The polymerization shrinkage of a light-cured composite resin was studied using artificial cylindrical cavities to examine the relations between the hardness H_v the cavity depth h and the irradiation time. The hardness H_v and modulus E were also measured using the tensile specimens to correlate H_v and E. The parameters H_v and E were determined as functions of h and irradiation time. An analytical model was proposed to study these parameters as functions of h and the irradiation energy.

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Frequency characteristic of the optical fiber acoustic emission (AE) sensor integrating both of the sensing and the reference fibers into the sensing head for measurement in water was investigated. The characteristics of the sensor was evaluated by comparing the each waveforms detected by the optical fiber sensor and the PZT sensor having the known response function. It was demonstrated that no significant resonance is appeared in the range of 200 to 1200 kHz from the results of the experiment using the artificial AE source caused by pencil lead breaks. Dependence of the incidence direction of AE waves on the characteristics of the sensor was also discussed based on the experimental results using a cylindrical vessel. It was found that more flat characteristics is shown in the case of propagating AE waves toward the longitudinal direction of the sensor.

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A material shift in optical components from glasses to polymers has been facing a peculiar problem of larger birefringence characteristic. Birefringence causes an inherent error in optical systems. Here, an optimization of various types of controllable factors based on the inverse analysis is proposed toward elimination of such birefringence distributions. As a single parameter for evaluating birefringence through the design, manufacturing and in-service processes, we adopted stresses which can be converted from the stress-optical law or the Wertheim law. After formularization of the proposed method, its applicability was examined through simple numerical simulations. It is shown that ill-posedness of the problem can be overcome by introducing the L-curve method although further improvement is still required.

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This study aims to estimate of stress fields of real notched plates that are subjected to large deflections. The general solutions of von Karman equations on this problem does not exist, therefore the authors try to estimate a stress fields of large deflection problem by superposing stress fields of two soluble linear problems, a bending problem and a plane problem. This paper provides the approximate procedure to estimate of stress fields in a circular-holed plate subjected to large deflections using strain gages and the equations on stress fields near a notch root in a plate subjected to out-of-plane bending and in-plane deformation. Unknown coefficients of the equations are determined by the stress values from rosette-type strain gages using the method of least squares. The rosette-type strain gages are located on circular arc whose radius is 1.5 times the notch root radius. The estimated maximum stress values at a notch root are compared with those by the finite element analyses. The estimated results are approximate to those by the finite element analyses in the cases when the ratio of the maximum deflection to the plate thickness is less than 0.8. In these cases, the membrane stress is large enough for problems of large deflection.

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The Prandtl-Reuss constitutive equation is used to describe the relationship between strain and stress in the theory of elasticity and plasticity. This constitutive equation is expressed separately for the elastic and plastic regions. It was shown that the boundary between elasticity and plasticity can be clearly measured using an intelligent universal test machine. It was proposed that the relationship between stress and strain in both the elastic and plastic regions can be expressed as a single constitutive equation. In this study, it was shown that the relationship between stress and strain can be explained by applying the complementary function method in the elastic and plastic regions.

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The Crack occurs in the structural bodies and labotest type specimen for the working loads. The types of its crack modes is clarified to pure basic modes and mixed modes crack as shown to the standard three types. The Mode I type crack initiate and propagate in the uniaxial tensile stress, the other hands, the mixed mode cracks with combining the basic mode cracks initiate and propagate in the multiaxial stress. Although the mixed mode cracks are the Mode II and/or Modeffitype with Mode I type crack, it is usually called that Mode I + Mode II or Mode I + ModelItype crack. That's fact and results have been reported as the specialized studies results and conclusions. In this technical report paper, the author confirmed specialized ordinary researches under the simply evaluation and judging with the consideration and reviews for the previous study's results and successes for the papers in the Univesity, Graduate School and Companies.

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In order to obtain information about fracture mode of austenitic stainless steel fatigued at 700℃, rotating bending fatigue tests were carried out for stainless steel SUS304-HP at 700℃. Internal fractures with fish-eye pattern occurred under long fatigue life region.

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High temperature fatigue crack growth tests under multiaxial stress conditions were conducted for SUS304 stainless steel. By using DC electrical potential drop (PD) method, multiaxial crack growth was evaluated. Under the conditions, two types of fatigue crack growth were observed; "tensile type" crack, which propagates along the direction, φ, perpendicular to the maximum principal stress, σ_1 and "shear type" crack, which propagates along the direction of maximum shear stress, T_<max>. For each crack growth type, cyclic response of deformation during fatigue tests and micrographs of the fracture surface were examined. From these results, crack growth mechanisms were discussed.

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Loading frequency dependence of near-threshold fatigue crack growth behavior of Ni-based conventionally cast superalloy at elevated temperatures was examined in the air and in a vacuum below 5.0×10^<-4> Pa using constant K_<max> and ΔK decreasing test method. Loading frequency was changed from 30Hz to 3Hz and vice versa, and crack growth rates at f=30Hz and 3Hz were compared. It was found that the crack growth behavior at 850℃ and 900℃ in both environments was dependent on loading frequency below the so-called "apparent threshold". Observations of fracture surfaces after those experiments were made by digital microscope and SEM. Characteristics fracture surfaces were observed.

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Thermal cycle fatigue tests are carried out using Cu/Si_3N_4 ceramic substrates under four types of thermal cycle conditions including high temperature region and subsequently the residual strength of the ceramic substrates subjected to the thermal cycle is measured by four-point bending tests in order to investigate effects of thermal cycle conditions on thermal cycle fatigue strength properties of Cu/Si_3N_4 ceramic substrates. About 20 percent reduction in the residual strength of the ceramic substrates is seen in thermal cycle conditions of 0 to 125℃, -40 to 125℃ and -40 to 250℃ for 1000 cycles. Whereas in the case of -40 to 400℃ for 1000 cycles including high temperature region, the residual strength drastically decreases compared with those in other thermal cycle conditions, and the more than 80 percent reduction in the residual strength is observed.

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This study examined the deformation behavior and fatigue crack initiation of a carbon-steel film under cyclic shear loading. As a result, two relations about fatigue behavior were found. Observations indicate that the occurrence of the slip ratio is not inline content of the pearlite and grain size,can be evaluated by the ratio of grain size and thickness of the thin film. On the other hand, generating of a crack has the great influence of pearlite content.

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In order to examine the fine granular area (FGA) formed timing in high cycle fatigue for bearing steel, the rotating bending tests were carried out under two conditions of decremental step loading. The cumulative damage value of stress cycles at the high stress level was 0.1 against the average of the fatigue life in the interior inclusion induced fracture. And the cumulative damage values were 0.14 and 0.32 against the average of the fatigue life in the surface induced fracture. In this experiment, the roll processing performed in order to improve a fatigue life in surface induced fracture mode. From the experimental results, the different fine granular area aspect from stress constant cases was observed.

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In order to study the effect of the interaction and coalescence of multiple surface cracks by slit type surface crack on static fatigue behavior of brittle materials such as glass and ceramics, the various slit length were introduced on the surfaces of plate specimens of glass ceramics by scriber. Glass ceramics used for the experiment is a N-0(about 0.05μm grain size) and N-11(about 1μm grain size) material. It was found that the time-to-failure for a given applied stress significantly decreased with a increase in the distance of the slit length. However, the static fatigue life does not lower in case of the long slit length in the N-11.

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The following conclusions were obtained as a result of examining the fatigue strength characteristic from observation of fatigue testing and a fracture paying attention to damage to the resin / fiber interface in GFRP which denatured resin. 1) The damage mechanism was the same although Young's modulus fell PDMS compared with PC. 2) In fatigue testing, the life difference in a high stress region is based on the difference in a damage mechanism. 3) It generates with early elongation and damage results in destruction through the rigid fall by the crack progress following it.

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The effects of surface roughness on low cycle fatigue properties were investigated by strain-controlled fatigue tests using specimens of austenitic stainless steel finished by two different methods: machining and mirror polishing. During fatigue tests, the surface roughness of each specimen was measured, and crack initiation and propagation were observed using cellulose acetate replicas. As a result, the fatigue life of mirror polished specimen was longer than that of machined one. It was shown that the surface roughness affected the fatigue life. The change of surface roughness of each specimen showed the same increasing tendency with respect to the number of cycles. However, around the end of fatigue life, the surface roughness of mirror polished specimen became larger than that of machined one. In the damage process, the crack initiated at the very early stage of fatigue life. The crack growth rate was small until the middle of fatigue life; however, it increased rapidly after that. The surface roughness affected the crack initiation, and that is the reason why the fatigue life and the change of surface roughness were different between each specimen.

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This study aimed to examine the effect of ultrasonic shot peening (USP) process on the fatigue strength of stainless cast steel JIS SCS6 for hydraulic turbine runner. Fatigue test was carried out in laboratory air room temperature using the specimens which was treated USP (USP specimen) and was not (Virgin specimen). It was found that the modified layer formed by USP process had high hardness and compressive residual stress. The fatigue strength of USP specimen rose about 60% in comparison with Virgin specimen. The fatigue crack in each type specimen was observed in detail by using plastic replica technique. The fatigue crack initiation life of USP specimen was more extension than that of Virgin specimen. The fatigue crack propagation rate of USP specimen was lower than that of Virgin specimen. The modified layer formed by USP process affects the fatigue crack initiation life and the propagation rate. The two reasons are the factor of the improvement of the fatigue strength by USP process.

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In the present study the torsion fatigue behavior of SUS 630 steel has been investigated by conducting torsion fatigue test using servo hydraulic torsion fatigue testing machine at 20 Hz frequency. The shape of surface crack under torsion loading conditions has been studied by using replica technique and crack nucleation mechanisms were studied by examining fracture surface using scanning electron microscope. The results showed that the crack nucleation mechanism changes as the number of cycles to failure moved from low cycle to high cycle regime.

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In recent years, global warming is a serious problem. Therefore, Diamond-like carbon (DLC) film has been attracting attention in order to reduce greenhouse gases. However, the properties of DLC coated material are not well understood. This study aimed to examine the mechanism of fatigue fracture and properties of DLC coated material. Bending fatigue test was carried out. Fatigue strength was improved by DLC coating. From the fracture surface observations, it was found that the fracture origin of both virgin and DLC series was slip. There was no difference in the fracture origin between DLC series and virgin series. It was observed that the crack initiation life of DLC series retardate than virgin series by replica method. This reason was thought that the compressive residual stress of depositing DLC film control crack initiation.

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The ultrasonic fatigue test is important technique to reveal very high fatigue behavior of engineering materials. Because of resonance phenomenon using technique, testing specimen have stress and strain distribution. This distribution is estimated by theoretical calculation. Actual effective stress distribution, however, may differ from estimated distribution. Therefore, the understanding and measurement of actual distribution is important to this technique. In this study, actual stress distribution measurement is discussed with self-heating distribution measurement by using thermo-graphic measurement. Moreover, specimen shape effects and strain amplitude dependency on stress distribution are also discussed. Finally, thermo-graphic measurement has possibility to describe stress distribution of the ultrasonic fatigue specimen.

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To improve fatigue strength and to reduce weight of a machine, surface treated materials are commonly used. Fatigue strength can be improved by the surface treatment, however, the estimation method of the fatigue life is not well established. To estimate a fatigue life, it is important to divide the fatigue life into crack initiatin life and crack extention life. In this study, a strain gage metod is proposed to detect a small crack initiation life accurately. Bending fatigue tests of round notched bar specimens with nitriding and with carburized quenching, and detect the small crack initiation with this method to find the difference of the fatigue crack initiation and propagation behaviors.

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Orientation changes during fatigue crack initiation process in ferrite steels with different grain size and chemical composition were evaluated by the electron backscattered diffraction(EBSD). EBSD measurement and fatigue test were alternately carried out using small specimen. Crystal rotation was evaluated at the same point before fatigue testing and after fatigue testing by digital image correlation. The crystal rotation is relatively larger at the crack initiation site. The average of rotation angle in the observed area is increased and then constant at crack initiation. The constant value is about 2.0deg regardless of grain size and chemical composition. This result suggests that crystal rotation based on the crystal direction before fatigue testing is quantitative parameter for evaluation of fatigue damage dominating fatigue crack initiation.

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The change of the microtexture of the electroplated copper thin films was applied to the evaluation of the accumulative damage under random load. The micro texture of the electroplated copper thin film at the edges of micro slits formed in the film was found to change as a function of the amplitude of the applied cyclic loading. The life of the change was expressed by the modified Miner's law wlich is applied to the evaluation of the accumulated damage of materials under fatigue loads. Thus, it is possible to apply this method to the evaluation of the accumulated load

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This paper described a fatigue damage evaluation method for variable multiaxial fatigue loadings. The progress of computer and finite element analysis technologies enables designers to solve the complex stress or strain states in actual components even though external forces change with time. The designers are now in need of a method or technology to evaluate the analysis results properly. Considering such background, the authors had developed the visualizing tool to display the loading history on virtual space and quantify the multiaxiality. In this study, six kinds of low-cycle multiaxial fatigue tests for Ti-6Al-4V were conducted with the various combinations of axial and shear strains. Then the test waves were counted by the visualizing tool, and the multiaxiality also computed for all tests. The fatigue lives were predicted for all tests by using the information obtained from the developed tool and the Miner's rule. The method was confirmed to predict the fatigue lives with the accuracy of the factor of 2.

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Since fatigue strength at very high cycles has been found to decrease drastically in some high-strength steel, it has become very important to establish a very high cycle fatigue test using ultrasonic loading because of its reasonable short test time. However, there are two issues: self-heating of specimen and load frequency effect. It was confirmed that the temperature of a specimen increased with the square of the applied amplitude of displacement. The combination of the forced air cooling and intermittent loading was effective for minimizing the increase of the specimen temperature within 50℃. Load frequency effect was observed in the ultrasonic fatigue test of Mod.9Cr-1Mo steel.

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The giga-cycle fatigue properties of high-strength steel are important to maintain and manage the equipment. In the present study, the rotating bending test and the ultrasonic loading test up to 10^8 cycles are carried out using the 800MPa grade high strength steels in order to clarify the giga-cycle fatigue of high-strength steel. One of the several specimens failed due to internal fracture over 10^7 cycles in the ultrasonic loading test. It was clarified the origin of fracture on specimen which failed over 10^7 cycles is inclusions, which has large profile area, by fractography.

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High cycle fatigue tests under push-pull axial loading were carried out on SNCM439 in vacuum and air environments to clarify the mechanism of sub-surface fatigue fracture. To reveal the Effect of vacuum environment on defect size dependency of fatigue limit σ_w, specimens with small artificial defects were tested. As a result, the following conclusions were obtained: (1)The vacuum environment increased the fatigue lives and lowered the fatigue limits. (2)The S-N curves in vacuum showed a gentle sweep although those in air indicated a clear knee point with a level line. (3)Defect size dependency of σ_w, is considered different in each environment. (4)Sub-surface fractures can be quantitatively simulated by vacuum fatigue tests using specimens with an artificial small defect.

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The bending fatigue tests were performed using the small sized specimens of AZ31 magnesium alloy fabricated by the focused ion beam (FIB) processing to investigate the scale effect on the fatigue behavior. For the fatigue test of the small sized specimens, the fatigue testing apparatus was constructed using the piezo actuator and the high-resolution microscope to control very small displacement. The shape of the small sized specimen was micropillar with the rectangular cross section of 3μm x 8μm and the height of 40gm. The fatigue tests of micropillar specimens were successfully conducted, and the fatigue strengths of the micropillar specimens were higher than those of the bulk sized specimens. The fracture surfaces of the micropillar specimens were rather flat without striations compared with those of the bulk specimen.

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Fatigue crack propagation of the friction stirred welded joint of AA6063-T5 plate was investigated. The fatigue crack propagation rates(FCPR) were experimentally evaluated by means of the specimens in which the initial notch was introduced at the different site; e.g., base metal site, center part of stirred zone, metallurgically heat affected zone, and thermo-mechanically affected zone. Through the work, special attention was paid to the difference in the crack propagation rates those might be influenced by the inhomogeneous microstructures and mechanical properties relating to the stirring process. The effect of 2 stage friction stir welding process on the FCPRs was also experimentally evaluated..

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The effect of Laves phase embrittlement on the fatigue behavior in type 347 austenitic stainless steel was investigated. When this material is exposed to the temperature range of 700-900℃, the precipitation of the Laves phase occurs, resulting in the embrittlement of the material which is known as the Laves phase embrittlement. Rotary bending fatigue tests have been conducted in laboratory air and in 3%NaC1 solution using a niobium-containing austenitic stainless steel, type 347 aged at 700, 800 or 900℃. In laboratory air, the fatigue strengths were improved by the aging at 700℃ due to the fine Laves phase precipitation in γ-phase. Whereas the aging at 900℃ decreased fatigue strengths, which could be attributed to the coarsening of precipitated Laves phases. In 3% NaC1 solution, the fatigue strengths of 700℃ aged specimens were lower than those in laboratory air. It is considered that the sensitization took place during the heat treatment, where chromium-depleted zones were formed along grain boundaries.

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Giga-cycle corrosion fatigue behavior of 12 Cr martensitic stainless steels in NaCl and NaOH aqueous solution were summarized mainly on the basis of the author's experimental results. Then giga-cycle corrosion fatigue behavior of austenitic stainless steels such as SUS304,SUS304N2, SUS316, 2.5%Cr containing steel and YUS270 super stainless steel are demonstrated on the basis of the author's recent experimental results. Giga-cycle corrosion fatigue behavior of SUS329 duplex stainless steel is touched on briefly. The reduction of giga-cycle corrosion fatigue strength of stainless steels is depending on the kind of stainless steel. It can be concluded that the reduction of corrosion fatigue strength of martensitic, austenitic and duplex stainless steels is due to the corrosion pit formation at corrosion fatigue crack initiation area.

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In case of a fuel-cell vehicle, high-pressure H_2 gas is indispensable for a long running range. Also some components used in the Hydrogen Station exposed to a high-pressure H_2 gas. Although there are lot of paper for studying a hydrogen embrittlement (HE), there are few paper referred to the effect of high-pressure H_2 on the HE phenomenon. In this study, an effect of high-pressure H_2 gas on tensile and fatigue properties of stainless steel SUS316 was investigated by means of the internal high-pressure H_2 gas technique. Main findings of this study are as follows; 1) There are little influence of high-pressure H_2 gas to tensile and fatigue strength on SUS316 at room temperature. 2) It was verified that the internal high-pressure H_2 gas technique is very useful for easy experiment.

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Fretting fatigue strength of SUS304 was significantly lower in hydrogen than in air. One of the causes was adhesion between contacting surfaces and formation of small cracks. Therefore, impurities in hydrogen can have influence on fretting fatigue strength in hydrogen. In this study, small amount of oxygen was added to the hydrogen, and then fretting fatigue test of SUS304 was carried out in the mixed gas. The fretting fatigue strength in the mixed gas is in the middle between those in air and in hydrogen. Increase in friction force coefficient was also cause of the reduction of fretting fatigue strength in hydrogen. The friction force coefficient in the mixed gas was similar to that in air. There were oxidized fretting wear particles on the fretted surface tested in the mixed gas. Therefore, the increase in fretting fatigue strength by the addition of small amount of oxygen was achieved by mitigation of the adhesion between contacting surfaces.

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It is necessary to grasp wear properties of the materials under various kinds of lubrication conditions. Pin-on-disk wear tests were conducted for the above purpose using WJ2 type, i.e., lead free white metal. The lubrication environments were top water, two kinds of lubricating oil. The test was also conducted in atmosphere for a comparison purpose. The influence of the lubrication condition on the wear rate was investigated, and its mechanism was discussed on the basis of the experimental results.

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R-curve behavior of zirconia has been already reported by many researchers. On the other hand, the effect of cycling stress on cyclic fatigue behavior of zirconia has been also confirmed. It is important for the lifetime prediction on fatigue to make clear the correlation between the stress cycling effect and R-curve behavior. In this work, K_1-V curve of stabilized zirconia was obtained by crack length measurement method using thin metal film for indentation small crack. Also a rising R-curve could be obtained from stable crack growth by three point bend with the 0.025 mm/min for the small crack. The lifetime prediction for cyclic fatigue was obtained by assuming that the rising R-curve behavior is due to the crack tip closure disappeared by the cyclic load. The predictions could well explain the experiments.

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This study focuses on the method of predicting the fatigue life of materials subjected to random loading. Since random stress is rigorously expressed in frequency domain as stress power spectral density (PSD), the fatigue life should be predicted with the stress PSD. In this article, we propose a method of improving the accuracy of the fatigue life prediction with stress PSD in frequency domain. Although the method proposed by Dirlik is widely used for predicting the fatigue life in frequency domain, it often overestimates fatigue damage caused by large stress amplitude. To avoid this overestimation, we estimate the expected value of maximum stress amplitude from stress PSD and then use the expected value to adjust the probability density function of stress amplitude evaluated using Dirlik's method. The proposed adjustments were applied to the fatigue life prediction in the cases of typical random stresses observed on mechanical products, and as a result, it worked well to improve the accuracy of the prediction.

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Magnesium alloy is the lightest metal in practical material, and it has excellent specific strength, machinability, recyclability, and vibration absorption. In particular, extrusion material has been applied to the structures in terms of high-strength material can be obtained. In this study, fatigue tests were carried out in laboratory air using an extruded Mg alloy AZ61 to study the distribution of fatigue lives under the different stress ratios. During the fatigue process of the extruded Mg alloy, cracks were initiated from the inclusions existing on the specimen surface. The extreme-value distribution of the defect sizes was investigated experimentally in detail. The crack propagation behavior was analyzed using a modified linear elastic fracture mechanics parameter, M. The relation crack propagation rate vs. M parameter was found to be useful in predicting fatigue lives at different R ratios. Good agreement between the estimated and the experimental results at each stress ratio was obtained.

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For stainless steel, it was pointed out that fatigue life did not decrease due to mean stress because the mean stress caused plastic shakedown and that reduced the strain amplitude under the same stress amplitude. However, it may reduce the fatigue life of work hardening material due to the mean stress. In this study, the effect of the mean stress on fatigue life of cold-worked material was investigated in detail using Type 316 stainless steel which introduced 20% plastic strain. Axial fatigue tests were conducted in ambient air and room temperature. It was shown that fatigue life of stainless steel was not reduced by introducing the plastic strain because non-elastic strain amplitude of cold-worked materials under the same stress amplitude decreased due to the work hardening. Fatigue life correlated better with the strain amplitude than the stress amplitude regardless of degree of cold-work. It was found that fatigue life of the cold-worked material decreases with increase the mean stress because crack opening point decreased with increase the mean stress. It was concluded that fatigue life well correlated with effective strain range, which corresponded to the crack opening range regardless of degree of cold-work and mean stress.

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nternational Institute of Welding (IIW) recommends that fatigue strength of welded joints is evaluated by using Hot Spot Stress (HSS). In this study, the fatigue strength evaluation method with HSS was applied to welded test piece, in which a hanging structure of a thin plate box with railway vehicle was mocked up. HSS calculated by FEA model with welding beads showed good agreement with experimental result. And S-N curve of the thin plate structure, which was obtained by fatigue test of the hanging structure, gave lower slope than S-N curve recommended by IIW. (So, S-N curve would be determined for every thickness of plate.)

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The plastic deformation within a yield surface has to be described to simulate mechanical fatigue phenomena under macroscopically elastic condition. In this study, a phenomenological plasticity model is proposed for the description of the cyclic softening behavior observed for some carbon steels during so-called the high-cycle fatigue subjected to stresses lower than the yield stress. The model is formulated based on the unconventional plasticity model and is applied for materials obeying isotropic and kinematic hardening law. The mechanical responses and capability for evaluating the initiation life until fatigue cracking are examined briefly.

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Lead is added to traditional free-cutting brass. However, lead is dangerous to the human health and environment. So, Bi brass has been produced as an alternative to the lead brass. In this study, fatigue test was conducted at room temperature using the lead free brass, i.e., Bi brass. The material was clarified to be consist of three phases, a, R and Bi phases. A crack was initiated at Bi phase existing in specimen surface at the early stage of fatigue life. The Bi phase is much softer than the other phases. Prediction of fatigue life was carried out on the basis of crack propagation behavior. The predicted result was in good agreement with the experimental value. It was also clarified that the smaller the size of Bi phase, the longer the fatigue life.

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Fish eye failure that is unique fatigue fracture occurs in very long life region of high strength steel. The fatigue life of Fish eye failure dominated ODA (Optically Dark Area) around the fracture origin. A granular looking area of ODA is visible close to the crack initiation, fatigue life of Fish eye failure is almost exclusively spent propagating the fatigue clack in ODA. Therefore, to predict fatigue life of Fish-eye failure is important to know ODA of formative mechanism. In this study, fatigue and tensile test was performed in vacuum that simulated environment of subsurface failure and compared the result by the test condition. The observation of process when ODA is formed on the precrack tip was examined in order to make clear a mechanism of ODA formation.. Non-propagation of fatigue crack due to the fall of maximum stress. This is considered to be because for the crack opening stress to have been reached. The effective stress intensity factor range can arrange crack growth rate.

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Fatigue crack propagation of Ni-base superalloy718 casting was investigated at room temperature, using CT specimen of thickness of 6mm. A fracture observatin and section observation were carried out about the specimen. In addition, crystallographic orientation analysis by the EBSD measurement of polishing surface under the fracture was performed. As a result, at the domain of ΔK = 16-18MPa√m, crack propagation was diagonal and a fracture depended on the metal organization, at the domain of ΔK = 18-21 MPa√m, crack propagation was straight and the fracture surface was like ductility, and at the domain ΔK =21-30 MPa√m was the same as a low ΔK. At the domains of ΔK =16-18 and 21-30, fatigue crack propagation rate were slow. In the domain of ΔK=18-20, it was fast fatigue crack propagation rate and crystallographic orientation was near to (100).

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In order to investigate the ultimate strength of structures and components under the unexpected huge earth quake, it is necessary to understand the final fracture condition under static and cyclic loading conditions. This study compared the crack growth behavior under monotonic and cyclic loading conditions for carbon steel SGV410 used for pipes of nuclear power plants. Crack lengths were measured by unloading elastic compliance method. Fatigue tests were carried out by two kinds of methods, which are constant load amplitude and increasing load line displacement tests. With the increase in the number of cycles, the crack accelerated and then fractured. of fatigue crack growth characteristics coincide under the present test conditions regardless of specimen thickness. However, with increasing the J-integral range, ΔJI, crack growth rate accelerated and then unstable fracture occurred. Upper bound of the fatigue crack growth rate was the blunting line. Finally, the monotonic R curve becomes the upper bound characteristics of fatigue crack growth under the unstable fracture conditions. In fact, critical characteristics of fatigue crack growth are monotonic R curve.

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It is recognized that crack closure behavior is the important parameter that influence the crack propagation behavior. Fatigue crack was closed under the tensile load before the tensile load was completely removed. Until now, three crack-closure modes, i.e., plasticity-induced crack closure, roughness-induced crack closure and oxide-induced were proposed. In the present study, we investigated the place where the crack-closure occurred using both the aluminum alloy A6061-T6 which exhibits the plasticity-induced crack closure behavior and the carbon steel S25C which exhibits the roughness-induced crack closure behavior.

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It is necessary to investigate the elastic-plastic fatigue crack growth behavior under complex loading in order to evaluate an ultimate strength of actual structures. In this study, tension-compression fatigue tests for CT specimens and torsion fatigue tests for plate specimens with notches were performed for aluminum alloy A2017 to compare crack growth behavior under tension-compression and torsion loadings. In tension-compression fatigue tests, the fatigue crack propagation was share mode. J-integral range was calculated by empirical formula and crack growth characteristic was evaluated by J-integral range. In torsion fatigue tests, the fatigue crack propagation was share mode. As a result of fracture surface observation, it was found from crack front geometry that crack growth rate of surface was faster than that of inside. J-integral range of crack front was calculated by finite element method and crack growth characteristic was evaluated by J-integral range. These results corresponded to the mode II crack growth characteristics obtained under small scale yielding.

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To simulate large-scale fracture mechanics problems effectively, the partitioned iterative coupling algorithm can be employed. In the algorithm, the finite clement model is decomposed into a small domain and a large domain. The small domain contains a crack, while the large domain does not. In the small domain, advanced constitutive laws and criteria can be employed because of a small number of nodes. On the other hand, in the large domain, the decomposed model remains large-scale but becomes linear-elastic. Using the algorithm, fatigue crack propagation simulation with a three-dimensional finite element model is conducted for estimating the accuracy and the computation time.

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In order to clarify the small scale yielding condition in magnesium alloy, FEM analysis of the R-curve whose shape is considered to be the material characteristic shape was carried out. As an object material, magnesium alloy AZX312 was used. From the FEM analysis results, the shape of the R-curve of its first step when an initial crack size α= 200 μm is obviously different from those of α= 900μm and α= 2000μm. It is considered that the transition crack size from the small scale yielding to the large scale yielding may be between 200 μm and 900 μm. However, the threshold crack size given by the ASTM standard E399 is much larger than 900μm. The ASTM standard is based on experimental results of many materials, however, the standard does not consider the difference of Young's modulus of each materials. So, in magnesium alloy whose Young's modulus is low, the ASTM standard is considered to be not effective.

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In recent years, in order to estimate the residual life assessment of thermal power plants, creep damage evaluation method in heat affected zone (HAZ) has become more important. In this study, we aimed at elucidation of the three-dimensional microstructure of 9Cr-1Mo steel which is often used in high temperature conditions. We observed the three-dimensional geometry of fine grained HAZ using the "3D-EBSD method", and made the quantitative evaluation. It is suggested that both creep voids and grain are coarsening as damage progresses and this growth is occurring rapidly in the late stage of damage. In addition, according to the three-dimensional distribution, voids are often lined up in parallel to the direction of stress, and are present scattered around. Therefore considering the previous studies (1Cr-1Mo) that grain size does not change and voids are lined up like a crack along the grain boundaries perpendicular to the direction of stress, this growth model of creep voids in the fine grained HAZ of 9Cr-1Mo steel is significantly different from previous studies.

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To take advantage of the toughness mechanism of DN gel and explore its possibility for engineering application as the structural member, the information on the mechanical behaviour of DN gel under various loading conditions is indispensable. Therefore, in this study, we at first perform the simple tensile test to clarify the dependence of the mechanical response of DN gel on the loading history and on the loading speed. Continuously, we design an experimental equipment for the 2-axial compression of DN gel and the mechanical response of DN gel under 2-axial compressive loading condition is investigated. It has been shown that the designed experimental equipment can operate easily to a considerable degree.

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Freestanding nano-films generally fracture at a small strain less than 1%. It is due to the high yield strength and the localized fracture by inevitable defects. Since the localized fracture such as crack propagation is accompanied with large plastic deformation, the evaluation of large strain plasticity is important to explore the mechanics of fracture in nano-films. The purpose of the study is to develop a method for evaluating the plastic properties of nano-films in the large strain range. In this study, a stress concentrated region is intentionally created in a freestanding 500 nm-thick Cu film by introducing a notch having an appropriate radius of curvature. The local plastic deformation near the notch root is then qualitatively evaluated by a digital image correlation (DIC) method. The results show that the method can evaluate the local strain field ahead of the notch root in the large strain range up to about 4%.

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