The extended finite element method (X-FEM) is applied to three-dimensional elastic-plastic crack problems. The developed X-FEM code uses 8-node hexahedral finite elements and the level set method to model a planar crack with various geometry independently of the finite element and can perform static analysis considering the elastic-plastic constitutive equations and evaluate the J-integral at the crack front by the domain integral method. Moreover the ductile crack propagation simulation can be performed by executing the elastic-plastic analysis code successively. In this paper the outline of the developed system and results for semi-elliptical planar crack in a plate is shown.

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Conventional FEM is continually used for the flaw evaluation of pipe structures to investigate the fitness-for-service for power plant components, however, it is generally time consuming to make a model of specific crack configuration. The consideration of a propagating surface-crack is further accentuated since the crack propagation behavior along the crack front is implicitly affected by the distribution of the crack driving force along the crack front The authors developed a system to conduct crack propagation analysis by use of the three-dimensional elastic-plastic X-FEM. It can realize the simultaneous calculation of the J-integral and the consequent ductile crack propagation. In this presentation, some typical results of the application of the developed system to ductile crack propagation for circumferentially surface cracks in pipe structures are presented.

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JSME rules on fitness-for-service for nuclear power plants (Ver. 2004) gives Z-factors for circumferentially cracked austenitic stainless steel and ferritic steel pipe as one of elastic plastic fracture mechanics evaluation method. The technical basis of Z-factor for thermal aged austenitic stainless pipe was given by the previously published paper, but necessary and sufficient condition was not described to perform the trace calculation for derivation of Z-factor's equation. This paper gives the Z-factor's calculation conditions of thermal aged SAW and duplex stainless steel and shows the result of the trace calculation result

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The Japan Society of Mechanical Engineers provides the rules on fitness-for-service for nuclear power plants. The critical crack sizes in the acceptance criteria in the rules are determined through the evaluation of fracture loads. For austenitic stainless steels pipes with cracks, fracture loads of base metal and welded material can be predicted as the net-section collapse load and elastic-plastic fracture load, respectively, and the procedure to evaluate the fracture loads is addressed using the concept of Z-factor. hi this paper, the adequacy of the Z-factor provided in the present rules was investigated by comparing with the three-dimensional elastic-plastic finite element analysis results.

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Rules on Fitness-for-Service for nuclear power plants in JSME Code define allowable flaw depth for Class 1 vessels and piping in the Acceptance Standards. When a detected flaw is a subsurface flaw located near the component surface, the subsurface flaw should be transformed into the surface flaw. However, the inconsistency of allowable flaw depth could be seen at the transformation of subsurface flaw to the surface flaw. For the proposal of new revised Acceptance Standards, which keep a consistency of allowable flaw depth at the transformation, the effect of distance of subsurface flaw from the component surface on structural integrity of the flawed component should be evaluated. In this paper, the stress intensity factors of the subsurface flaws near the component surface were calculated to discuss the revised allowable flaw depth of subsurface flaw in Acceptance Standards. Since the estimations of stress intensity factors indicated that the stress intensity factors of subsurface flaws are not sensitive with distance from the component surface, the new revised Acceptance Standards for subsurface flaws should be only considered from the viewpoint of the consistency of allowable flaw depth at the transformation of subsurface into surface flaw.

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This study presents evaluation method of crack growth rates and behaviors for semi-elliptical surface cracks in plates subjected to arbitrarily stress distributions. In order to calculate stress intensity factors, we developed influence coefficients based on the influence function method used finite element method. We enable to calculate stress intensity factors directly from arbitrarily stress distributions evaluated by finite element method, because of arbitrarily stress distributions as weld residual stress on the crack surface are difficult to approximate by polynomial equations. As a result of comparison between our calculations and the Newman-Raju formula, both stress intensity factors agreed well. From calculated stress intensity factors, we evaluated asymmetrical crack growth rates and behaviors in a short time.

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Stress Corrosion Cracking (SCC) has been observed as circumferential multiple flaws in weld heat-affected zone of primary loop recirculation system piping and core shroud made of low carbon stainless steel. In the Japan Society of Mechanical Engineers code, Rules on Fitness-for-Service for Nuclear Power Plants, there is no fracture assessment of piping with multiple flaws which are not applied to combination rule criteria. Through fracture test of piping with circumferential two flaws in weld heat-affected zone, the limit load estimation method was evaluated for fracture assessment of stainless steel piping.

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One of the mechanisms which clarify the strain concentration at discontinuities in structures is the concept of elastic follow-up. In order to evaluate quantitatively the strain concentration, that concept was evolved into the method with the Stress Redistribution Locus (SRL) which is unique to each structure. On this study, the numerical simulations on the "Pipe Model" which takes after actual pipes should be run and it is examined on this model how strain is concentrated inside the pipe. According to that examination, a hypothesis is made that the main factor which determines the shape of SRL is the size ratio of the plastic region to the elastic region in structure. Based on this hypothesis, the "Plastic Region Fixed Model", a pipe-like model in which the size ratio is tied up, was recognized. As a result of simulations on that model, it could be confirmed that the hypothesis is appropriate.

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Stress Corrosion Cracking (SCC) crack growth rate (CGR) curve for nickel-base alloy weld metal in Boiling Water Reactor (BWR) environments was proposed. The curve can serve to evaluate CGR dependence on electrochemical corrosion potential (ECP), from normal water chemistry (NWC) to hydrogen water chemistry (HWC).

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The SCC crack propagation is predicted by using the proposed SCC crack growth rate reference curve that reflects the latest data for the crack in the block weld in the CRD stub tube. It was shown that the SCC crack propagation of a real plant was almost appreciable. The SCC crack propagation of HWC is more gradual than that of NWC. Therefore, it was shown to make the first conducting of the examination time by VT-2 provided for by the Fitness-for-Service longer.

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The Stress Corrosion Cracking has been observed in a component of low carbon austenitic stainless steel in the BWRs. It is necessary to examine various factors on the SCC crack propagation for the operation and maintenance and the reliability securing of the aged plant. In this study, the effect of the cyclic load that causes it for SCC crack propagation in simulated BWR environment is examined by using the CT specimen of cold-rolled stainless steels (SUS316L). As a result of the examination, the retardation phenomenon was observed as for the SCC crack immediately after the cyclic load was received.

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We are studying incorporating a fracture evaluation method for Alloy 600 into the JSME Fit-for-Service Codes. A PWSCC (Primary Water Stress Corrosion Cracking) propagation diagram has been proposed by JNESS NiSCC Project. The PWSCC depths that occurred in the dissimilar metal weld of the actual steam generators' nozzles and so on and those that consist of PWSCC initiation and propagation analyses are compared to incorporate the proposed diagram into the JSME Fit-for-Service Codes.

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SCC growth tests on the specimens machined out from SMAW and GTAW weld joints of low carbon type 316L stainless steel were conducted in simulated BWR coolant condition to clarify effect of loading direction on SCC growth behavior near weld fusion line. Results suggested that SCC in the base metal tends to propagate to avoid the weld metal and the relationship between dendrite orientation and loading direction affects SCC propagation into weld metal.

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In this study, water absorption and flexural strength properties of carbon fiber reinforced plastics (CFRP) were examined. The properties of epoxy resin were also examined. Mass gains were measured after immersion in a distilled water under RT(Room Temperature), 50℃, 70℃ and 90℃ conditions. Static flexural tests were conducted after immersion for 180 days. As a result, following conclusions were obtained. Mass gain of CFRP and epoxy resin increased with an increase of water temperature. The reason of this phenomenon was the cracks occurred in CFRP and epoxy resin when CFRP and epoxy resin were immersed in a distilled water at 90℃. The flexural strength of CFRP and epoxy resin did not decrease over 60.8%, 78.5% in a distilled water for 180 days. When CFRP and epoxy resin were immersed in a distilled water over 120days at high temperature, strength did not recover over 43.8%, 70.8% by drying. The reasons were the cracks occurred in matrix.

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Fiber/matrix interfacial crack propagation behavior was investigated by using a real-size model composite. The model composite specimen used in the present study consists of two fibers bonded by matrix resin, and an interfacial crack can propagate without resin fracture in this specimen. Model composite specimens with an initial crack were successfully fabricated from the silane-treated glass fibers of about 10〜13 μm in diameter and vinylester resin. The mode II crack propagation tests were carried out by the developed micromaterial testing system. The average value of interfacial fracture toughness obtained from the present model composite specimens was much smaller than that obtained from similar model composites of fibers with 350 μm in diameter. This result suggests that the contribution of resin plastic work to energy dissipation becomes smaller for the present model composite specimen because of small fiber distance.

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In recent years, a large number of CFRP members are used in aircrafts for weight saving. One of the major fastening methods for the CFRP members is bolted joint. CFRP bolted joints, although, have a problem that the cracks or plastic deformation are occurred at the bearing surface of CFRP members even by the tightening with low fastening force. As a result, CFRP failures around bolt holes occur by stress concentration, and strength of a CFRP joint becomes decreased. In order to improve this problem, configurations of the washers are changed in this study to relax stress concentration, and thin sheet with high friction coefficient is sandwiched between CFRP members to improve the friction force. In the validation testing, the failure strength of the proposal CFRP bolted joint become higher than normal CFRP bolted joints.

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The microscopic damage in filament-wound carbon fiber reinforced plastics (CFRP) laminated pipes with three different laminate thicknesses subjected to impact loading were investigated in the present study. The impact tests were conducted to investigate the effect of the laminate thickness on the damage progress using a drop-weight testing device. The impact loading caused fiber damages and delamination in the all types of composite pipes. Delamination was suppressed in the thicker specimen. As a result, the absorbed energy became smaller with increasing laminate thickness. Internal pressure test were also conducted on the specimens after impact tests. The residual strength was larger in the composite pipes with thicker CFRP layers. These results prove that the composite pipes with thicker CFRP layers are superior in the impact resistance.

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Glass/epoxy interfacial tensile strength is investigated by the cruciform specimen method. A cruciform specimen which has large width only around fiber embedded in transverse direction can potentially prevent the stress singularity problem. The cruciform specimen geometry is first discussed by means of finite element analysis considering experimental conditions. Transverse tensile test is conducted and interfacial debonding which initiates at the middle of specimen not at edge is observed using the cruciform specimens. The interfacial tensile strength can be obtained by the value of stress concentration factor at interface times specimen stress. The location at which the debonding initiates is discussed and the validity of the evaluation method in this study is verified on an assumption that interfacial tensile strength is as high as or lower than interfacial shear strength.v

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The green composite has attracted special interesting recently. From the viewpoint of the effective utilization of waste wood, we proposed the composite composed of woodchips as the matrix material, bamboo fibers as the reinforced fiber and the biodegradable resin as the adhesive. The composite was formed a mixture of those materials into correct shape by press at the appropriate temperature. In this paper, in order to improve the strength of the composite, the surfaces of woodchips and bamboo fibers were modified by the alkali treatment. By examining the bending strength of the composites, it was found that the alkali treatment was effective in order to improve the bending strength of the proposed composite. Especially, it was clarified that the high bending strength was obtained in the case of combination of woodchips with the alkali treatment and bamboo fibers without the alkali treatment.

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To clarify the water absorption properties of CFRP and resin, water immersion tests of resin and CFRP were conducted. The cross-section of CFRP was observed to understand fiber placement inside CFRP. To analyze the water absorption of CFRP with different fiber placement, a new software program which only used a diffusion coefficient and a maximum water concentration in resin was developed. The calculated data were coincident with the experimental water absorption. Therefore, the adequacy of this program was confirmed. The analysis using this program suggested that fiber placement as close as the surface improved the resistant properties of CFRP against aqueous environment.

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In the present paper, press molding for thermo-plastic resin toughened by carbon nanofiber were discussed. Polycarbonate(PC) and vapor grown carbon nanofiber (VGCF) are used for the resin matrix and the reinforcement. In order to investigate and simulate the process molding process of the PC/VGCF composite by finite element method, the thermoviscoelastic property of the composites are estimated using unidirectional compression creep test. The creep functions were converted into relaxation function based on the convolution integral form of the basic equation using Laplace transform. Experimental testing for press molding of the PC/VGCF composites using Line & Space die has been carried out. The results of the molding profiles and those obtained by FEM analysis were compared to confirm the validity of the present analysis method based on thermo-viscoelastic theory.

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The surface of color and mechanical properties of Poly-ether-ether-ketone(PEEK) films are changed under ultraviolet light (UV) irradiation in low earth orbit (LEO). In this study, PEEK composites dispersed with titanium oxide (TiO_2) were developed to modify the mechanical properties of PEEK. The composites were compressed, being melted when they were produced. The performances and properties of the PEEK/TiO_2 nanocomposites were examined in terms of hardness and color change of surface after UV irradiation test. The results of hardness and UV irradiation test showed that PEEK/TiO_2 nanocomposites enhanced the hardness and improved the UV resistance of PEEK.

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The objective of this study is to investigate the effect of tensile stress on polymer materials in gaseous fluorine atmosphere. In this study, Poly-Ether-Ether-Ketone (PEEK) 0.4mm thin films were used. Tensile stress was given by tensile jig, which can apply various stresses to specimens. Direct fluorination was carried out by Takamatsu Teisan Co., Ltd. Fracture surface was observed by Scanning Electron Microscope (SEM). As a result, specimens were fractured during this treatment. Moreover, lower applied stress brought longer time to fracture. This trend is typical delayed fracture. Fracture surface clearly showed the existence of fracture origin. The analysis of Electron Dispersive X-ray Spectroscopy (EDS) demonstrated the fracture origin was caused by gaseous fluorine. The use of stress intensity factor evaluates quantitatively whether the delayed fracture would be occurred or not.

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This paper investigates the theimoelectromechanical 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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In this paper, the mixed-mode fracture problem of two penny-shaped or annular cracks in a functionally graded piezoelectric material (FGPM) strip is considered. It is assumed that the electroelastic properties of the strip vary continuously along the thickness of the strip, and that the strip is under electric loading. The crack faces are supposed to be insulated electrically. The problem is formulated in terms of a system of singular integral equations, which are solved numerically. Numerical calculations are carried out, and the stress and electric displacement intensity factors are presented for various values of dimensionless parameters representing the crack size, the crack location, and the material nonhomogeneity. It can be found that the normalized intensity factors are under the great influence of the geometric parameters and the effect of the material nonhomogeneity on the intensity factors depends on the geometric parameters.

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In stealth dicing (SD), a permeable nanosecond laser is focused inside a silicon wafer and scanned horizontally. A thermal shock wave is propagated every pulse toward the side to which the laser is irradiated, then a high dislocation density layer is formed inside a wafer after the thermal shock wave propagation. In our previous study, it was supposed that an internal crack whose initiation is a dislocation is propagated when the thermal shock wave by the next pulse overlaps with this layer partially. In this study, a two-dimensional thermal elasticity analysis based on the fracture mechanics was conducted. The internal crack propagation was analyzed by calculating the stress intensity factor at the crack tips and comparing with a threshold of that. As a result, validity of the previous hypothesis was suggested.

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In recent years, it causes the stress corrosion cracking, and the breakdowns of piping have occurred in the nuclear power generation plant. As a result, there is a possibility that a serious accident of radiation leak happens. The stress corrosion cracking is a phenomenon that the crack occurs in the material because of the interaction of the stress and the erosive environment, and the crack progresses at time. This study is about the stress corrosion cracking in the combination of the SCM435 steel and the boric acid solution. This combination has the feature that corrosion happens comparatively easily. This simulation is done according to acquired data by the experiment. The stress intensity factor is compared with an analytical solution, and the validity of this simulation is verified. Moreover, the application to the simulation including holes is verified as a result.

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A method of fundamental solution is presented for axisymmetric thermal stress problems of a transversely isotropic elastic circular solid cylinder. We apply fundamental solutions for axisymmetric thermal stress problems and axisymmetric body force problems of transversely isotropic elastic solids. Thermal stresses and temperature distributions of a solid cylinder subjected to a heat distribution at the end surface are considered by numerical calculations.

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Analytical solutions are presented for an asymmetric transient temperature field and the associated thermoelastic problem in a hollow hemisphere due to asymmetric heatings on the inner and outer hemisphere surfaces. The transient temperature field is derived by fourier sine transform, Legendre transform and Laplace transform. The associated asymmetric thermoelastic problem is solved by the use of thermoelastic displacement potential and Papkovich-Neuber displacement function.

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We propose the electromagnetic wave absorbers with controlled graded compositions (FGM type EM-wave absorbers) for a hollow cylinder and investigate an electromagnetic noise problem and a plane-strain thermoelestic problem of those FGM type EM-wave absorbers. The absorption layer with graded compositions is considered as a multilayered absorption layer. We present the analytical solutions of electromagnetic and temperature fields in the FGM type cylindrical EM-wave absorbers subjected to an irradiation power. The desired thermal stress distributions are also analyzed based on the stress function method. Numerical calculations are carried out for the FGM type EM-wave absorbers with absorption layers composed of epoxy resin matrix and conductive titanium oxide particles.

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In this study, the thermal conductivity of Sirasu Balloon/Epoxy composites was examined in order to evaluate mechanical and thermal property of the composites in temperature environmental conditions. The matrix resin of the composite is epoxy resin and its dispersion is micro glassy "Sirasu Balloon". The composite system developed is a kind of micro porous materials. A homogenization theory with multi-scale analytical method is described for evaluation of the thermal conductivity of the composites. From the experimental results, we proposed a unit cell model of micro porous materials for Finite Element Method (FEM) analysis. FEM analysis method was described for evaluation of the composite material system in temperature environmental conditions. By using the unit cell model and setting the mechanical and thermal properties of each material at the temperature, some numerical calculations were performed for the mechanical properties and thermal conductivity of composites. Analytical results made good agreement with experimental results in the temperature conditions.

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Assuming a "tensioned" circular saw in use, a theoretical analysis is performed to investigate the thermoelastic field and dynamic characteristics in a rotating annular disc that is subjected to the temperature and in-plane plastic strain distributions. Based on the plate bending theory, the governing equations for the axisymmetric in-plane behavior due to the thermal load, plastic strain, and rotation and the resulting unsymmetric anti-plane behavior are derived. Then, the solution of in-plane forces is obtained and the modal analysis of the disc is performed. Numerical examples are shown to investigate the thermoelastic field in the disc and the effect of the distribution of the plastic strain on the dynamic characeristics.

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In this study, the theoretical analysis of a transient piezothermoelastic problem is developed for a piezoelectric strip with two parallel cracks of different lengths under thermal shock loading conditions. The crack faces are supposed to be insulated thermally and electrically. By using both the Laplace transform and the Fourier transform, the thermal and electromechanical problems are reduced to two systems of singular integral equations, respectively, which are solved numerically. A numerical method is employed to obtain the time dependent solutions by way of a Laplace inversion technique. The intensity factors versus time for various geometric parameters are calculated.

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Experimental observation proved that an appropriate preheating of a glass plate brought more than 3 to 4 times improvement of processing velocity in a thermal stress cleaving. An electrical sheath heater of round bar type was used to preheat the prospective cleaving line. In the present study, the influence of preheating is investigated numerically by assuming a temperature distribution due to the preheating as a simple polynomial of the coordinate variable. The mechanism of high speed cleaving by preheating along the prospective cleaving line was well understood and the appropriate conditions of preheating were clarified.

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In this paper, the problem of an infinite row of parallel cracks in a functionally graded piezoelectric material strip (FGPM strip) is analyzed under transient thermal loading condition. The crack faces are supposed to be completely insulated. Material properties are assumed to be exponentially dependent on the distance from the bottom surface. The superposition technique is used to solve the governing equations. The transient temperature and thermal stress in an uncracked strip are the same as the previous results. This thermal stress is used as the crack surface traction with opposite sign to formulate the mixed boundary value problem. By using the Fourier transform, the thermoelectromechanical problem is reduced to a singular integral equation. The singular integral equation is solved by using the Gauss-Jacobi integration formula.The stress intensity factors for both the embedded and edge cracks are computed. The results for the crack contact problem are also included.

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The fracture behavior of a light cure composite resin under impact tensile loading was studied using single-edge-cracked specimens. The impact load and displacement were measured with a Piezo sensor and a high-speed extensometer, respectively. The load and displacement diagram, i.e. the external work applied to the specimen was partitioned into three parts: the elastic energy left in the fractured specimen, the nonelastic energy due to viscoplastic deformation and the fracture energy for creating new surfaces. These energies were then determined and correlated with the fracture load. Energy release rates were also evaluated, and the results were discussed.

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Brittle fracture behavior of a light cure composite resin was studied using a high-speed extensometer. The single-edge-notched tensile specimens were fractured with a special loading jig so that it could split and fly away after the fracture. The load and displacement diagram, i.e. the external work applied to the specimen was partitioned into three parts: the elastic energy left in the fractured specimen, the nonelastic energy due to viscoplastic deformation and the fracture energy for creating new surfaces. These energies were then determined and correlated with the fracture load. Energy release rates were also evaluated, and the results were discussed

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This paper describes the digital correlation method using the surface configuration data by the scanning probe microscope. The bending test is carried out on the table of the scanning probe microscope, and the configuration data on the specimen surface is obtained by the configuration analysis. After that, the estimation of the displacement field is carried out using the digital correlation method using the surface configuration data. In this paper, the accuracy of the estimation for the displacement field is investigated.

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We investigated a method to measure displacement distribution in the full view field of a CCD camera using digital image correlation (DIC) technique. This method intends to measure displacement field on a surface by comparing two images before and after deformation taken with a CCD camera. In this method, template matching of the corresponding points on the two images with accuracy less than one pixel is necessary to measure small displacement. In general, image sensor such as CCD and CMOS has scatter of sensitivity in each pixel. This scatter in sensitivity causes difference of gray level in each pixel and has a large influence on the template matching for the DIC method. In this study, we investigated difference of sensitivity in each pixel and we measured sensitivity difference for each pixel and also considered a method to calibrate gray level for different pixels.

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High accurate detection of the crack is an important technique for solving the fracture problem. There are some techniques for such a demand. However, there is no technique that can adjust to the crack on the pressure vessel piping, for example, the nuclear power plant. The fatigue crack which induced by thermal cycle occurs from the inside of piping which received severe environment. This study paid attention to digital image correlation method (DCM) as available technique in such an environment. A new crack detection technique on back surface of crack was developed in this study.

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A novel experiment method to generate a crack at the center of the interface between a Cu thin film and Si substrate is proposed. The specimen has a characteristic configuration where the nose is processed to L-shape. Crack initiation at the center of the interface has been recognized with in-situ TEM observation. By an analysis using a model where the specimen shape is precisely reflected, the critical stress for crack initiation is evaluated to be 1061 MPa.

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In this study, it is shown that the elasticity-plasticity transition point can be measured by attaching a strain gage to a place other than the specimen. To measure the deformation behavior of a material accurately, a sensor-like strain gage must be attached directly to a specimen. However, when it does not have the necessary area because of its attachment to the specimen, it cannot accurately measure the relationship between load and deformation. To measure the elasticity-plasticity transition point, it is not necessary to measure the relationship between load and deformation. The elasticity-plasticity transition point is measured from the relationship between stress and time using a newly developed intelligent universal test machine. The strain gage is attached to the holder connected to the specimen using a studs bolt.

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