An angle of a circumferential flaw in JSME's Fitness-for-Service Codes was restricted considering a measurement error of the flaw. In this study, pipe fracture probability were evaluated changing a flaw angle and a pipe diameter, and influence of some parameters on failure probability was examined. As a result, it was revealed that the influence of measurement error of the flaw depth is the biggest factor especially for the cases of long and deep flaw. To control failure probability at the same level as the conventional standard, it is the most effective to improve flaw measurement accuracy soast to depend on pipe thickness. Even in this case, the influence of the measurement error cannot be ignored when flaw is long and deep. Therefore, it is necessary to restrict the flaw depth according to the flaw angle, but this restriction is relaxed remarkably compared with the conventional one.

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In the case of bellows with a solid reinforcing ring, buckling due to internal pressure never happen. However, when a reinforcing ring is thin like a vent pipe bellows of the Mark-I PCV, buckling due to internal pressure may occur. This paper describes an examination of a simplified assessment method to evaluate buckling strength of bellows with hollow reinforcing ring under internal pressure load by using FEA.

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Creep void number density is one of the most important parameters to evaluate life of steel. As it is difficult to observe all the area of steel's section, there is arbitrariness in the decision of observation area when measuring creep void number density. In this research, we investigated the effect of the arbitrariness. Firstly, using scanning electron microscope, we made two-dimensional distribution of creep void number density by observing heat affected zone, where it is known to have a lot of creep voids, of three internal creep test specimens which are made of modified 9Cr-1Mo steel. In addition, we modeled people's decision of observation area and applied it to the creep void number density distributions of the specimens, and calculated the minimum value of observation value in older to evaluate accuracy of people's creep evaluation. Finally, using its result, we evaluated the effect of the choice of observation area and the uncertainty of observer's decision.

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To evaluate the rate of thermal embrittlement of type 316 low-carbon stainless steel weld metal at BWR operating temperature, aging test at 310℃, 335℃, and400℃ was carried out. Hardness of each ferrite and austenite phase of specimens was measured selectively by microhardness tester. Hardness of ferrite was increased apparently with all three aging temperatures, whereas hardness of austenite was not changed. Changes in the microstructure of ferrite aged at 310℃ for 11,000h and 18,000h were analyzed by TEM. It has been revealed that hardening of ferrite with aging at 310℃ was result of spinodal decomposition. Arrhenius plot for hardening rate of ferrite at each three aging temperature was plotted, and apparent activation energy was estimated. Using the apparent activation energy, hardening rate at 288℃ was discussed.

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Stress corrosion cracking(SCC), corrosion and erosion are one of the greatest concems in the structural matenals of nuclear power plants. Once the component is damaged, parts are needed to be replaced or repaired/cladded by welding. The replacement requires huge cost, and the repairs by welding can induce heat affected zone (HAZ) which is sometimes regarded as lowering the material performance. Cold spray (CS) technology is one of the "thick coating"techniques in order to apply for repairs of damaged parts. In this study, efect of heat treatment on microstructures and corrosion behavior of cold sprayed type 316L stainless steel were investigated. Accordirg to EBSD analysis, growth of crystal grains of specimens whose heat-treat temperature were beyond 800℃, and Vickers hardness of these specimens decreased. However, corrosion tests results demonstrated that corrosion resistance of heat-treated CS coating decreased.

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Advanced ultra supercritical (A-USC) steam power generation, in which high-pressure steam is raised to beyond 700℃, are being studied internationally in order to utilize high efficiency power generation. As candidate alloys for structural components in high temperature section, Ni-based superalloys, such as alloy 617, have been considered from high temperature creep strength, material workability, welding property. Since these materials are exposed to high temperature steam, it is desirable to investigate the effect of the environment on the degradation. Up to now, there are not many investigations about the evaluation of micro crack initiation and its growth behavior of Ni-based superalloys in high temperature steam environment. In this current investigation, in order to evaluate the influence of local oxidation and microstructural change on micro crack initiation and its growth behavior of alloy 617, constant stress tension tests were performed in a steam and a inert gas environment at 750℃. In both environments, fine grain structures were confirmed after the test. Such grain is thought to be formed as dynamic recrystallization under tensile loading at the high temperature. Oxidation along the recrystallized grains was not so significant and aluminum enriched oxides in addition to the chromium oxide were found. It is exhibited that almost all of the cracks initiated from the ordinary grain boundaries.

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To assure the structural integrity of a reactor pressure vessel (RPV) is one of the most critical issues to maintain the safe long-term operation of a nuclear power plant. In Japan, the assessment methods for RPV integrity using deterministic fracture mechanics, provided in the codes and standards, have been endorsed by the regulatory body. Meanwhile, a regulation on the fracture toughness requirements against PTS events with a probabilistic approach has been established in the U.S. In this paper, we describe preliminary research results obtained from the second-year activity of five-year project. Refering to the approach in the U.S., the through-wall cracking frequency (TWCF) for aging RPV in Japan against PTS events was calculated using a probabilistic fracture mechanics analysis code PASCAL3.

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Structural damage due to primary water stress corrosion cracking has occurred in reactor vessel penetration around bottom mounted instrumentation. In this paper, a benchmark analysis was conducted to evaluate the stress intensity factor for the assumed crack in a reactor vessel penetration, and the effect of dominant factors on the analysis results was examined.

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As a part of confirming allowance for maintenance standard and evaluation streamlining, mock-up evaluation tests were planned to study variability of collapse load for core shroud with cracks caused by SCC etc., and test conditions for core shroud were determined. 4 core shroud mock-ups were identically designed in the same cylindrical shape and size, and fabricated using SUS316L. Then simulation cracks by EDM were added to the depth of 67% of the plate thickness all around the outer surface of each mock-up. In order to collect the load-displacement characteristics, static load was loaded to all 4 cylindrical test mock-ups. Then the static-test results were compared to the allowance of the analysis to evaluate analysis adequacy.

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There are some possibilities that the current evaluation method for a core shroud with cracks provides overly conservative results and it is recognized that the margin should be evaluated in a quantitative way. In evaluating the margin, it is difficult to evaluate the variation of factors which affect buckling and collapse loads by simple repeats of FEM. Therefore, a structural reliability analysis method has been developed focusing on experimental design and response surface methodology which are commonly employed in the field of quality engineering. This method was validated with the results of tests which had been performed separately. Also, the margin of current evaluation method was calculated for the actual core shroud with cracks in a quantitative way.

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In order to evaluate margin quantitatively included in the analysis method of the rules on fitness-for-service, potential factors which may have effect on collapse load were identified and the probabilistic distribution of collapse load caused by the variation of these factors was calculated. The margin was evaluated quantitatively by comparing the probabilistic distribution of collapse load with the allowable limits calculated by the existing analysis method of the rules on fitness-for-service. This study presented approaches to a rational integrity evaluation method on the rules on fitness-for-service based on the quantitative margin evaluation.

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To evaluate an ultimate pressure capacity for severe accidents of Prestressed Concrete Containment Vessel (PCCV), an analysis model of PCCV for evaluation was constructed, and internal pressure analysis of the model was performed to compare with the pressure resistance test for the PCCV model with a scale of 1 to 4 performed at Sandia National Laboratories in the US. It was confirmed that the analysis result of the evaluation model was consistent with the result of experiments. An analysis using standard value for material properties was also performed to consider the versatility of the model. Ultimate pressure performance determined by the analysis was evaluated and found to be slightly lower than the actual value, however, the behavior of the whole structure leading to destruction and failure modes were confirmed to be consistent with experimental results. Therefore, applicability of evaluation methods was verified.

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To evaluate an ultimate pressure capacity for severe accidents of Pre-stressed Concrete Containment Vessel (PCCV), an analysis model of PCCV for evaluation was constructed, and zoom up analysis focused on liner ductile failure using standard value for material properties was performed to compare with the pressure resistance test for the PCCV model with a scale of 1 to 4 performed at Sandia National Laboratories in the US. Leak pressure was evaluated by the analysis and found to be slightly higher than the actual value, however, the behavior of the liner leading to failure mode were confirmed to be consistent with experimental results. Therefore, applicability of evaluation methods was verified.

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As one of responses to Fukushima event, structural integrity evaluation of Containment Vessel (CY) at severe accident has been promoted. This paper is intended to perform the elastic-plastic analysis of the pressure confirmatory testing of the Steel CV made in the past, to establish a method for analysis and evaluation at severe accident. Differences between test and analysis should be corrected using techniques ASME Sec. VIII which considers the effects of multiaxiality. Moreover, it is confirmed that the difference of equivalent plastic strain about 2.1 times between the test and analysis, caused by material discontinuities in the weld, for example. In ductile fracture assessment, it should be properly corrected this correction factor.

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Under elevated temperature condition, thermal ratchet phenomena, namely the cyclic accumulation of plastic deformation, is one of the typical failure modes. Ratchet phenomena occurs when the structures are subjected to uniform primary stress with cyclic secondary stresses. ASME boiler & pressure vessel code provides an evaluation method for thermal ratchet. However, this method is so focused on protecting thermal ratchet, that it could be too conservative under some conditions. Therefore, the rational evaluation method for thermal ratchet phenomena is needed based on its mechanism. In this paper, rational simplified evaluation method for cylindrical vessels is proposed using simplified model called "two bar model", which express stress redistribution mechanism of cylindrical vessels. This evaluation method enables simple prediction of both thermal ratchet occurrence and thermal ratchet deformation.

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Residual stress caused by welding process affects characteristics of strength and fracture of equipment and piping in nuclear power plants. Numerical analysis is powerful tool to evaluate weld residual stress in the actual plants. However, the three-dimensional precise analysis requires enormous computation time. In this study, the analysis code using iterative substructure method developed to speed up welding simulation was improved to simulate welding process of the plant equipment and piping. Furthermore, the improved analysis code was validated by measurements and other analysis results.

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When the flaws are detected m nuclear components by in-service inspection, structural integrity assessment is one of the most important procedures to assume the safety and reliability of nuclear power plants. Fatigue crack growth analysis should be performed for the technical judgment on continuous operation based on the Rules on Fitness-for-Service for Nuclear Power Plants of the Japan Society of Mechanical Engineers Code (JSME FFS Code) when the cyclic loading would be assumed. However, fatigue crack growth analysis for BWR components consisted of Ni-base alloy is currently impossible since the fatigue crack growth rate curve for Ni-base alloy in BWR water environment is not prepared yet in the JSME FFS Code. In this study, fatigue crack growth tests in BWR water environment were performed for Ni-base alloy. And fatigue crack growth rate curve in Paris law format was evaluated. As a result, fatigue crack growth rate curve for weld metal and heat affected zone (HAZ) was formulated, respectively. And the values of ΔK_<th> for less than 1s of rise time were determined.

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In order to evaluate the structural integrity of BWR reactor internals made of nickel-base alloys, fatigue crack growth rate curves expressed in Time-domain format were formulated. Effects of Stress ratio and Rise time of cyclic loading on fatigue crack growth rate in simulated BWR environment were evaluated in Time-domain format. As a result of this study, fatigue crack growth rate curves for nickel-base alloys (alloy 600 or alloy 182 and modified alloy 182) in BWR environment were proposed.

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When defects are detected by in-service inspections of the nuclear power plants in Japan, the allowable flaws can be evaluated in accordance with the rules on Fitness-for-Service for Nuclear Power Plants of Japan Society of Mechanical Engineers (JSME maintenance rules). Fatigue crack growth (FCG) analysis is one of the important actions for assessing the allowable flaw size. However a FCG curves for nickel base alloys in air condition is not provided in the current JSME maintenance rules. The paper summarizes the data based on the fatigue tests for the alloys and formulated FCG curves. The results show that the test temperature and stress ratio are dominant factors and the curves are the functions of these parameters. Threshold of stress intensity factor is introduced in the curves by taking into account the crack closure.

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The influence of crack growth on the fatigue life was investigated for a ramp change in the fluid temperature on the surface. The stress intensity factor was obtained by the weight function method considering the stress gradient in the thickness direction. The estimated fatigue life under the cyclic thermal loading could be 1.6 times longer than that under the uniform stress distribution. The critical size for the fatigue life determination was assumed to be 3 mm for fatigue test specimens of 10 mm diameter. By determining the critical size by structural integrity analyses, the fatigue life was increased under the cyclic thermal stress.

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Applicability of elasto-plastic parameter for evaluating stress corrosion cracking (SCC) growth rate was examined. Currently linear fracture mechanical approach has been applied for crack evaluation; even though some SCC is found in plastic deformation zone near welding areas where linear elastic fracture mechanics no longer is applicable. Authors have proposed elastic-plastic approach "equivalent stress intensity factor K_j" for evaluating SCC growth rate based on J-integral value, which is valid in both elastic and plastic stress fields. In order to verify the applicability of evaluation by K_j, SCC propagation test in compact tension specimens with varying specimen size and stress conditions were conducted in boiling water reactor environment. As a specimen, sensitized type304 stainless steel was used. When a crack growth rate (CGR) of SCC was evaluated by stress intensity factor K, linear relationship between K and CGR does not exist in the high K value, where CT specimens are out of small scale yielding condition. CGR increases exponentially according to increasing stress intensity factor K to exceed linear relationship. On the other hand when CGR was evaluated by elasto-plastic parameter K_j, linear correlation between K_j and CGR was confirmed regardless specimen size and stress condition. This suggests that by applying elasto-plastic parameter K_j for SCC behavior, CGR at high K value could be estimated easily with using a smaller specimen.

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Welds and heat affected zones have the distribution of the residual stress or the yield strength. The crack growth evaluation is conventionally conducted using stress intensity factor in those regions. However, the stress intensity factor may be invalid when the residual stress distribution or yield strength distribution changes in the vicinity of a crack tip. When the distributions exist, the crack growth evaluation should be conducted using a parameter considering the elastoplastic behavior near the crack tip. For that purpose, the authors proposed new correction method of the stress intensity factor using a differential term of that. The new method was demonstrated through the case study for stress corrosion cracking in a high temperature water environment.

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There is a possibility that the crack growth rate of stress corrosion cracking and fatigue crack depend on the value of ∂K/∂a (differential term of stress intensity factor) as well as stress intensity factor K. In this study, the effect of ∂K/∂a on crack growth rate was investigated during the fatigue test. Two types of specimens were prepared. One is CT specimen of which K increases under constant loading. The other is CDCB specimen of which K is constant. The effect of ∂K/∂a was clarified by comparing the CT specimen and CDCB specimen under same stress intensity factor. In addition, ΔK corrections considering ∂K/∂a were conducted for CT specimens. As a result, the crack growth rates in CT specimens were larger than CDCB specimens in the same ΔK. Corrected ΔK considering ∂K/∂a is mostly coincides with the value of the CDCB specimen. From those results, the crack growth rate varied due to the effect of ∂K/∂a in fatigue crack propagation was experimentally clarified. In addition, elimination of the influence of ∂K/∂a is possible by ΔK correction.

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It is very important to establish an evaluation method of the structural integrity of piping due to large earthquakes. The evaluation results by previously proposed crack growth evaluation method under seismic loading were in good agreement with the measurement results of piping crack growth tests using the simulated seismic load. In order to obtain J-integral formula for applying the proposed crack growth evaluation method to the pipe with circumferential semi-elliptical surface cracks, finite element analyses were performed. The seismic margin can be quantitatively evaluated using the proposed crack growth evaluation method incorporating the obtained J-integral formula.

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Estimation of ductile fracture behavior using GTN model in commercial FEA code was evaluated. The material properties of GTN model for Type 304 stainless steel were experimentally identified. Smooth bar and notched bar specimens were subjected to monotonic loading, and load-displacement curves were measured. Then, the tensile test was simulated. Material properties of GTN model were calculated from measured and simulated load-displacement curve with inverse analysis based on Bayes' theorem. Simulated load-displacement curve with GTN model of different curvature notched specimens were agreed well with the measured data. To verify the evaluation of ductile fracture using GTN model, flat plate with surface flaw specimen was subjected to monotonic loading. Ductile fracture of the flat plate was simulated using FEA with GTN model using calculated material properties. The simulated strain distribution was agreed to the measured strain distribution. The simulated load was less than the measured load at same displacement. The analysis with GTN model can estimate the load on the safe side and estimation of ductile fracture behavior.

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Austenitic stainless steel is used in the core internal structure of nuclear reactor from its high corrosion resistance and moderate fracture toughness. But the fracture toughness decreases by the neutron irradiation. The fracture toughness of irradiated stainless steel is highly uncertain and due to the lack of experimental results and the dispersion caused by the difference of experimental conditions. To perform a reliable structural integrity evaluation, the stochastic method considering the uncertainty in the strength of irradiated stainless steels are strongly demanded. In this study, we proposed an evaluation method of the variability of fracture parameters, in which the uncertain stress strain relationship is obtained from the Monte Carlo calculation using the constitutive equation of EPRI MRP-135. We demonstrated the finite element elastic-plastic analysis using the obtained 20 dispersed stress-strain relationships, and discuss the variability of the fracture parameters.

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Residual stress measurements inside a dissimilar metal welded joint were performed during thermal cycles using an engineering neutron diffractometer, TAKUMI in J-PARC/MLF. The materials used for the welded joint were SUS316L and NCF600 for base plates, and Alloy82 for the weld metal. Ultrasonic shot peening was applied to the welded joint after welding for introducing compressive residual stresses on the surface layer. Tensile residual stresses were observed at the depth of 4.2 mm of the welded joint at the room temperature. Behaviors of the tensile residual stresses in NCF600, Alloy82 and SUS316L were measured during thermal cycles. As the temperature increased, the tensile residual stresses in NCF600 and Alloy82 increased, whereas the tensile residual stress in SUS316L decreased. These phenomena in the temperature increasing process can be explained by the thermal expansion coefficient of each material.

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The general method is not always effective for the measurement of fatigue small crack growth properties by relation of accuracy and a device characteristic. Non-contact and the highly precise measurement are expected by the use of a magnetostriction effect to apply in this study. The small crack growth properties measurement by a magnetic field change with the magnetostriction effect that was one of a characteristic of magnetism of ferromagnetic substance was studied. Using a coil, a magnetic field change with magnetostriction effect was detected, and the waveform change of the output was inspected. The experiment result was revealed that the small crack affects a magnetic field change by a magnetostriction effect.

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X-ray diffraction contrast tomography (DCT) is a technique for three-dimensional grain mapping of polycrystalline material. Measurement of DCT has been conducted m SPring-8 and shape and location of grain can be determined by DCT technique using the apparatus in BL19B2. For evaluation of plastic deformation by DCT, tensile and cyclic loading was applied to the sample during the measurement of DCT. The diffraction spots belonging to certain grain appear over some continuous projection images. The rotation angle range where diffraction spot appear is defined as grain orientation spread, and the grain orientation spread was counted in tensile tests and fatigue test. In the tensile test, the grain orientation spread increases in the plastic deformation. In the fatigue test, grain orientation spread increases with increasing m the number of cycles. It is possible to evaluate fatigue damage by DCT technique and using the grain orientation spread.

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In rolling contact fatigue (RCF), cracks are usually initiated from inclusions under the surface and propagated to the surface. In the present study, the micro computed tomography (μCT) imaging and laminography using synchrotron radiation in SPring-8 is applied for observation of RCF cracks. The compact RCF testing machine is developed to observe RCF crack behavior m-situ. In this testing machine, the steel ball rolls on the specimen, linearly and reciprocally, and a specimen can be attached and removed easily. Since the size of the sample for μCT imaging has to be limited by penetrative power, the sample for μCT imaging has 500μm×500μm cross-section. On the other hand, laminography can be applied to a sheeted material. The sample, where an artificial defect is introduced, is used for observation of crack initiation and propagation. It is found from this experiment that cracks initiate and propagate in the depth direction along the artificial hole with increasing the number of cycles. Flaking and RCF crack in sheeted sample are observed by laminography. RCF cracks which initiate and propagate under contact surface can be detected. The shape and location observed by laminography coincide with that by SEM.

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Microstructure and a fatigue crack propagation path inside a dissimilar friction stir welded plate between A2024 and A6061 aluminum alloys were visualized with synchrotron radiation computed laminography at SPring-8. A fatigue crack propagated in a different direction from the perpendicular to fatigue loading under the influence of the plastic flow pattern in the weld. However, the fatigue crack shape projected onto the loading direction was similar to a half penny shape, and the aspect ratio decreased with increasing fatigue life. There was an interface plane between A2024 and A6061 in the welding zone but the fatigue crack propagation was not affected by the presence of the interface.

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In this study, three dimensional FEM analysis and fatigue tests were conducted using the cross tension typed spot welded joints with artificial defect. The spot welded joints were machined with the circular hole as the artificial defect. Fatigue tests were carried out with the force ratio of 0.05 and the frequency of 1〜20 Hz. FEM analysis result showed the stress hardly acted in large part of the welded area except the slit edge region. When the stress singularity was evaluated by the fracture mechanics, the stress intensity factor was almost the same regardless of the defect size. In addition, fatigue test results indicated the spot welded joints with the artificial defect had almost the same fatigue strength as the joints which had no defect. Then, this study clarified the welding defect hardly affect the fatigue strength of the cross tension typed spot welded joints even though the welding defect whose diameter was 80% against the nugget diameter.

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Hydraulic excavators have a lot of welded joints. Performing fillet weld is easy and economical. However fillet welded structures have unwelded area which is to be origin of fatigue crack initiation. Although the groove and fillet weld is performed to decrease unwelded area, it is difficult to perform fillet weld on both side for attachment with box structure. And also the structure with groove does not match machine costs. Because of that, high accurate evaluation method is needed. Up to date, evaluation for unwelded area has been studied in many papers and there are many standard evaluations method for crack propagation of unwelded area. However almost the all papers investigated cross fillet weld, and there is few fillet welded investigation. Moreover it is uncertain that crack propagation evaluation for actual machine condition is match or not, because many actual machines have unwelded fillet weld, and influence of weld defect for crack propagation behavior is not clear. In this study, fatigue crack growth tests were carried out on fillet welded test pieces. A test piece is modeled as to the actual machine. As the results, there was little crack initiation life. Almost the all lifetime is crack propagation. And weld defect have an effect on the direction of crack propagation.

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Crack propagation tests of lead-free solder were conducted using center-notched plates under strain-controlled and load-controlled conditions. The waveform of displacement controlled tests is fast-fast (pp), slow-slow (cc), slow-fast (cp), and fast-slow (pc) with the strain range of 0.2 and 0.4%. Three waveforms adopted for load controlled tests are as follows: pp waveform having fast loading and unloading, cp-h waveform having tension-hold, and cc-h waveform having tension and compression hold. Creep J-integral and fatigue J-integral estimated from load-displacement relations were used to correlate the crack propagation rate The crack propagation rate of pp waveform was a power function of fatigue J-integral. The crack propagation rate under other waveforms were correlated to creep J-integral. SEM observation was performed in order to observe the microstructure around main cracks after removing the surface layer. Micro cracks were not observed in specimens for the cases of cc and cc-h waveforms, while they were found for the cases of pc and cp and cp-h waveforms. According to EBSD observation, the grain size near the crack tip decreased with the crack propagation rate.

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EBSD(Electron BackScatter Diffraction pattern) observations were conducted on damaged Mod.9Cr steel obtained by the creep and the creep-fatigue tests as well as unused material. In order to quantify accumulated strains due to creep and creep-fatigue damage, "EBSD strain parameter M_<εKAM>" was introduced based on KAM(Kernel Average Misonentation) maps obtained by the EBSD observations. Here, M_<εKAM> was defined as the product of area averaged KAM: KAM_<ave> and boundary spacing/pixel size ratio. As a result, M_<εKAM> showed a good linear correlation with creep strain components for creep and creep-fatigue damaged materials under the optimal magnifications and grain boundary identification conditions in the EBSD observations. Therefore, M_<εKAM> was thought as a good parameter corresponding to the creep strain component. M_<εKAM> was also successfully applied to evaluate the creep strain components in the area containing the vicinity of creep voids and creep-fatigue crack tips on the failed materials by creep and creep-fatigue.

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To validate the failure mode and assess creep-fatigue damage evaluation, a thick cylinder test model made of Mod.9Cr-1Mo steel was subjected to 1,873 cycles of accelerated thermal transient loading using a large-scale sodium loop through which liquid sodium at 600℃ and 250℃ flowed repeatedly, with the period of each transient being 2 h and 1 h, respectively. After completion of the test, liquid penetrant testing, a surface observation and hardness testing were performed to characterize failure mode. Based on the finite element analysis, creep-fatigue life was evaluated by applying the JSME FRs code. The failure cycles evaluated by rules described in the JSME FRs code was shown to have a safety margin of greater than 300 times for this system.

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Field emission-type scanning backscattered electron microscope observation were performed on a ferritic heat-resisting steel that contained 12mass% chromium and 2mass% tungsten to characterize subgrain structure. The size distributions of the subgrains were quantitatively evaluated before and after a creep-fatigue testing, respectively. It was shown that subgrains neighboring the prio austenite grain boundaries become coarse during the creep-fatigue testing. And the nanoindentation test were performed on coarse subgrain, and it was estimated that Vickers hardness was 150, and, in contrast, the hardness before creep fatigue was 200. It is suggested that the coarse subgrains neighboring grain boundaries plays an important role of the creep-fatigue fracture mechanism.

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It is known that the fatigue crack propagation (FCP) behavior of magnesium (Mg) alloy is sensitive to the environment, because the corrosion resistance of Mg alloy is rather poor. In the previous works, the authors had conducted FCP tests using some Mg alloys under controlled humidity, and concluded that the FCP rates could be accelerated by the humidity in air. In addition, the hydrogen microprint method had revealed that the hydrogen atoms diffused along the crack-wake. Thus it was expected that the acceleration mechanism of FCP rates could be attributed to both anodic dissolution and hydrogen embrittlement at the crack tip. However, it is difficult to estimate the both effects separately, and the influence of hydrogen on FCP behavior is unclear. In the present study, FCP tests on Mg alloy, AZ61, were performed in 3% NaCl solution. The cathodic potential was controlled to achieve the hydrogen charged condition without anodic dissolution to figure out the effect of hydrogen on FCP. The cathodic potential was set to -3.0V, which corresponded to the immunity region without corrosion reaction based on the Pourbaix diagram of Mg. The FCP rates accelerated under hydrogen charged condition compared to those in dry air.

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TiNi shape memory alloys (SMA) receive the great attention because of their unique shape memory properties and commercial potential. However, TiNi alloys are apt to absorb hydrogen and deteriorate in various hydrogen environments, and the behavior of TiNi alloy fatigue life under the hydrogen environment has not been elucidated yet. By comparing fatigue test in air and fatigue test in hydrogen environment, the fatigue life of later clearly decreased than the other. At this time, a brittle layer was not formed on the fracture surface of the specimen for fatigue test in hydrogen environment However, macroscopically fracture surface was showing signs of brittle fracture. Furthermore, by comparing fatigue test in hydrogen environment and constant stress test and SSRT, the relationship between maximum stress and charging time showed good agreement with each other in low stress area about 300 MPa. On the other hand, in high stress area about 1000 MPa, large difference can be seen in the life of each. Therefore, the destruction under high stress amplitude is controlled by the damage due to stress fluctuation. On the other hand, destruction under low stress amplitude is controlled by the hydrogen embrittlement and the maximum stress.

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Because of its excellent high-temperature strength and high resistance against stress corrosion cracking, modified 9Cr-1Mo steel is widely used as the materials in high temperature energy equipment. However, the occurrence of high cycle fatigue damage at high temperature has been concern. Therefore, in order to clarify the characteristics of high-cycle fatigue of modified 9Cr-1Mo steel, a high temperature rotary bending test was carried out. As a result, S-N curve indicated that fatigue limit did not appear within the range of 10^8 cycles at temperatures higher than 500℃. And it was clarified that fatigue cracks always started to occur at the surface of the test samples.

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In the present study, fatigue tests were performed on Bi-brass with different microstructures to investigate effect of microstructure on its fatigue properties, i.e., S-N curves, fatigue crack initiation and crack propagation behavior at various temperatures. For these purposes, successive observations of the specimen surface during fatigue process were conducted using a replication technique. The results obtained were analyzed with linear elastic fracture mechanics.

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The fatigue behavior of single crystal silicon wafer was examined under bending load in two different environments, as in lab air, in hydrogen gas environment to see the effect of hydrogen (H_2) on the lifetime of silicon. It was well known, that the relative humidity has an effect on the lifetime of silicon. The obtained fatigue lifetime of silicon in hydrogen was short, as in humid environment. This fact means that the hydrogen had an influence on the fatigue properties of silicon as like the relative humidity in the surrounding atmosphere.

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In order to improve both of the fatigue strength and wear resistance of commercially pure titanium (CP titanium), a low temperature nitriding process was developed. Cold rolling was performed as pre-treatment of plasma nitriding in order to create fine grains which accelerate the diffusion of nitrogen into materials. Thick compound layer was formed on the surface of the nitride CP titanium pre-treated with cold rolling, resulting in showing high hardness in comparison to the only nitrided one. And, it was clarified that the low temperature nitriding process (600 ℃) prevented the grain-coarsening of CP titanium. On the basis of microstructure observations, the effects of low temperature nitriding on the 4-points bending fatigue properties of CP titanium were evaluated.

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Fretting fatigue behavior and mechanical property of Ti-6Al-4V coated with titanium nitride (TiN) by ion beam assisted deposition were investigated. To investigate the influence of mixed layer on the fretting fatigue behavior, TiN were deposited of an acceleration voltage of 0.2 and 2keV. Mixed layer became thick with an increase in acceleration voltage. Adhesion and wear resistance improved with increasing acceleration voltage. TiN coating increase the fretting fatigue life. The fretting fatigue life of the specimen coated with TiN of an acceleration voltage of 2keV was two times longer than that of the specimen coated with TiN of an acceleration voltage of 0.2keV. In conclusion, thicker mixed layer caused higher adhesive strength and wear resistance, resulting in long fretting fatigue life.

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Anodic oxide layer was formed on A5052 aluminum alloy, and subsequently DLC was deposited on it to fabricate DLC/anodic-oxide hybrid coating. Rotating bending fatigue testes have been performed using the hybrid-coated specimens with different thicknesses of anodic-oxide interlayer. The interlayer thicknesses were 10 and 50μm, where the thickness of DLC film was fixed as 3μm. The specimens without coating, with DLC single layer and with anodic-oxide single layer were also used for comparison. The fatigue strengths of the specimens with oxide layer were lower than those of the base metal without coating because oxide layer had pin-hole defects and the defects could be fatigue crack initiation sites. However, when DLC was deposited on the oxide layer to fabricate DLC/anodic-oxide hybrid coating, fatigue strengths were improved. The hybrid-coated specimens with the interlayer thickness of 10μ had higher fatigue strength than the base metal and those with the interlayer thickness of 50μm. Thin DLC layer with the thickness of 3μm could have suppressed the cracking in interlayer, and led to the improvement of fatigue strengths than the base metal. When the interlayer became relatively thicker compared with the DLC film, such as 50μm, DLC film could not suppress the cracking in interlayer, resulting in the lower fatigue strengths.

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Roller burnishing (RB) and friction stir processing (FSP) were applied to a cast aluminum alloy, AC4CH-T6, to improve the fatigue properties. In order to investigate the effects of RB and FSP on the fatigue properties, fatigue tests have been performed using the roller burnished, the friction stir processed and the untreated specimens. The RB specimens exhibited higher fatigue strength than the untreated specimens. This improvement is attributed to the increase in hardness and compressive residual stress by RB. On the other hand, in the FSP specimens, fatigue strengths were also significantly improved compared with the untreated specimen due to the elimination of casting defects by the FSP.

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This paper is to propose a method to predict the fatigue limit of the material having a defect of any shape. The 5056 aluminum alloy with Mg added has a fatigue limit, but in the case of specimens with Micro-Hole or smooth specimens, the fatigue crack is not initiated in the fatigue limit. Under these circumstances, the fatigue limit is equal to the fatigue crack initiation limit. Therefore, the following two experiments were carried out to elucidate the material property of5056 aluminum alloy adding Mg: (1) Fatigue test of notched specimens for the prediction of the fatigue limit in the area where the fatigue limit is equal to the fatigue crack initiation limit. (2) Fatigue test of Pre-Cracked specimens when a defect has sufficient stress concentration to initiate the non-propagating crack. From (1) and (2), we propose a method of predicting the fatigue limit of materials having a defect of any shape with a minimum number of fatigue tests. Furthermore, to test this method, we examined whether theoretical values and test results are equal for some specimens with Micro-Hole.

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In this study, the fatigue properties of aluminum die-casting alloy (JIS ADC10-T6) were evaluated quantitatively by means of √<area> method. Fatigue tests were performed in ambient air by means of a dual spindle type rotating bending fatigue testing machine for two types of the specimen; one is an hourglass type specimen and the other is a smooth specimen having four artificial drilled holes of which √<area> were ranged from 200 to 500 μm. After fatigue tests, fracture surfaces and artificial defects were observed using an optical microscope and a scanning electron microscope (SEM). As results, all hourglass type specimens failed from casting defects. In the case of the smooth specimen having four artificial drilled holes, fatigue limit decreased as artificial defects became large. According to the results of fatigue tests, it was clarified that the fatigue limit estimation proposed on the basis of results for JIS ADC12 could estimate the fatigue limit of JIS ADC10-T6.

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Several plates had been sampled from a large-scale cast aluminum alloy, AC4CH, ingot. Subsequently, rotating bending fatigue tests and microscopic observation had been conducted using three kinds of specimens with different solidification rates. The shape of pores, hardness and dendrite arm spacing (DAS) were affected by the solidification rates, while the fatigue strengths of three specimens were insensitive to the rates. The lower limit of fatigue strengths were estimated by means of extreme value theory. When separately-located pores were dominant in the specimen, the prediction was inconsistent with test results. The modified counting method of pore size was proposed to improve the accuracy of the prediction.

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Tensile tests and fatigue tests were conducted with a α-brass ultra-fine grains (UFG) from 1 to 5μm diameter produced either by severe plastic deformation through equal angular pressing (ECAP) or multiple rolling, where the minimum grain size obtained by ECAP was 4.9 μm, and 1.0 μm by the multiple rolling. The proof stress, tensile strength and fatigue limit were increased with decreasing grain size, and Hall-Petch relationships were established. The relationship, however, depended on the thickness of specimen, i.e., those were lower for thin plate. The proof stress increased by ten-fold by the grain refinement, while the tensile strength increased by two-fold. The fatigue strength also increased; however, the effect was not as much as the static strengths.

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