In order to clarify the effect of the hydrogen environment on the slip behavior of a low carbon steel JIS S10C, fully reversed bending tests were carried out in hydrogen environment and in nitrogen environment. The main obtained result is as follows. The slip band continued developing over the 10^7 cycles in hydrogen environment. More crystal grains had slipped in hydrogen environment than in nitrogen environment after the fatigue test. This shows that the hydrogen environment prevented slip development from stopping. In order to compare the slip of each crystal grains microscopically in hydrogen environment with nitrogen environment, each crystal orientation is identified through EBSD analysis. The active slip system and Schmid factor of that identified through EBSD analysis and SEM image is also used to observe the slip.

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Fatigue crack growth behavior of a V and Mo added carbon steel was investigated in 0.1-90 MPa hydrogen gas at room temperature. The carbon steel was annealed, normalized, and quenched and tempered. Fatigue crack growth rates in 0.1-90 MPa hydrogen gas of these three steels were accelerated, compared with those in air. However, carbides of V and Mo limited the accelerations of crack growth rates. It was found that V and Mo addition is useful to develop hydrogen fatigue resistant carbon steel for hydrogen pipe lines.

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Low-and high-cycle fatigue properties of quenched and tempered SCM435 steel were investigated at R=-1 in 0.7 MPa H_2 gas, 0.1 MPa N_2 gas and air using round specimens with a small artificial hole (d=100 μm). At σ_a=500 MPa (low-cycle fatigue), N_f at 2 Hz in N_2 and air was almost the same. N_f at 2 Hz and 0.2 Hz in H_2 was shorter than N_f at 2 Hz in N_2 and air. However, N_f at 0.02 Hz in H_2 was almost the same as N_f in N_2 and air. That is, N_f is the shortest at f=0.2 Hz in H_2. At σ_a=300 MPa〜400 MPa (high-cycle fatigue), N_f at 20 Hz in H_2 and N_2 was longer than N_f at 20 Hz in air. In addition, calculating strain intensity factor range ΔK_ε by cyclic stress-strain curve, the da/dN-ΔK_ε curve for short crack obtained by round bar specimens with a small artificial hole at σ_a=500 MPa was coincident with the da/dN-ΔK_ε for long crack obtained by CT specimens.

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To ensure safely use of hydrogen utilization machines after large earthquakes, the effects of multiple overloads and hydrogen on high-cycle fatigue strength of notched specimens were studied. The materials were SUS304 and SUS316L. For both materials, the fatigue strength was significantly reduced by multiple overloads. The cause was small cracks formed by the overloads. In SUS304, the reduction of fatigue strength was enhanced by hydrogen. The cause of the enhanced reduction was the acceleration of propagation of the small cracks. In SUS316L, there was no enhanced reduction. A prediction method of the fatigue strength under the effects of hydrogen and multiple overloads was proposed through the evaluations of the crack propagation using plastic strain range and the fatigue limit related to the crack length.

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In order to investigate the extremely slow fatigue crack propagation characteristics of JIS SCM440 CT specimen in 9MPa hydrogen gas environment, ΔK decreasing test by in-situ observation with microscope camera were carried out. Fatigue crack growth rate in hydrogen gas did not show saturating behavior but in air showed saturating behavior clearly. In addition, the fatigue crack growth rate in hydrogen gas showed oscillating phenomenon in the extremely low late region. The fatigue crack in hydrogen gas showed sudden increase in growth by coalescing with a new micro-crack initiated in front of crack tip. Fractographic analysis showed the existence of intergranular facets at the micro-crack. Intergranular facets are seen on the fracture surface tested in hydrogen gas, though the sizes and the area fraction decreases with decreasing the ΔK, while there is no facets in helium and in air in the extremely low late region.

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Gigacycle fatigue properties of a storage cylinder in hydrogen station, which had been subjected to 4 years verification tests, was examined in both longitudinal and circumferential directions. The storage cylinder was made of SCM435 steel. Fatigue tests were carried out on hydrogen-charged and uncharged specimens by using ultrasonic and servo-hydraulic fatigue testings. In the uncharged specimens, only surface fracture occuned in both directions. On the other hand, the hydrogen-charged specimens showed internal fracture and degradation of fatigue strength. The crack initiation sites of internal fracture were different in the two directions: globular Al_2O_3 and slender MnS inclusions in the longitudinal and circumferential directions, respectively. The fatigue strength of the hydrogen-charged specimens was lower in the circumferential direction than in the longitudinal direction, while the difference was small.

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This study is about Shape of Crater and Ejecta Induced by Oblique Hypervelocity Impact. Target is aluminum alloys A6061-T6. Projectile is polycarbonate. Impact angle is 0, 15, 22.5, 30, 45 and 60 degrees. About the crater, we study visual observation, sectional shape, depth and so on. On the other hand about ejecta, we study visual observation, ejecta form, scattering angles and so on. At the result of this study, both the crater and the ejecta form are different depending on impact angle. For instance, depth of crater suddenly become shallow over 30 degrees, ejecta form is thinner and thinner as larger angles.

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This paper describes about evaluation of ejecta emitted from surface of spacecraft materials, where ejecta is defined as fragments generated from space structures surfaces due to the impact of debris at hypervelocity. Since ejecta can cause great damage to a spacecraft, it is of primary importance to better understand the space debris environment in order to design safer spacecrafts. To reach this goal computational models have been developed so far. Unfortunately, regarding the impact flux, the models present important dissimilarities for debris sizes ranging from 100 μm and 1 mm. To make up this lack of data on ejecta it is thereby necessary to develop ground experiments. However there is no common test procedure and each facility has its own way to proceed, which makes difficult to compare results between the different facilities. To overcome this issue, this study suggests and establishes a possible test procedure applicable by all facilities, which will be then used for the creation of an international standard.

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The Herbert hardness tester is a typical pendulum type one. The hardness is measured using swinging angle of the pendulum on the specimen. However, the Herbert hardness tester is not common in hardness measurement in the present. We have manufactured Habara-type Herbert pendulum hardness tester and improved measurement system of the swing angle. In our previous study, the swing angle was measured using one laser displacement meter, but this measurement system could not measure it exactly. We used two laser displacement meters to measure the swing angle exactly. The hardnesses were measured by Habara-type Herbert pendulum hardness tester with modified measurement system and Vickers hardness tester. Damping hardness obtained by modified measurement system was found correlate linearly with Vickers hardness. Therefore, the damping hardness is reasonable value. The modified measurement system provides accurate measurement using the Habara-type Herbert pendulum hardness tester.

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In this paper, we present a piece of effective online simulation technology that can be used to design various plastic forming processes. In particular, we have proposed a multi-stage simulation system called QRIS, which enables quick and accurate estimation of the foaming loads involved in each process. We then investigated its potential applications to processing with ultrasonic vibration applied on tools or materials, which is used in many technical fields nowadays to prevent cracking and adhesion by reducing the forming load. First, Common Platform Model (CPM) was constructed based on theoretical understanding of relations between processing conditions and phenomena developed from previous works. Then we carried out multiple simulations to test the accuracy and reliability of the model. The findings from these simulations prove our theoretical models and should form a suitable basis for verifying efficiency throughout the paper.

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In this paper, we present a piece of effective online simulation technology that can be used to design various plastic forming processes. In particular, we have proposed a multi-stage simulation system called QRIS, which enables quick and accurate estimation of the foaming loads involved in each process. We then investigated its potential applications to processing with ultrasonic vibration applied on tools or materials, which is used in many technical fields nowadays to prevent cracking and adhesion by reducing the forming load. First, Common Platform Model (CPM) was constructed based on theoretical understanding of relations between processing conditions and phenomena developed from previous works. Then we carried out multiple simulations to test the accuracy and reliability of the model. The findings from these simulations prove our theoretical models and should form a suitable basis for verifying efficiency throughout the paper.

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The final aim of this study is to come up with a new method which supersedes conventional means. It should be superior and can be used flexibly for visualization of strain, comparing to the previous ones. Therefore, we attempted to visualize the strain by using three various types of films, which are piezoelectric film (PVDF), polyimide film (PI) and temperature-sensitive liquid crystal micro capsule film (TLCM). The PVDF can output strong voltage for repeated load. The PI generates heat in regarded to the voltage. And then, TCLM can recognize the heat visually. The PVDF is to the PI what demand is to supply. The TCLM is used so as to visualize the thermal field of the PI. Finally, we acquired valid consequences by the way of complex the above films through experiments, so that we'd like to address regarding this study

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A new highly sensitive strain measurement method has been developed by applying the change of the electronic conductivity of CNTs. Multi-walled CNTs were dispersed in various kinds of resins such as epoxy, polycarbonate, and polyisoprene to form a thin film which can be easily attached to rounded surfaces. The length and diameter of the CNTs were about 5 μm and 50 nm, respectively. One of the base materials of resin employed was polycarbonate and the volumetric concentration of CNT dispersed was about 11.5%. The thickness of the film was about 500 μm. Uni-axial strain was applied to the CNT-dispersed resin by applying a 4 point bending method, and the change of the electric resistance was measured. The range of the applied strain was from -0.025% to 0.025%. The electric resistance changed almost linearly with the applied strain. The ratio of the resistance change under the tensile strain was about 400%/%strain and that under the compressive strain was about 150%/%strain. Two-dimensional strain fields were evaluated by using finely area-arrayed CNT-dispersed resin made by MEMS technology with spatial resolution of 50 μm.

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Carbon nanotube(CNT)-dispersed resin is expected to be a highly sensitive and remote strain sensor without interconnections. Application of microwave showed the possibility of the non-contact measurement of the change of electrical impedance of the resin under dynamic load by measuring the change of its reflectivity obtained from the surface of the resin. A theoretical method to estimate the change of the intensity of the microwave reflected from the resin was discussed based on the microwave theory. The change of the reflectance under tensile strain of 11% was calculated by the method using the measured change of the impedance of the resin under the frequency range between 1Hz and 10MHz. As a result, both real and imaginary parts of the impedance changed drastically with applied strain.

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From a traffic safety point of view, there is an urgent need for intelligent tires which can optimize braking control by estimating the slip ratio and friction coefficient between road surface and tire. This study develops a concurrent method for estimating the frictional and vertical loads applied to the tires from the measured strain data when both loads change. The method decomposes the measured circumferential strain to the frictional and vertical strain components using their symmetrical and anti-symmetrical characteristics. FEM analysis is used for simulating tire deformation under various wheel loads and braking torques. When the estimated and true applied loads were compared, it was confirmed that the vertical and frictional loads can be estimated independently from the circumferential strain with sufficient accuracy.

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This research is about method for evaluation of probability of failure to adopt the statistical unsupervised damage diagnostic for the risk based maintenance. By the diagnostic method, occurrence of the damage is diagnosed by statistical evaluation of the change of relation between measurement of several sensors. Therefore, diagnosis is conducted by means of only intact data and doesn't require information about the damaged condition. Generally, evaluation of probability of failure for the static equipment is conducted by the progress prediction of the damage based on the hazard data base. However, about the non static equipment, since the damage mode is not limited to predictable damage like corrosion, a lot of damage is caused accidentally. So evaluation of the reliability just from the prediction of the damage is difficult. Therefore, for the non static equipment, reliability evaluation based on the monitoring data is effective. Then in this research, the method to evaluate the probability of failure from the proposed damage diagnostic method is proposed and the validity of the method is experimentally confirmed.

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Strain range controlled low-cycle fatigue tests were conducted using ultrasonic method in order to compare the state of the damage and the ultrasonic response of the STS410 and SUS316NG, and clarify the effectiveness in STS410 of this measuring method and clarify the range of frequency in which fatigue damage can be detectable using the ultrasonic back reflection. It was clarified that for the STS410 the crack growth start can be predicted according to the ultrasonic back-reflection intensity. An applicable limit in frequency is considered to exist between 20MHz and 50MHz for the present detection condition. This result can be used to predict the remaining life before the onset of crack growth within the plastic strain range used in this study and contributes the safety.

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In the operation of electric power plant, it is necessary to understand the condition of the pipe quantitatively. The purpose is to prevent the accident caused of the wall thinning portion clue to erosion or corrosion. The thickness of the pipe is partially measured with the ultrasonic thickness gage now. However, it is difficult to investigate the wall thinning portion in the pipe quantitatively without confirming it beforehand. In this study, to identify the location of thinning for the purpose, the ultrasonic testing system using the guided wave was developed, that was able to investigate partially the wall thinning portion of all aspects of pipe to be inspected at a time. The Ultrasonic system that developed was applied to the actual pipe of the power plant. Sensitivity has been improved from the result of the field test. In addition, the propagation control of the guided wave was enabled. As a Result, the range of detection is expanded more than traditional system and the detection accuracy of thinning has been improved. An efficient pipe investigation becomes possible because it widely understand the condition of the pipe by using this system. The reliability improvement of facilities and the reduction of maintenance and repairs are expected to be attempted.

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Up to date, the non-destructive testing (NDT) is mainly realized by using ultrasonic inspection, X-ray inspection, eddy-current testing and magnetic-particle testing, etc. These inspection methods have high accuracy and reliability. However, they also have some disadvantages. For instance, they usually take a long time to finish the inspection process because their inspection area is relatively narrow at one time. To overcome this demerit, the damage inspection techniques with Lamb waves which can detect a wide area due to their long-distance propagation ability are actively studied in recent years. In the present work, based on an inverse algorithm, a tomographic reconstruction technique of damage image, e.g., the area and shape of a damage, by using the amplitude decrease of the transmitted Lamb wave through the damage, is proposed. From the obtained experimental results, the validity of the proposed method for reconstructing the damage image is verified. This method can be also applicable to the case where multiple damages exist in the inspected area.

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We have developed the constant phase focusing method in non contact air coupled ultrasonic testing for circumferential scanning of pipes with the ultra high power square burst waves. This method is available for transmitting & receiving of sensitive guided waves in pipes. This paper describes the constant phase focusing method using a focusing probe in optimum frequency, incident angle and probe's selection & design.

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Ultrasonic flaw detection and sizing are important issues for ensuring structural reliability of industrial plants. The ultrasonic phased array technique is one of the most effective tools for visualizing the flaws in structural components. However, in the case of flaw size measurement, only an A-scope signal is used for calculation usually. On the other hand, the Time-of-Flight Diffraction method is known as the most accurate flaw sizing method. However, TOFD method is applicable only if the flaw exists on the perpendicular bisector of the ultrasonic probe pair. In this study, new flaw sizing method by using many ultrasonic oscillators was introduced. Through this process, dilution of precision (DOP) was introduced to evaluate measurement error of flaw tip position. By using numerical calculation, the relationship between the DOP and the flaw tip position measurement accuracy was investigated.

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This paper describes Acoustic Emission (AE) measurement used to assess the fatigue life and failure mode of piping with local wall thinning subjected to seismic loading. Local wall thinning by erosion/corrosion was simulated by machined pipe wall tinning. Low cycle fatigue tests for the pipes were then carried out. Furthermore, AE method during low cycle fatigue tests was employed to evaluate the crack initiation and propagation. As a result, AE was detected when the tensile stress applied to the tip of the crack, and was drastically incased at the fatigue life cycle. Based on Miner's law, authors discussed about AE behaviors due to fatigue damage.

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The present another proposed the passive electric potential CT method and the supersonic wave pulse echo method using smart layer for detecting and monitoring defects and cracks. The passive electric potential CT method uses a piezoelectric film in the smart layer as a strain sensor. The supersonic pulse reflection method uses the piezoelectric film as a supersonic wave transducer. In the present study the supersonic wave multiple electrodes pulse echo method emitting and receiving pulse echo on electrodes placed on the piezoelectric film is proposed. The applicability of the method to the identification of vertical cracks was experimentally examined. From the time-of-flight of pulse echo emitted from an electrode and received on another electrode an oval is drawn, which is tangential to crack surface. It was found that the obtained ovals intersected at several points. The positions of the intersection agreed well with those of crack tips, indicating the effectiveness of the present method.

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For the design of mechanical structures, the fatigue limit is indispensable. Therefore, it has been developed the simple evaluation method with thermography. In this method, the temperature change can be measured for the specimen under cyclic load, and the fatigue limit is corresponding to the inflection point the temperature starts to rise rapidly. It is largely unclear the mechanism of the between fatigue limit and temperature rise, though this method has been studied widely. In this study, we aim to clarify these mechanisms, we perform to investigate the effects of various factors influencing the temperature rise.

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In recent years, fatigue limit estimation method based on energy dissipation measured by infrared thermography is getting an increasing attention. In this method, temperature change due to irreversible energy dissipation during one loading cycle is measured for different levels of applied amplitude. Obtained relationship between temperature change and stress amplitude shows a significant inflection at certain stress level where temperature change due to energy dissipation shows steep increase. It is known that this stress level coincides with fatigue limit. However, mechanism of energy dissipation in relation to fatigue damage initiation has not been investigated yet. In this study, fatigue test is conducted for 304 stainless steel specimen. Temperature change due to dissipated energy, martensite fraction and strain are continuously measured to discuss energy dissipation mechanism related to plastic strain and transformation of microstructure during fatigue test.

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In recent years, fatigue limit estimation method based on energy dissipation measured by infrared thermography is getting an increasing attention. In this method, temperature change due to irreversible energy dissipation during one loading cycle is measured for different levels of applied stress amplitude. Obtained relationship between temperature change and stress amplitude shows a significant inflection at certain stress level where temperature change due to energy dissipation shows steep increase. It is known that this stress level coincides with fatigue limit. In this study, measurement conditions for appropriate fatigue limit determination based on the energy dissipation are discussed in conjunction with (i) required number of loading cycles in each stress level, (ii) representative value in measurement area, and (iii) influence of loading history and fatigue damage accumulation.

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In this study, the equivalent elastic constants for the out-of-plane deformation of unsymmetrical triangle honeycomb were studied theoretically based on the equivalence of deformation energy. A honeycomb composed of unsymmetrical cells is anisotropic. In this case, the deformation of the honeycomb can be calculated by considering two equivalent elastic constants which are not considered at an analysis of orthotropic. Also, the accuracy of the equivalent elastic constants obtained in this theoretical method on the equivalence of deformation energy is found to be high in comparison with numerical result. It means that the equivalent elastic constants for the out-of-plane deformation of any periodic structure can be obtained in this theoretical method.

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When an Elastica with variable stiffness is pushed by a rigid plane, the Elastica is buckled in the contact region. We model this buckling phenomenon as a free boundary problem for an arch made of a variable-pitch strand, taking into account the variable stiffness as a macroscopic structural inhomogeneity. By using a continuation scheme we solve the problem numerically and determine the critical buckling load of the arch for several types of the bending stiffness distribution.

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The mechanical and thermal properties of polymer composite materials system reinforced with glassy micro balloons are investigated in temperature conditions. Its dispersion is micro size of glassy spherical hollow shells of "Sirasu Balloon" and the matrix is epoxy resin. Developed composites are a kind of micro porous materials with low density. From the experimental results, mechanical behaviors of the composites were clarified, and the effects of material properties and configurations on the mechanical properties of composites were discussed from the viewpoint of micromechanical study. A homogenization theory with multi-scale analytical method has been applied in order to evaluate their thermal properties. Using a model of micro porous materials and setting property of each material, numerical calculation was performed. Analytical results for the mechanical behavior made a good agreement with experimental results of the composites in temperature conditions and thermal conductivity of the composites was estimated.

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In the previous paper, the authors has dealt with the problem of adhesive joint under tension, and the effect of the adhesive thickness and material combinations on the strength of adhesive joint have been discussed. Using the FEM, it is has been explained explicitly that the strength of adhesive joint decreases with increasing of adhesive thickness under arbitrary material combinations. In this paper, the problem of adhesive joint under bending will be discussed using the FEM. Similarly, the effect of adhesive thickness and material combinations on the strength of adhesive joint will also be discussed. Comparing the results of tension and bending for the adhesive joint, the intensity of singular stress for the bending is larger than the intensity of singular stress for the tension for the most material combinations, although the intensity of singular stress for the bending is always smaller than intensity of singular stress for the tension for a bonded strip.

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This paper deals with the analysis of the thermal stress intensity factor for interfacial crack in dissimilar materials subjected to uniform change of temperature by using the finite element method. In the present method, the stress values at the crack tip calculated by FEM are used under the same mesh pattern and the stress intensity factors are evaluated from the ratio of stress values at the crack-tip-node between a given and a reference problems. This method is based on the fact that the singular stress field near the interface crack tip is controlled by the stress values at the crack tip calculated by FEM. As the reference problems, a single interface crack in an infinite bi-material plate subjected to tension and shear is selected in this study. The accuracy of the present analysis is verified by the comparing the present results with the results obtained by difference mesh sizes and other researches. The calculation shows that the present method has the sufficient accuracy in the interface crack problems under thermal stress.

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The beam theory which takes into consideration varying thickness due to deformation was developed to accurately analyze bending behavior of a thick beam. The displacement model in the theory can express not only transverse shear deformation but also normal one by using a shape function of conventional transverse shear deformation theories, such as third-order shear deformation theory. Bending problem of simply-supported thick beams was analyzed to confirm the validity of the new beam theory. The deflection and stress components given by the theory agreed with the solutions evaluated by the two-dimensional elasticity even for a very thick beam. Therefore, it was clarified that the theory can express deformation behaviors of thick beams with varying thickness.

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This study is concerned with a magneto-thermo-elastic problem of a conducting beam in an external magnetic field which varies sinusoidally in time. Analytical solutions of eddy currents induced in the beam are derived on the basis of a theory of the quasi-stationary current. One-dimensional transient temperature change produced by the eddy current loss is derived by means of the Green's function method. The deflection and stress in the beam under the condition of simply supported edges are derived on the basis of Bemolli-Euler beam theory. The effect of a frequency in a sinusoidal change in time of the external magnetic field on behaviors of eddy current loss, temperature change, deflection and stress is examined. The skin effect with an increase in a frequency of the external magnetic field on the transient thermo-elastic behavior in the beam is discussed.

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The in-phase and 90deg out-of-phase straining axial-torsional low-cycle fatigue tests were conducted on Mod.9Cr-1Mo steel at 823K under the PP-type strain waveform, and it was examined whether or not the equivalent plastic strain range proposed by the author and his colleagues to estimate the effect of nonproportional loading in case of SUS304 and 316LC steels can be applied to Mod.9Cr-lMo steel. As the results, it was found that the observed nonproportional loading effects were little in case of Mod.9Cr-1Mo steel and not only the proposed equivalent plastic strain range but also the von Mises plastic strain range and the Brown & Miller's equivalent shear strain amplitude. can well estimate the 90deg out-of-phase straining axial-torsional PP test lives of the material.

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This study discusses multiaxial low cycle fatigue life of Mod. 9Cr-1Mo steel under proportional and non-proportional loadings at room and high temperatures. Components and structures like pressure vessels and high temperature exchangers undergo multiaxial low cycle fatigue damage. For Mod. 9Cr-1Mo steel, a few studies on multiaxial fatigue has been performed, so examination of deformation and life behavior under multiaxial fatigue should be needed. In this study, strain controlled multiaxial low cycle fatigue tests under a push-pull, a reversed torsion and circle straining tests at room temperature and 823K were carried out using a hollow cylinder specimen of Mod. 9Cr-1Mo steel. Decrease in failure lives under non-proportional loading was remarkable. Failure life estimation and deformation and failure behaviors were discussed.

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This study discusses creep-fatigue life of type F82H steel used in a blanket structure of a DEMO fusion reactor under uniaxial and multiaxial loadings at 823K. Strain controlled creep-fatigue tests were carried out using a hollow cylinder specimen. Three kinds of loading paths were employed; they were push-pull straining, reversed torsion straining and circular straining. The former two were proportional loadings and the latter one was a non-proportional loading where principal direction of stress and strain was changed in a cycle. Four kinds of waveforms (PP, PC, CP and CC) were employed in order to evaluate an effect of strain rate on the lives. F82H showed that failure life was affected by multiaxial strain path and reduction in the life due to non-proportional straining could be seen. However, the effect of strain rate on the lives was small.

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Fatigue crack growth tests under multiaxial stress conditions were conducted at elevated temperature. Cyclic tension and torsion were applied to the thin-walled cylindrical specimens of SUS 304 stainless steel. By using DC electrical potential drop (PD) method, fatigue crack growth rate was quantified. Under multiaxial stress 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, τ_<max>. Using the crack length projected to the φ-direction and the direction of τ_<max>, fatigue crack growth rates were evaluated by the corresponding stress intensity ranges, ΔK_<Ib> and ΔK_<Iic>, respectively. The characteristics of both type of fatigue crack were discussed.

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In this study, biaxial thermo-mechanical fatigue (TMF) tests simulating actual blade loading condition have been carried out using a directionally solidified super alloy which is typically used in 1300C class gas turbine blades. Fatigue lives under biaxial TMF life could not be correlated with Mises equivalent strain range. An equivalent shear strain range for the Ni based DS superalloy was derived based on Γ-plane theory, and the biaxial TMF life was well correlated with the equivalent shear strain range. It was found that fatigue life was reduced to 1/5 by introducing 6 minutes strain hold time at the maximum temperature. This life reduction may be occurred due to increasing of tensile stress during strain hold period.

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There are several types of fatigue testing machines under multiaxial loading. Each type of testing machine has its own characteristic, but most of multiaxial fatigue studies have been performed by a using push-pull and reversed torsion fatigue testing machine with a hollow cylinder specimen. This testing machine can perform multiaxial fatigue tests under not only proportional loading but also non-proportional loading where principal directions of stress and strain are changed in a cycle. However, the principal strain ratio range performable is -1&le;ε_3/ε_1&le;-v, where ε_1 and ε_3 are the maximum and the minimum principal strains and v Poisson's ratio. Since structural components under service loading undergo wider principal strain ratios, fatigue testing machines which can perform the wider multiaxial stress and strain states are necessary to evaluate the multiaxial fatigue damage precisely. This study developed two types of fatigue testing machines for multiaxial fatigue. One is a biaxial testing machine using a cruciform specimen. The other one is a testing machine using the hollow cylinder specimen added combining push-pull and reversed torsion loadings with cyclic internal and external pressures.

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Low cycle fatigue tests have been made on elbow. It was found that universal slope method give non-conservative fatigue lives. Revised universal slope method was proposed which take into consider with multi-axial stress condition on true fracture strain using Miyazaki's equation. The method gave good prediction with experimental fatigue lives.

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This study discusses multiaxial low cycle fatigue (MLCF) life of SUS316 stainless steel under proportional and non-proportional loadings at room temperature. Strain controlled MLCF tests were carried out using SUS316 hollow cylinder specimen with 6 types of strain paths. Reduction in failure lives were observed accompanying by additional hardening due to non-proportional straining. However, mean strain effect under T-shaped strainings, where 1, 10 or 100 cycles of reversed straining were applied with tensile constant straining, was reduced with increasing cycles of reversed torsion straining.

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This study discussed surface crack and microstructure of Mod. 9Cr-1Mo steel fatigued under multiaxial loadings. Strain controlled multiaxial low cycle fatigue tests were carried out using a hollow cylinder specimen including interruption tests. Strain paths employed were a push-pull straining and circle straining. The latter is the non-proportional loading test where axial and shear strains have 90 degree phase difference and principal directions of stress and strain are changed in a cycle. Surface cracks and microstructures fatigued specimens were observed by a digital microscope and a transmission electron microscope (TEM) in order to investigate mechanisms of cyclic deformation, failure and reduction in life due to non-proportional loading.

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This paper presents the nonproportional low cycle fatigue life for oxygen-free high conductivity copper. Strain controlled tension-torsion low cycle fatigue tests were performed using hollow cylinder specimens under four strain paths: push-pull, torsion, combined tension-torsion and 90 deg. out-of-phase strain paths. Fatigue lives under circular path were smaller than those under the other three strain paths at the same Mises equivalent strain ranges. The difference in fatigue lives was discussed in relation to the additional hardening effect in nonproportional loading. Applicability of maximum principal strain and nonproportional strain was discussed to evaluate multiaxial low cycle fatigue lives.

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It is recognized that flaking-type failure due to contact fatigue is closely related to the growth of the shear-mode (Modes II and III) fatigue crack. In our research group, it is demonstrated that a shear mode fatigue crack can be reproduced for the cylindrical specimens by applying the cyclic torsion in the presence of the static axial compressive stress. However, a biaxial servo-hydraulic fatigue testing machine used is quite expensive to purchase and costly to maintain. Low testing speed (〜10 Hz) of the testing machine further aggravates the situation. As a result, study on shear mode fatigue crack growth is still in nascent stage. To overcome those difficulties, we have developed a high performance and cost-effective testing machine to reproduce the shear mode fatigue crack growth by improving the available resonance-type torsion fatigue testing machine. The primary advantage of using the resonance-type torsion fatigue testing machine is cost-efficiency. In addition, the testing speed can be effectively improved in comparison with that of a biaxial servo-hydraulic fatigue testing machine.

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Parylene C is an inert, hydrophobic, flexible and biocompatible polymer coating material, which has recently found broad MEMS and BioMEMS applications including microstructures, micro sensors and actuators. As a result, many researches have been conducted by focusing on the utilization of Parylene C thin films. Little attention, however, was paid to and rare was known about the mechanical properties of the thin films that may subject to severe tension, bending, twisting or the combination of these loading, especially in biomedical implants in which strength reliability must be secured during a reasonable lifetime. The objective of the present study, therefore, is to investigate the tensile properties of Parylene C thin films fabricated by micromachining process in the range of thickness from submicron to tens of microns. The effect of sample thickness is discussed.

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This paper deals with influence of foil thickness on mechanical property of copper foil. Tensile tests were carried out for annealed Cu foils. The influence of foil thickness on the deformation, tensile strength and fracture morphology were investigated. In order to examine the mechanical property of Cu foils, the thickness of Cu foils ranges from 5 to 2000 microns and the average grain size of each specimen is 20 microns. The tensile strength of the foil thickness of 5 and 10 microns were lower than that of thicker foil. While the chisel-point fracture occurs if the grain size is larger than foil thickness, the intergranular fracture is observed if the grain size is smaller than foil thickness. The results are explained on the basis of texture differences; the deformation is constrained by the other nearby grains and the number of grain in the thickness direction decreases with increasing foil thickness. In the case of thickness 5 and 10 microns, only one grain exists through thickness direction. Therefore, the mechanical properties of the thinner foils are affected by foil thickness.

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In this paper, surface roughness of stainless steel SUS316NG used for piping systems of nuclear power plants is measured after the stainless steel is subjected to a several amounts of plastic deformation up to 18%. The two types of surface roughness such as line(1D) roughness and area(2D) roughness are measured by using the 3D color laser microscope. The 2D roughness in a crystal is also measured. The measurements show that there is a difference in 1D roughness due to the location of measurements of the specimen after deformation, while the value of the 2D roughness does not vary due to the location. It can be also found that the 2D roughness is well proportional to the plastic deformation. The linear relationship between the 2D roughness and plastic deformation can be also seen in small strain range under a few percents, which suggests that a possibility to estimate the plastic deformation using measured surface roughness.

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In this study, at first, MD simulation is performed to clarify the effect of water contents on the distribution of density of molecular chains of PEM under uniaxial tension. It is found that the lower water contents the more remarkable change of the density of molecular chains of PEM, which may lead to a high possibility of the nonaffine movement of the physically entangled points in the molecular network. Continuously, a computational model, in which the development of the number of the physically entangled points is assumed to be a function of the relative humidity, is employed to discuss the effect of the water contents on the mechanical behavior of PEM under various loading condition.

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Heat exchangers such as charge air cooler can fail due to thermal strain. At that time, we can use FEA and estimate loading stress. But it is not possible modeling of whole detailed structure for charge air cooler, because plate-fin structure of charge air cooler is complex. So, because plate-fin structure is periodic, homogenization method can be applied. There we focusing on fin shape, we try homogenization analysis for the various shape of fin (real and designed shape), and compare experiment. As a result, real shape of fin is consistent with experiment. Thus, when we apply homogenization method for plate-fin structure, we should use real shape of fin and make the whole product model.

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