at the hole. However, in the specimen with a small blind hole of 0.2 mm diameter, it starts at microshrinkages.

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In this study, a three dimensional elastic problem for an inhomogeneous medium whose shear modulus G increases with coordinate variable z according to relation G (z)=G₀ (1+z/a)^m (G₀, α and m are constants) is developed. In our previous paper, we derived the fundamental equations system for such inhomogeneous medium by using three kinds of displacement functions and applied them to determining the elastic stress distribution in a semi-infinite body subject to an arbitrary shaped distributed load (not necessarily axisymmetric) on its plane surface. In this paper, we apply these fundamental equations system to the inhomogeneous semi-infinite body whose plane surface is penetrated slowly by a rigid cylindrical punch of arbitrary shape. As an example, we consider the case where the inclined flat-ended cylinder indents the plane surface of the inhomogeneous semi-infinite body. Numerical calculations are carried out for several cases taking into account the variation in inhomogeneous elastic properties, and the numerical results for displacements, stress and stress intensity factor at the edge of the rigid punch are shown graphically.

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In this study, a plate subjected to a suddenly applied surface force which travels constant velocity on the surface is analyzed. The transformed solutions in the Laplace and Fourier domains include the function of Rayleigh-Lamb frequency equation. Their solutions are expanded into infinite series form, and then the inverse transforms are carried out for the each term of the series using the Cagniard-deHoop method. The exact transient closed-form solutions in the time domain are also expressed in infinite series form and their each term represents physical transient wave. It is shown that the amplitude ratios of reflection of P wave and SV wave are same for the cases of harmonic waves. The numerical results of velocity fields are shown by graphical representation.

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The fundamental solutions have been obtained for a fluid-saturated, elastically isotropic, porous, infinite solid with transversely isotropic permeability under an instantaneous fluid point source and instantaneous point forces acting in mutually orthogonal directions. The solutions include those for the case of zero permeability in one direction as a limiting case. These solutions are intended to be used to derive the integral equations for a plane crack of arbitrary shape ; these equations in turn will be implanted in a hydraulic fracturing simulator for the gas/oil production.

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In this research, the behaviour of crack-rate sensitive brittle materials in three point bending tests with an abrupt change of loading velocity was studied. The experiments using crack stabilizer and the numerical simulations taking account of crack-rate effect on fracture toughness were performed for two types of tests, i.e. incremental (or decremental) and relaxation tests. After a change of loading velocity from V₀ to V₁, a transition range on the load-deflection curve was observed. In the relaxation tests, the load decreases gradually with time. However, the stable crack extension still continued even after the loading velocity equalled zero. These results observed in incremental and relaxation tests were well simulated by the numerical simulations. It was also found that these tests were quite useful to determine the crack-rate sensitivity parameter of the test materials.

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Cavitation erosion mechanisms were studied through the observation of erosion particles for carbon steels. In the initial period and the incubation period, many small sharply-edged particles were produced by single impact loads. In the accumulation period and the steady-state period, large striated particles were observed due to cyclic loads. The volume fraction of fatigue fracture is 70% to 80% in these periods incubation pure copper and pure aluminum. The exponent of the crack growth rate observed on the cross section of the eroded specimen is almost the same as that obtained from a regular fatigue test. The fatigue crack growth rate for many metals depends on a reciprocal of the square of Young's modulus (1/E²). The particles fall off from the tip of uneven surface. The maximum diameter of erosion particle decreases inversely to the square root of Vickers hardness (1/HV^1/2), thus the volume is proportional to 1/HV^3/2. Therefore, the volume loss rate in the steadystate period corresponds well with the 1/(HV^3/2·E²). It was concluded that cavitation erosion can be evaluated in the terms of the material hardness and the fatigue crack growth.

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Two types of electromagnetic acoustic transducers (EMATs), both for longitudinal wave in steel wire, are developed. In inspection of steel wires throughout a long range, ultrasonic wave will be an effective tool. The EMAT, which consists of a coil surrounding the wire and an electromagnet, enables us to generate and detect the longitudinal wave at an arbitrary position of the wire, and seems to be suitable for this purpose. However, there are two problems to be solved, both can be attributed to the characteristic of the EMAT. First, the magnetostriction of the wire limits the saturation amplitude of the generated wave, though it is required to be high to improve the signal to noise ratio. We develop a multiple EMAT, which effectively amplifies the signal by overlapping the waves excited by some equivalent coils. The other problem is that the EMAT launches the longitudinal wave symmetrically in two directions. To estimate the position of the flaw, the measurement should be done from at least two different locations of the EMAT. We also produce a unidirectional EMAT with two equivalent coils. One of the two directional waves excited by one coil is canceled by antiphase wave from the other coil. Combination of these two techniques is proved to be the solution for the above two intrinsic problems of the EMAT.

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It is well known that bone has a capability to adapt to usual mechanical environment and to reconstruct functionally its structure and geometry. This phenomenon is called as the adaptive bone remodeling. One of the most important mechanical factor of the remodeling is the stress. To generate the bone remodeling, the stress should remain to stimulate the osteocyte in the relative long period. Thus stress will be a kind of residual stress. To verify this assumption, it is a great significance to measure the residual stress is intact bone tissue. Bone has extremely anisotropic structure which consists of hydroxyapatite crystals. In this work, a method to measure the anisotropic residual stress in compact bone is proposed using the polychromatic X-ray diffraction method. The interplanar spacing of the hydroxyapatite in the bone can be measured by using the polychromatic X-rays diffraction. The ratio of atomic interplanar distance of a strained to a nonstrained specimen was defined as the lattice strain. The biaxial residual stress could be calculated from the lattice strains measured at three directions. The compact bone of bovine diaphysis was used as a specimen. To observe the difference of region, the specimen was taken from the middle region of diaphysis divided into four parts : anterior, posterior, medial, lateral, at each bone axial and circumferential directions. As a result, it was confirmed that the residual stress in the bone could be evaluated nondestructively by this method. The tensile residual stress were found in the bone axial direction of the bovine femoral bone.

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