The operating lifetime of the components made of a large-scale forged material, such as the power generating components in a thermal power plant, is influenced by the initiation of defects such as cracks. Peening is known to be effective for the improvement of fatigue strength and the prevention of the stress corrosion cracking initiation. Shot peening that generates compressive residual stress on the material surface is applied to the stress concentration region of the high-strength large-scale forged material in order to relax the tensile stress, prevents crack initiation and extends operation lifetime. To confirm the durability of the compressive residual stress generated by peening, the influence of thermal aging treatment on the compressive residual stress is evaluated. As a result, it is reported that compression is maintained though compressive residual stress relaxes. The purpose of this study is to develop evaluation method of the relaxation behavior of residual stress generated by shot peening and laser peening during actual plant operations. Shot peening and laser peening were performed on the specimens of Ni-base superalloy Alloy 706, which is used as the material of the discs of gas turbines, and the thermal aging treatment test was performed. It shows that the compressive residual stress decreases to an elastic limit after heating and then relaxes due to creep strain generation. It is found that residual stress was almost determined by the residual stress just after heating.

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The hygroscopicity of various aged hinoki wood building elements (Chamaecyparis obtusa) was evaluated from their isotherms. The data showed that the moisture content of new wood was higher than that of aged wood when equilibrated at the same humidity. By applying the Hailwood-Horrobin adsorption equations to the data for aged wood, we determined that the number of sorption sites per unit volume at low humidity decreased and that the aggregation of water at high humidity decreased.

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In this paper, numerical investigation was systematically performed using thermal elastic-plastic analysis to study the effect of welding conditions in embedded flaw repair technique, such as weld heat input, crack depth and thickness of structural member, on the welding-induced residual stress at repair welds of nuclear power plants. The stress intensity factor (SIF) was also estimated based on the calculated distribution of residual stress around the remaining crack within repair parts. Meanwhile, the essential variable of welding conditions described above was theoretically derived from welding thermal conduction theory as representative of the temperature distribution along the crack to conduct the unified evaluation on the relation between the residual stress and the SIF around the remaining crack and welding conditions. As the results, it was concluded that the residual stress and the SIF at the downside crack tip region could be arranged by a unified curve associated with the essential variable derived. Besides, the residual stress becomes compressive and the SIF becomes zero when the essential variable is smaller than approximately 1.5. Further investigation was numerically performed for multi-layer and multi-pass repair welding process to study the effect of weld pass sequence on the residual stress and the SIF around the remaining crack. Then, it was clarified that the appropriate weld pass sequence condition was dependent on value of the essential variable described above. With the right selection of weld pass sequence, the residual stress and the SIF after multi-layer and multi-pass repair welding is possible to be compressive and zero respectively even when the essential variable is vastly larger than approximately 1.5 to introduce the highly tensile stress at the downside crack tip region after single-pass repair welding. Thus, the methodology to improve structural soundness for preventive maintenance at repair welds of nuclear power plants was developed on the basis of the essential variables of welding heat input and pass sequence conditions in embedded flaw repair technique.

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Two-dimensional FE simulations on prediction of position of kink band formation for a single crystal of a Mg-based LPSO phase are performed using a dislocation-based crystal plasticity model. We take account of activities of basal, prismatic and 2nd-pyramidal slip systems and assume that the LPSO phase is simply composed of HCP lattices for simplicity. However, a HCP crystal such as Mg and the LPSO crystal are distinguished by magnitude of critical resolved shear stresses of the slip systems and elimination of deformation twins. In addition, to express crystal defects in the kink band within the framework of continuum mechanics, GN dislocation density, SS dislocation density and GN incompatibility (disclination density) are incorporated into the hardening rule. We carry out the FE simulation. First, we assign initial dislocation density homogeneously to a specimen used in the simulation. The result shows that a kink band is formed in the center of the specimen and distributions of densities of isolated dislocations, dislocation pairs and disclinations are appropriately expressed by the present models of crystal defects. Next, introducing a heterogeneity into the distribution of the initial dislocation density, we investigate the effects on kink deformation in terms of total elastic strain energy. As a result, the position of a kink band formation changes so that the energy is structurally minimized.

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Ultrasonic fatigue tests were performed on notched specimens of medium strength steel, 2.25Cr-1Mo, and the bolt specimens of high strength steel, SNB7, under mean stress application, which was enabled by our original loading device in house. Stress concentration factor, α, and nominal stress of the notched specimens were obtained by means of static and dynamic analyses of finite element method. For the notched specimen of 2.25Cr-1Mo steel, stress amplitude, σ_a, at fatigue limit hardy reduced by the application of mean stress, σ_m, since maximum stress, σ_max, exceeded the yield stress, σ_ys, by a small amount of tensile σ_m application and the shakedown behavior took place. While for the bolt specimen of SNB7, σ_a at fatigue limit reduced by tensile σ_m application, however, it tended to be constant when the σ_max exceeded the σ_ys to result in the shakedown behavior. It has been widely recognized that α is necessary to be considered for σ_a but not for σ_m in order to predict the effect of stress concentration on the fatigue limit. However, α should be considered for both σ_a and σ_m depending on the certain combinations of the material strength and the stress concentration condition.

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In the traffic machines such as the automobile, many thin wall closed section members made of steel are used for the improvement in the collision safety. In these members, the local buckling under compressive stress is mentioned as a main problem. In order to improve the mechanical performance of the member, the technique which fills the inside of closed section with the low-density foaming material is used. In this study, axial compression test and 3-point bending test at the various low deformation velocities from elastic region to plastic collapse were carried out on the composite material which filled the hat type thin-walled cross section member with 2 kinds of epoxy resin foaming material in which the foaming rate (density) is different. Characteristics of the energy absorption for composite member were estimated from the stress contribution ratio of the constructional member. This technique is effective as a simplified estimation method for characteristics of composite member in the design.

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Fiber Reinforced Plastics (FRP) has been applied in the aerospace field. In recent years, the application to the automobile field has been considering. In order to apply a FRP to the automobile field, not only the strength, but the fracture has to be determined, due to crash of a car. Authors have been working for the FRP to use of an energy absorbing device. In this paper, fracture mechanism analysis of the FRP tube at initial stage had been done with the consideration of continuous random fibers. Especially the initial micro-fracture of the trigger part of FRP tube was observed, and the transition process of initial micro-fracture to a continuous and stable fracture which is called ‘progressive crushing mode’ was analyzed.

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This paper presents experimental results for the deformation properties of injection-molded glass fiber/polyamide 66 composites. A weighed amount of glass fibers was mixed with polyamide 66 using a twin extruder and the amount of glass fibers was varied from 17 to 41 vol%. Tensile tests were performed on flat tensile specimens. Specimens (C specimens) were prepared by cutting injection-molded plates in three different directions: parallel to the flow direction, normal to the flow direction, and 45° to the flow direction. Injection-molded specimens (M specimens) were also used. The effects of the specimen orientation and fiber volume fraction on the tensile properties were investigated. In addition, dynamic viscoelastic tests were performed and the effect of fiber orientation on the temperature dependence of the storage and loss moduli of skin and core layers of the composites was investigated. To correlate with the tensile properties, the microstructure of the fracture surfaces of the composites was examined by a scanning electron microscope (SEM). The Young’s modulus increased as the fiber volume fraction was increased from 17 to 41 vol%, but the maximum tensile strength was achieved at a fiber volume fraction of 27 vol%. For the same fiber volume fraction, the Young’s modulus and tensile strength of the 0° specimen were higher than those of the 45°and 90° specimens.

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The strain dependence of the reaction rate of rubbery materials with ozone was discussed on the basis of the activation energy and the strain energy. The stretched molecular chains of rubbery materials can acquire the strain energy to be excited to the higher energy level than that of unstretched molecular chains, which results in the temporary reduction of the activation energy of the degradation reaction. Our theory predicts the spinodal-like transition will occur for the evaluation behavior of the ozone cracks at the higher strain energy. We observed such transition phenomena on the rubbery materials for laminated rubber bearings. The ozone resistance of the rubber material can be predicted by our theory and the experiment in different strain conditions.

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This paper describes a method of remaining life prediction of aged RC-T girder bridges based on the concrete core test results. The prediction of remaining life of the bridge also can be quantitatively estimated by applying the J-BMS BREX system with the field inspection data. Then it needs to verify through the concrete core tests which extracted from some parts on main girders, deck slabs and bridge piers, such as carbonation depth, chloride ion content, etc. In this paper, two aged bridges(about 70 years old) being demolished were selected for developing a method of remaining life prediction of the bridge in case where the main deterioration factor is carbonation and chloride attack. As a result, a flowchart of the remaining life prediction in the case of the chloride attack is more dominant than the carbonation and the case of the carbonation is more dominant than the chloride attack on deterioration process of the bridges was proposed based on the collected concrete core test results. Furthermore, it has been found that the remaining life for two aged bridges can be predicted accurately based on the proposed method with the accumulated values, 75mg/cm² of corrosion of reinforcing bar due to both of carbonation and chloride attack.

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