Influences of chemical compositions, heat treatment and microstructure on impact toughness of 15Cr ferritic steel have been investigated. Charpy impact values of the furnace cooled steels were lower than 15J/cm2 at room temperature independent of chemical compositions. Drastic improvement in impact toughness has been attained by controlling the carbon and nitrogen contents, by the addition of nickel and by the increase in cooling rate after annealing. However, the effect of nickel on impact toughness strongly depends on carbon and nitrogen contents. Improvement in impact toughness of the 15Cr ferritic steel has not been explained by individual microstructural factors of grain size, distribution of precipitates, volume fraction of martensitic phase. It has been supposed that the increase in Charpy impact toughness of the 15Cr ferritic steel was attained by improvement in toughness of ferrite matrix itself.
This paper suggests a material mixing method to mix several materials in a structure. This method is based on ESO (Evolutionary Structural Optimization), which has been used to optimize topology of only one material structure. In this study, two criterions for material transformation and element removal are implemented for mixing several materials in a structure. Optimal topology for a multiple material structure can be obtained through repetitive application of the two criterions at each iteration. Two practical design examples of a short cantilever are presented to illustrate validity of the suggested material mixing method. It is found that the suggested method works very well and a multiple material structure has more stiffness than one material structure has under the same mass.
In weaving welding where a V groove exists, the heat input distribution is an important factor that determines the defectiveness of the bead shape, undercut and over-lap. In this study, the amount of heat input, which is determined by the welding current, voltage, speed and weaving conditions is calculated through mathematical development and numerical methods. Furthermore, the heat input distribution as a two-dimensional heat source was observed when applied to each groove. Therefore, a heat input control algorithm is suggested to prevent the defects generated from undercut or over-lap, which was verified through an analysis of the heat input distribution.
In this paper, a closed form solution of a crack in magneto-electro-elastic composites under anti-plane shear stress loading is obtained for the permeable crack surface conditions. By using the Fourier transform technique, the problem can be solved with a pair of dual integral equations in which the unknown variable is the jump of the displacements across the crack surfaces. In solving the dual integral equations, the jump of the displacements across the crack surface is expanded in a series of Jacobi polynomials. The closed form solutions of the stress intensity factor, the electric displacement intensity factor and the magnetic flux intensity factor are given. It can be obtained that the stress field is independent of the electric field and the magnetic flux.
This paper presents the experimental and theoretical results of the response and collapse of 316L stainless steel tubes subjected to cyclic bending. The tube bending machine and curvature-ovalization measurement apparatus were used for conducting the curvature-controlled experiment. It was found that the response and collapse are similar to that of metal tubes found in literatures. Next, the endochronic theory and the principle of virtual work were used to simulate the response of 316L stainless steel tubes under cyclic bending. In addition, a proposed theoretical formulationwas used to simulate the relationship between the controlled curvature and the number of cycles to produce buckling. It has been shown that the theoretical simulations of the response and collapse correlate well with the experimental data.
The mechanism of the occurrence of longitudinal surface cracks near slab corner has been investigated based on both the thermal stress analysis of solidifying shell in the continuous casting mold and experimental consideration. In the stress model, the coupling between thermal deformation of the shell and temperature distribution in the mold wall was taken into account. It is cleared that the conventional constant-tapered mold is insufficient to prevent the cracks. By applying a newly developed variable multi-tapered mold, which was designed from the stress analysis, the high-speed castings of 5m/min have been put into practice without corner cracks.