This paper describes a fast boundary integral equation method (BIEM) for elastodynamic problems in 2 D in time domain for solving very large scale initial-boundary value problems which cannot be analyzed with the conventional BIEM within an affordable amount of time. At first, we derive a plane wave expansion of the fundamental solution of elastodynamic problems. This expansion formula enables us to construct a fast algorithm for evaluating the layer potentials in BIE which uses the multilevel plane wave time domain (PWTD) algorithm, that was originally developed by A. Ergin and M. Lu et al, in scalar wave problems. Finally, a fast solution method is obtained with the help of this algorithm and an Iterative solver for linear algebraic equations. Some numerical examples show that the proposed method solves large scale problems faster than the conventional one.

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An effective optimization technique for cathodic protection design is developed. To cope with the large amount of memory and calculation, the fast multipole boundary element method (FMBEM) is applied. To achieve an effective optimization, the initial values of the design variables, i, e., the location and current of each electrode, are determined by solving an inverse problem. In the inverse problem both of the potential and the current density on the metal surfaces to be protected are given as the ideal values, i.e., the protection potential and its corresponding current density. The inverse problem is solved effectively by using the FMBEM. Using thus obtained initial values, the optimization problem is solved by the symplex method. A couple of example problems are solved to demonstrate the effectiveness and usefulness of the present method.

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In the analysis of inverse problems in various fields, it seems that a priori assumptions for the solution is required. This requirement causes many inconveniences on the analysis. We have developed a new analysis scheme for the inverse problems by Introducing the discrete integral method utilizing the delta function. In this report, the new scheme is applied to the one dimensional inverse problems, Namely, a scheme for solving the inverse problem on identification of external loads applied on a beam is developed. It is proved through many examples that the present scheme will give accurate solutions without any assumptions.

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In order to establish the assessment method of creep damage for high temperature piping components made of modified 9Cr-1Mo steel with seam weld, subjected to internal pressure, the internal pressure creep tests and FEM stress analysis were done for cylinders with seam weld. In internal pressure creep tests, the creep rupture occurred at fine grained heat affected zone (F. G. HAZ), caused by cracking originated from the formation of voids. The correlation between void area fraction and creep damage was obtained. The morphology of voids were quite similar to that observed in welded joint specimens in uni-axial creep tests. Stress distribution of seam weld cylinder under internal pressure creep showed the higher circumferential stresses in F. G. HAZ where creep rupture occurred. The distribution of circumferential stress and creep damage calculated by using circumferential stress along specimen thickness were quite similar to that of void area fraction in internal pressure creep test. The creep damage in seam weld pipe under internal pressure creep could be estimated by the observation of void area fraction in F. G. HAZ.

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The displacement rate-controlled tensile tests were performed for smooth and circumferentially notched specimens of the sintered silicon nitride ceramics in argon-gas atmosphere at 1300°C, and then the axial load-displacement response was measured. It was shown from the tests that inelastic deformation was greatly dependent on displacement rate and easier to generate at the lower displacement rate. The constitutive equation was constructed on the basis of tensile stress-strain curves in the smooth specimen. Then Inelastic FEM analysis was performed for the smooth and notched specimens, using this equation. The calculated load-displacement responses quantitatively agreed quite well with those in the smooth and notched specimens, showing the validity of the proposed analysis. The development of the Inelastic deformation in loading process was shown from the calculation around the notch root.

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The deformation properties of TiNi shape memory alloy subjected to strain control and stress control were investigated experimentally. The results obtained are summarized as follows. (1) In the case of full loop, the stress-strain curves under stress-controlled condition are similar to those under strain-controlled condition with high strain rate. The overshoot and undershoot do not appear at the start points of the stress-induced martensitic transformation in these curves. (2) In the case of subloop under stress-controlled condition, temperature decreases and therefore strain increases owing to the martensitic transformation at the early stage in the unloading process. At the early stage in the reloading process, temperature increases and therefore strain decreases owing to the reverse transformation. (3) In the case of subloop under stress-controlled condition, the starting stresses of the martensitic transformation and the reverse transformation in the loading and unloading processes coincide with the transformation stresses under strain-controlled condition with low strain rate, respectively. (4) The deformation behaviors for subloop under stress-controlled condition are prescribed by the condition of progress of the martensitic transformation based on the transformation kinetics.

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B-C-N films have been synthesized by ion-beam-assisted deposition technique, in which boron and carbon were evaporated by electron beam and a mixed nitrogen and argon ion beam was simultaneously irradiated onto silicon (100) substrates. The ratio of argon ions to nitrogen ions was varied by the flow rate ratio of Ar and N₂ gases fed into the ion source. In this experiment, the influence of the ratio on the mechanical properties and the microstructure were investigated. Nano-indentation studies showed the maximum hardness up to 23 GPa at the gas ratio of 25-50%. The films prepared under the appropriate conditions indicated low friction coefficient of 0.04-0.08 against a sapphire pin and excellent wear resistance. The existence of cubic-phase B-C-N crystal-line in the film which has been predicted as one of new hard materials was revealed by transmission electron microscopy image. It was concluded that the superior mechanical properties prepared at the optimum gas ratio could be attributed to the appearance of the new cubic phase.

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The relation of the microstructure, the dynamic viscoelasticity, the molecule orientation and the micro hardness of the PP/LCP blends to the tensile property have been examined by rolling tests. The result shows that : (1) With the increase in the rolling ratio, (1) the LCP phase of reinforcement is delayed and the distribution is improved. (2) The specimens is softened as the E' and the section hardness decrease. (3) The distribution of hardness and the molecule orientation in all specimen sections become more uniform. (2) The rolling process has improved the material property of brittle blends and their ductile property rises drastically. Especially, under the high rolling ratios such as 60% the strength and the stretch of the material have been improves greatly. (3) Thus, it is considered that the rolling processing may be an effective way to improve the microstructure, phases interface bond strength and ductile property of composite material.

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Effects of the rolling ratio, the stress amplitude and the test temperature on the fatigue property of the rolled PP/LCP blends have been examined from the variation of dynamic viscoelasticity factor during the fatigue process. The results show that : (1) Under a low rolling ratio (within 40%), the specimen was softened and easily to generate heat. Therefore, it ruptures for the ductile fracture earlier than the unrolled specimen. (2) For the 60% rolled specimen, with the increase of stress amplitude level the E' decrease while the tan δ, Ts, ΔL, Ld increase. The ductile fracture tendency became more evident. But, the specimens had not ruptured under all stress level and test temperature. It shows an excellent fatigue resistance property. (3) The resistance to fatigue becomes better as the test temperature decreases. Especially, it shows a high ductile, high strength and high fatigue resistance even under -10°C when the blends material, which lost the ductile property even under the room temperature, is pressed at 60%.

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Interlaminar fracture behavior of hybrid composites with non-woven carbon tissue is investigated under a Mode I loading condition with a DCB specimen. Hybrid composites are made by inserting non-woven tissue between prepreg layers. Two kinds of specimens are prepared from [0]₂₄ and [0₁₂/ 0₁₂]. Here the symbol "/" means that non-woven carbon tissue is located at a 0/0 mid-plane of the specimen. An initial interlaminar crack is introduced to a mid-plane of the specimen. Interlaminar fracture toughness (G_IC) of hybrid composites is compared with that of CFRP. G_IC of hybrid composites is almost dependent on only that of matrix resin. The fracture surfaces of the specimens are observed with an optical microscope and SEM, and the failure mechanism is discussed.

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Mechanical behavior characteristics of hybrid composites with non-woven carbon tissue are investigated under static tensile loading. This hybrid laminate consists of unidirectional prepreg and non-woven carbon tissue, made by inserting non-woven carbon tissue between prepreg layers. Static tensile test of CFRP and hybrid laminates are carried out. Chord shear modulus and 0.2%-offset shear strength of a CFRP laminates are obtained and compared with those of the hybrid laminates. The hybrid laminates, seem to be effective to improve the tensile characteristics. The fracture surfaces of the specimens are observed with SEM and an optical microscope, and the failure mechanism is discussed.

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The stress and displacement fields near the bonding edge, sharp notch, and contact edge show singularity behaviors, so methods of evaluating the strength of these points using maximum stresses calculated by a numerical stress analysis, such as the finite element method, are generally not valid. We have previously presented a new method of evaluating the strengh of these singular points using two stress singularity parameters H and λ. The difficulty with this method was in obtaining the critical value of the intensity of the stress singularity parameter Hc for each order of stress singularity λ. We therefore present in this paper methods of formularizing Hc by λ based on typical strength parameters such as the fatigue limit σ_w0 and the threshold stress Intensity factor range ΔK_th. These critical value Hc(λ) agreed well with the experimental results. Using these easily obtained formularized critical value Hc(λ), we can estimate the fretting fatigue crack initiation criteria for each contact edge angle, and thus optimize the contact edge geometry. Finally, we discuss the development of these strength criteria in terms of stress singularity fields for general stress concentration fields.

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This paper deals with the deformation and damage of CFRP cross-ply laminates under off-axis tension and develops a non-linear lamination theory. Off-axis tensile tests were carried out on five kinds of CFRP cross-ply laminates which were different in stacking lay-up. On the laminates under off-axis tension, the stress-strain response shows the non-linear deformation, while the ply-cracking damage is not remarkable except for the specimen with large fracture strain. Therefore, It is concluded that the non-linear deformation of the laminates under off-axis tension is mainly attributed to the non-linear deformation of the matrix resin. In order to describe the deformation of the laminates, a non-linear lamination theory is developed. An incremental constitutive relation of the unidirectional composite containing elastic long fibers in the elastic-plastic matrix is derived based on Eshelby's equivalent inclusion method and Mori-Tanaka mean field concept. Then, this constitutive relation is introduced Into the classical lamination theory. Numerical results by the present theory for off-axis tension of the CFRP unidirectional and cross-ply laminates well described the experimental stress-strain relations.

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Damage accumulation In GFRP during tension/torsion biaxial fatigue was studied. Under uniaxial tension and biaxial loadings, longitudinal fibers continuously break from the first cycle to the final failure of the material at low cyclic fatigue. In the case of high cyclic fatigue, a few longitudinal fibers break during a first few cycles. Few longitudinal fibers fail after the first stage of fatigue. Primary types of internal damage at the second stage are debonding and cracking in the matrix. After such damage grows to some extent, longitudinal fibers resume to fail. This fiber breakage leads to the final fracture of the material. In the case that a combined load is applied, longitudinal fibers are not aligned parallel to normal stress due to shear deformation. These misalignment and shear deformation cause a peeling stress at the interface between fibers and matrix. As a result of this peeling stress, debonds propagate more rapidly under biaxial loading than under uniaxial tension or pure shear loading. This mechanism could be a reason for shorter fatigue life under combined loading than that under uniaxial tension and pure shear loadings.

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The surface SH waves technique has been used to evaluate the fatigue cracks at the surface of mild steel specimens. By adjusting incident angle of SH wave transducer, surface SH waves passing through the surface region of materials are received. In this study, the diffraction of surface SH waves received by double-probe technique was used. Firstly, the specimens introduced surface slit were inspected. With the results that the amplitude decreased and the propagation time increased with the slit depth. Secondly, the shapes of the fatigue cracks, which initiated at a small drill hole by rotating-bending fatigue, were evaluated with the difference between the propagation time of the inspected plate with crack. Obtained results showed that the evaluated values of crack length and crack depth were good agreement with the measured values. Furthermore, this technique was applied to evaluating the crack growth behavior.

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Static and fatigue crack propagation properties of epoxy adhesives under Mode I, Mode II and their Mixed Mode loading were investigated. Three types of specimens were used to examine the effect of the mixed mode ratio on the static and fatigue criteria ; Double cantilever beam (DCB) for Mode I, Tapered End Notched Flexure (TENF) for Mode II and Mixed Mode Bending (MMB) specimens. Two types of epoxy adhesives (unmodified and toughened with sub-micron rubber particles) were tested. The static test results revealed that the fracture toughness of unmodified and toughened epoxy adhesives (evaluated by the total energy release ratio G_t= G_I+ G_II) changed with respect to a mixed mode ratio (Mode I /Mode II). The fatigue test also revealed that the crack grows characteristics in the epoxy adhesives (such as a da/dN-ΔG_t, relation) also changed with respect to a mixed mode ratlo.

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Spheroidal graphite cast iron has many graphite nodules and other casting defects such as microshrinkage cavities in the structure. These small defects cause reduction and scatter in the fatigue strength. In this study, rotating bending, reversed torsion and in-phase combined axial/torsional fatigue tests were carried out on smooth round-bars of FCD 400, FCD 600 and FCD 700. The fatigue limit was determined by the threshold condition for propagation of a small mode I crack emanating from small defects. Using both the multiaxial fatigue fracture criterion derived based on this observational result and the √(area) parameter model, a unified method for predicting the lower bound of fatigue limit of spheroidal graphite cast irons subjected to combined loading was proposed. The predicted and experimental results agreed well.

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Geothermal energy is one of the most environment-conscious resources among the natural resources. Recently, the development of a supercritical geothermal system has been proposed to enhance the geothermal heat extraction. In order to design the supercritical geothermal reservoir whose temperature and pressure conditions exceed the critical point of water, the formation behavior of the geothermal reservoir under the great depth condition has to be examined. In this study, we develop a new numerical analysis code for analyzing the hydraulic fracturing behavior in deep-seated rock mass. This code consists of two parts : "flow analysis" which computes the pressure distribution in the induced crack, and "crack propagation analysis". The former is based on FDM. The later is based on FEM with embedded crack element. In the "crack propagation analysis", the mixed-mode fracture behavior with process zone formation is modeled. A shear dilation is accounted for in the fracture model. The numerical result shows that the crack growth behavior, i.e. the mode of crack propagation changes from mode I to mode II as the depth increases. Under a typical tectonic stress condition, the crack growth mode is dominated by the mode I component above 4-5 km depth, whereas the influence of mode II component increases with increasing the depth. This result may suggest that the current target of supercritical geothermal reservoirs may be formed mainly under the mode I fracture.

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In this paper we analyze the crack arrest depth for an inner-surface circumferential crack in a finite-length cylinder under cyclic thermal shock. The edges of the cylinder were rotation-restrained and the inside of the cylinder was cooled from uniform temperature distribution. The effects of structural parameters and the heat transfer conditions on the maximum transient stress intensity factor were investigated with the previously developed systematic evaluation methods. Then, assuming the Paris law and a tentative value of threshold stress intensity range ΔK_th, we evaluated the crack depth for crack arrest under cyclic thermal shock. Finally, we developed a map to find the crack arrest depth for a cylinder with mean radius to wall thickness ratio R_m/ W= 1 and a specific length H under various heat transfer conditions. From this map, we can predict that when the heat transfer coefficient and/or initial wall-coolant temperature differences are large enough, the non-dimensional crack arrest depth saturates at a specific value and is no longer affected by material properties of the cylinder.

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It is known that the stress singularity at a corner point where the front of 3D cracks intersect free surface is depend on Poisson's ratio and different from the one of ordinary crack. In this paper, a singular integral equation method is applied to calculate the stress intensity factor along crack front of a 3-D semi-elliptical surface crack in a semi-infinite body under mixed mode loading. The body force method is used to formulate the problem as a system of singular integral equations with singularities of the form r^-3 using the stress field induced by a force doublet in a semi-infinite body as fundamental solution. In the numerical calculation, unknown body force densities are approximated by using fundamental density functions and polynomials. The results show that the present method yields smooth variations of mixed modes stress intensity factors along the crack front accurately. Distributions of stress intensity factors are indicated in tables and figures with varying the elliptical shape and Poisson's ratio.

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This paper studies the effect of vacuum on the creep rupture time of SUS 316 unnotched and notched round bar specimens. Creep and creep rupture tests were carried out using three types of notched specimens in air and vacuum at 873 K. Creep rupture times of the unnotched and notched specimens in vacuum were shorter than those in air. The reduction of rupture time due to the vacuum was smaller In notched specimens compared with unnotched specimens. The rupture time ratio, tr (notched)/tr (unnotched), in vacuum was larger than that in air. The environmental rupture time ratio, tr (air)/tr (vacuum), decreased with increasing the elastic stress concentration factor. The effect of vacuum was attributed to the crack initiation and propagation periods.

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