Stress redistribution locus (SRL) method has been proposed to provide a reasonable estimate of inelastic behavior under elevated temperatures employing both the elastic Finite Element (FE) analysis and a unique hyperbolic curve: ε={1/σ+(κ-1)σ}/κ, where ε and σ show dimensionless equivalent strain and stress normalized by elastic ones obtained in the elastic FE analysis. In order to investigate applicability of the SRL method for elastic-plastic components, low cycle fatigue tests were conducted employing a smooth and four kinds of circumferentially notched bars. The number of cycles to crack initiation was compared with the one estimated by the SRL method. When an adequate elastic region remained inside the notch root, the crack initiation life could be well predicted by the SRL method. However when a ratio of the plastic area in the notch root section occupied over about 0.3, the equivalent strain range on the surface of the notch root calculated by the SRL method became to be smaller than the one by the detailed inelastic FE analysis. On this occasion the crack initiation life calculated by the SRL method would be overestimated.

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In this paper, the elastoplastic collapse of a cylindrical tube subjected to pure bending is studied by using the finite element method. There exist two types of collapse: a collapse due to buckling at the compression side and a collapse due to flattening of the cross-section. In the flattening collapse, the maximum bending moment is controlled by the flattening rate of the tube cross-section. For a short tube, the boundary condition of the fixed walls at the both ends prevents the flattening development. A theoretical prediction method of the flattening rate and the maximum bending moment of cylindrical tubes subjected to pure bending is proposed, in which the effect of the tube length is taken into account. In the method the flattening is simulated by a deflection problem of a beam based on distributed springs. The validity of the proposed method is verified by numerical results of FEM.

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Novel cohesive element which can deal with non-self-similar crack growth under mixed-mode II and III failure condition is proposed. The local coordinate system based on the crack front direction is determined in terms of relative displacement of the cohesive elements. Traction-relative displacement relation of the element is determined as a function of mode components calculated on the local coordinate system. This formulation allows us to simulate delamination growth when the non-self-similar crack growth occurs and the fracture toughness depends on the mode ratio. The numerical examples revealed that the crack growth strongly depends on its history when the mode II and III fracture toughness is different and the present formulation is valid even for the simulation of such history dependent crack growth.

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Recent earth environment problem is accelerating rapid popularization of hybrid or electric vehicles replacing conventional vehicles powered by fossil fuels. Such electric vehicles don't need exhaust pipes and power train system like propeller shaft under the floor and the floor can be flattened. Flat floor may also contribute to crash safety and suitable structural material for this purpose will be required. In this paper authors studied optimal shape to improve energy absorption ability of truss core panel which are considered to use vehicle structure. Effective optimization technique especially for nonlinear problem, Radial Basis Function (RBF) network with Response Surface Method (RSM) is adopted in the paper and applied to optimize the shape of truss core panel. Energy absorption quantities for x, y, and z direction were treated as independent objectives and multi-objective optimization was performed. A commercial preprocessor HyperMorph is used for morphing, explicit FEM software LS-DYNA is used to solve crash analysis and LS-OPT is used to handle multiple jobs and optimization process. As the result, 7.1% of improvement for energy absorption for crash in x direction was achieved and Pareto curves for the objectives were obtained.

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High-velocity impact experiments were conducted on magnesium alloy plates at room and cryogenic temperature, 298K and 153K. An aluminum sphere with room temperature impinged at the target plate with its speed ranging from 0.5 to 1.7km/s in 100Pa air. The impact process was visualized by shadowgraph, and recorded with the ultra-high speed video camera. Results of the experiment was compared to results which were obtained from previous experiments for a thicker specimen. In addition, it was compared to experimental results from aluminum alloy specimens that our co-investigator presented in the past. As a result, the difference was found on the damage of debris cloud impingement. It was affected by bumper material, plate temperature and impact velocity. It is thought that the bumper performance of the magnesium alloy is better than aluminum alloy, because the damage of magnesium alloy was distributed more shallowly and more widely than that of aluminum alloy.

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A method that uses grain growth direction in copper foil to measure cyclic biaxial stress is examined in this paper. The grain growth direction is measured by image processing software after a cyclic bending-torsion test for various biaxial stress ratios is carried out. Peaks of the relative frequency distribution of the grain growth direction correspond well with the direction of maximum shearing stress, and the interval from one peak to another peak is almost 90°. These results mean that the grain growth direction is controlled by the maximum shearing stress. The principal stress is obtained with Mohr's stress circle and the peak of the curve obtained by approximating the relative frequency distribution. The number of grains necessary to measure the biaxial stress is estimated by a statistical approach. From this result, it is cleared that the area necessary for the principal stress measurement was only 9mm^2. This area is almost half of the area necessary for conventional method.

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ECT (Eddy Current Testing) and UT (Ultrasonic Testing) have been widely used for the non-destructive testing of metal structures. It is well known that these two techniques complement each other for crack sizing; ECT has a high capability of sizing of a surface breaking crack and UT is suitable for sizing of a sub-surface breaking crack in thick-wall structure. Based on these back-grounds, the authors have proposed a novel dual probe with simple structure that combining EMAT (Electromagnetic Acoustic Transducer) and EC (Eddy Current) probe. In this paper, the above dual probe is applied to monitoring of piping wall thinning in high temperature environment. For the purpose, the structure and components of the probe are discussed so that the present probe should withstand the operating temperature of up to 300 degrees C which corresponds to the operating temperature of boiling-water nuclear reactors. Finally, basic performance of the probe at high temperatures is investigated through experiment using an electric furnace.

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Crack propagation rate of SCM440H low alloy steel under long term varying load is enhanced by absorbed hydrogen. Substantial acceleration of crack propagation rate up to 100 times was observed. Macroscopic approach to examine the role of hydrogen on the acceleration was investigated by changing loading condition and charging condition. (1) The predominant fracture mode of hydrogen charged material showing acceleration was quasi cleavage. The application of stress prior to hydrogen charge prevented the quasi cleavage cracking in the following hydrogen-charged condition. This suggests that hydrogen restrained blunting of crack tip, which resulted in relatively higher stress state in hydrogen charged material. The higher stress state caused quasi cleavage and acceleration of crack propagation. (2) The crack opening displacement (COD) was measured on hydrogen charged material and uncharged material. COD was smaller in hydrogen charged material. The stress for the onset of non-linear deformation in stress-COD relation was higher in hydrogen charged material. These examinations suggested that the mechanistic role of hydrogen is to prevent the blunting of crack tip and bring about higher stress field near the crack tip.

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The effects of hydrogen on fatigue crack propagation behavior of short fatigue crack and crack closure behavior were studied using low alloy steel SCM440H. Fatigue crack propagation test using specimen with s a 50μm deep pre-crack was carried out at a frequency of 28.4Hz in air, vacuum and hydrogen gas. Hydrogen pre-charge was done by cathodic polarization method. The concentration of absorbed hydrogen was 0.83ppm in hydrogen charged specimen and 0.06ppm in uncharged specimen. The fatigue crack propagation rate of uncharged material was dependent on environment. The acceleration of fatigue crack propagation rate by absorbed hydrogen was about 2 to 5 times irrespective of environment. As a result, the fatigue crack propagation rate of hydrogen pre-charged material tested in air was the highest. The crack opening stress was higher in hydrogen gas and in vacuum compared with that in air. Fatigue crack propagation rate was summarized in two independent bands when plotted against effective stress intensity factor. This means that the effects of environment (vacuum, air and hydrogen) and stress ratio (R=-1, 0, 0.6) could be explained by crack closure phenomenon. However, the acceleration of crack propagation by absorbed hydrogen could not be explained only by crack closure phenomenon.

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Fatigue tests were conducted on specimens of ultrafine grained copper produced by equal channel angular pressing. The growth behavior of a major crack, which led to the final fracture of the specimen, was monitored successively. Propagation behavior of the crack was influenced by damaged zone ahead of the crack tip, and consequently different morphologies of the fracture surfaces developed, depending on the stress amplitude and crack length. The change in fatigue fracture surface morphologies was occurred from a change in crack growth mechanism and was qualitatively explained by considering the interrelation between grain size and the reversible plastic zone size at the crack tip.

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Several researchers have proposed some repair methods for damaged machines. It is well known that the stop drilling hole is useful and practical method for fatigue damages. Moreover, the relaxation effect of the stress concentration can be increased by adding notches, holes and so on to the stop drilling holes. The stress concentration of the crack with the stop drilling hole can be relaxed by adding two holes near the crack tip as the holes face with each other symmetrically. Then, it has been reported that the additional holes are effective in the fatigue crack extension. However, the stop drilling hole and the additional hole suitable for repairing the fatigue crack are not clarified. In this paper, the fatigue tests of the cracked plates with the stop drilling holes and additional holes were carried out on the low carbon steel S45C changing spatial and dimensional relations between the stop drilling hole and the additional holes. The influences of the relations on the fatigue life extension are examined.

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Effects of loading rate on damage behavior in a pig liver loaded in compression were experimentally investigated. First, we developed a macroscopic damage model of liver cells or hepatocytes. Next, microscopic damage mechanism at the cell level was discussed through in-situ observation. Yield stress and strain were decreased with increasing strain rate. This behavior was ascribed to difference in pressure among individual liver components. The stress in a liver specimen subjected to a constant strain completely disappears after a certain period of time. For low strain rate, all the cells can endure high yield stress and strain because there is enough time for the individual cells to equilibrate the pressure. In contrast, for high strain rate, the yield stress and strain, became lower since the cells cannot equilibrate the pressure due to limited intercellular blood flow during a short time. An interlobular connective tissue (Glisson's sheath) of a hepatic lobule was not easily damaged in the compressive field as it is stronger than the internal tissue. Consequently, the first failure occurred in the weakest central vein.

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We clarified experimentally electrical and mechanical properties of SMA (Shape; Memory Alloy) in diameter 0.2mm and SMP (Shape Memory Polymer) in thickness 1.15mm. In addition, SMC (Shape Memory Composite) composed of these SMA and SMP, was also investigated to clarify the electrical and mechanical properties required to actuators. Main results obtained in this study are as follows; (1) When SMA was heated electrically over 0.4A, recovery time until the original figure was under 5 seconds. (2) When SMC was heated electrically over 0.3A, the surface temperature of SMC reached approximately T_g after 120 seconds. (3) We confirmed that application of 0.4A and 120 seconds to SMC was the most suitable condition as an actuator controlled electrically.

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An Analytical model for the mechanical behavior of a bolted joint subjected to a transverse load has been theoretically formulated. This paper focuses on the modeling of self-loosening that is based on the analytical model of the transverse load-displacement relation proposed in our previous paper. While the mechanical behavior of a bolted joint before complete bearing-surface slip was modeled in the previous paper, slip displacement due to complete bearing-surface slip is added in this paper in order to model self-loosening due to both micro and complete bearing-surface slip. In the case of complete bearing-surface slip, slip displacement in the circumferential direction on the thread and bearing surfaces is modeled to be proportional to the torsion torque accumulated during the process of micro bearing-surface slip. From the loosening rotation angle, which is defined as the rotation angle of the bearing surface, and the axial-direction stiffness of the bolted joint, the decrease in bolt tension is calculated. We applied the proposed model to an M16 bolted joint and confirmed that the model is capable of representing self-loosening behavior due to both complete and micro bearing-surface slip. In addition, we show that the model is able to predict the transition from micro to complete bearing-surface slip and the change in loosening rate caused by the decrease in bolt tension.

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Relationship between the notch strength ratio, defined as the notch tensile srtength to tensile strength ratio, and the critical strain ratio was investigated on the notched tensile specimens. Critical strain ratio is the ratio of critical strain below the notch tip at the notch tensile strength to the plastic strain at necking instability, which is equal to strain hardening exponent. Critical strain was obtained from measurements of Vickers hardness. Notch strength ratio increased simply with increasing critical strain ratio for the notched specimens with different notch acuity. Thus, the critical strain ratio could be considered to be a major parameter which characterizes the notch strength ratio as well as the stress increase rate of notched specimens in the force-elongation response.

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