It has been reported that stress corrosion cracking damaged in-core monitor housing, which occurred in weld heat-affected zone because of the existence of residual stress. So it is important to evaluate crack growth behavior with high accuracy. In this study, crack growth behavior in ICM Housing is estimated using S-version FEM (S-FEM), which allows generation of core finite model and the detailed mesh representing the crack independently. At First, axial, slant and circumferential surface crack are assumed at two locations where residual stress fields are different from each other. One is isotropic residual stress field, and another is circumferential residual stress field. It is shown that crack growth behaviors are different under different residual stress fields. Next, effect of the slit, which exists between ICM Housing and Pressure Vessel is evaluated. It is shown that the existences of slit increases stress intensity factors of growing surface crack. Finally S-FEM results are compared with those of Influence Function Method (IFM), which assumes that an elliptical crack shape exists in a plate. It is shown that IFM result is conservative than that of S-FEM.

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To evaluate an effect of a residual stress improvement using freezing process (FP) for a butt-welded small bore pipe, an application test and a finite element analysis (FEA) were conducted. An accelerated stress corrosion cracking (SCC) test was conducted using a boiling 42% magnesium chloride (MgCl₂) solution for as-weld and after FP specimens made of low-carbon austenitic stainless steel (Type 316L). Test results show that SCC occurrence distributed in circumferential direction, and decreased by FP. In addition, weld residual stress of small bore pipes was evaluated using three-dimensional thermal elasto-plastic FEA with mixed hardening law. Since residual stress of a small bore pipe is sensitive to welding process, especially for a welding end position, the three-dimensional FEA is required to consider an effect of a moving heat source during a butt-weld process. FEA results show that effect of a nominal diameter on a residual stress improvement is significant for a small bore pipe. Applicability of FEA method for FP was confirmed by comparison with test results. Moreover, a revised criterion for FP was proposed on the basis of FEA results.

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The effects of cyclic internal pressure and thermal changes on the sealing performance and mechanical behaviors in pipe flange connection are examined using the FEM analyses for pipe flange connections with spiral wound gasket (SWG). The contact gasket stress distributions and the axial bolt forces taking into account the cyclic internal pressure and thermal changes are demonstrated. The load (internal pressure, thermal changes) sequences are determined from the conditions for actual pipe flange connections used in petroleum and chemical plants. Furthermore, the effect of material differences between pipe flange and bolts on the contact gasket stress distribution are examined. From the FEM results, it is found that the contact gasket stress reduces to be the smallest when a plant is restarted. The reduced contact gasket stress should be taken into account in the sealing design of the connection. On the other hand, the leakage tests were carried out to verify the FEM results and the effect of number of cycles (for 21days). A fairy good agreement is seen between the estimated amount of leakage due to the contact gasket stress distributions obtained from the FEM and the measured amount of leakage. It is found that the contact gasket stress decreases when the plant is restarted and as the temperature decreases. At that time, the contact gasket stress is the smallest which may lead to a leakage accident.

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The CED (Crack Energy Density) was proposed first with ordinary materials in mind as the parameter that is defined regardless of constitutive equation and enables a unified description of behavior of a crack throughout its life. Subsequently the concept was extended, on the basis of facts that its applicability had been shown successfully for ordinary materials, so as to be applied to piezoelectric materials and some fundamental relations related to CED and its derivatives such as mechanical and electrical parts of CED and electrical enthalpy density were given. Aiming at exploring the applicability of these quantities to crack problems for piezoelectric materials, in this paper, a method for evaluating CED and its derivatives numerically with practically sufficient accuracy through finite element analyses of a piezoelectric material is studied concretely by using the relations above. As a result, it is shown that the values of mechanical and electrical parts of CED depend on the loading history, that is, how to apply mechanical and electrical loads, even for a linear problem and its influence should be taken into consideration, while CED and electrical enthalpy density are independent of the loading process.

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This paper proposes a topology optimization procedure for magnetostrictive actuator problems. It is useful for the efficient geometrical design of actuator shapes because their shapes have been empirically designed and are not necessarily optimum. In the proposed topology optimization procedure, a level set field over a fixed design domain is introduced to implicitly represent their shapes and its second order gradient term analogous to phase field is also introduced to control its geometrical complexity. Adjoint variable method is utilized for its sensitivity analysis. To verify the proposed topology optimization procedure, numerical experiments of push rod part and magnetostrictive rod parts to maximize mechanical displacement under magnetic fields are demonstrated.

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Rupture of atherosclerotic plaque in coronary artery causes serious results. Since heterogeneously distributed plaque may cause local stress concentration, the local strain in circumferential direction of the coronary artery with atherosclerosis was investigated. For eight specimens from four human atherosclerotic coronary arteries, four needles were stuck into each the specimen at equal intervals on their circumference. Specimens were pressurized and local circumferential length was calculated from movement of the needles observed from longitudinal direction. For each specimen, pressure strain elastic modulus E_p, stiffness parameter β, and incremental elastic modulus E_inc were calculated. Local circumferential strain was calculated by referring to circumferential length at no-stress state. Total thickness T_total, plaque thickness T_plaque, medial and adventitial wall thickness T_wall, and area fraction of plaque A_plaque were also measured in histological sections. E_p and β obtained in the present study were almost comparable to those of nonatherosclerotic human coronary arteries in previous studies. Local strains were different even in a circumference. The local strain at 80 mmHg ε₈₀ correlated significantly with T_wall (r = 0.48, p < 0.05), while ε₈₀ had insignificant correlation with T_plaque, T_total, and A_plaque. Coefficient of variance of local T_wall decreased with the increase in the pressure. These results indicate that mechanical properties of human atherosclerotic coronary arteries are heterogeneously distributed in circumferential direction, plaque has insignificant effect to their mechanical properties, and T_wall becomes more uniform at physiological state than at no-stress state. These dada may be useful to simulate stress distribution in atherosclerotic coronary artery.

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The cyclic creep of patellar tendons was in vivo evaluated in five male subjects. The cyclic stress (0-10 MPa) was applied to the patellar tendons by isometric knee extension contractions. The force in the patellar tendons was determined from the knee moment and the deformation of the patellar tendons was measured using ultrasonography. Stress was calculated by dividing the patellar tendon force by the patellar tendon cross-sectional area measured using ultrasonography. Strain was determined from dividing the patellar tendon deformation by the initial patellar tendon length. From these data, the stress-strain relations were obtained. The strain at the stress of 10 MPa increased from 5.9 % to 7.6 % with the cyclic loading until 10 cycles and thereafter was almost constant. The tangent modulus decreased from 322 MPa to 242 MPa with the cyclic loading until 10 cycles and thereafter was almost constant.

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This paper presents a design method to visualize the loading history under non-proportional multiaxial loading with the principal direction change. Definitions of principal stress and strain ranges and mean stress and strain were firstly introduced by utilizing Itoh-Sakane criterion for general multiaxial loading including non-proportional loading. Secondly, the method of calculating the non-proportional factor which expresses the severity of non-proportional loading was discussed for the general multiaxial 3D loading. The paper proposed a method of visually presenting the principal stress and strain trajectory under non-proportional loading histories that assists designers to understand the loading mode whether proportional or non-proportional under 3D multiaxial loading. An actual method of taking account of the stress and strain multiaxiality into practical design of components and structures was described.

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Honeycomb sandwich panels are used as lightweight panels when a high bending stiffness is required, such as aircraft, train and architectural materials. Aluminum honeycomb cores have been used as the core materials of sandwich panels, however, there is a problem that the manufacturing cost of sandwich panels using aluminum honeycomb cores is very high. By the way, we have developed the SMART SHEET^® which has a large second moment of area in arbitrary cross sectional dimensions in order to increase the bending stiffness in all directions. The SMART CORE^® panel, which uses the SMART SHEET as the core material instead of the honeycomb core, can be used as an alternative sandwich panel. In this study, the bending stiffness of the SMART SHEET, the SMART CORE and the honeycomb panel have been investigated using the three point bending test. The results showed that the bending stiffness of the SMART SHEET and the SMART CORE are higher than that of the honeycomb panel.

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