Recent earth environment problem is accelerating rapid popularization of hybrid or electric vehicles replacing conventional vehicles powered by fossil fuels. The electric vehicles don't need exhaust pipes and power train system like propeller shaft under the floor, so their floors 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 the usage is considered as 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 directions 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 the energy absorption for the crash in x direction was achieved and Pareto curves for the objectives were obtained.

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As regard to car frontal crash, previous research has indicated that front side member plays major role in energy absorption. For protecting the passengers, the front side member is expected to absorb crash energy as much as possible. In this study, we investigated the crash characteristics of half cut type side member structure by optimal design method to improve the performance for energy absorption. We developed an automatic optimal design system, in which the analysis meshes are generated with a group of design parameters and shape optimization is carried out automatically. The design variables are side member cross section shape, spot welding pitch length, divisional section number and radius difference along the axial direction, and the number of subdivision levels. As the result, the optimal side member structure with half cut type is capable of absorbing 1.44 times (1.29 times per unit mass) more energy than the original rectangular cross sectional side member structure with half cut type which is generally used.

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Laminated composite structures are widely used for aerospace components because of their high specific strength and specific stiffness. For laminated composite structures, stacking sequence optimization is indispensable. Although fracture of the laminated composites is usually used as a constraint, it is very important to obtain an accurate approximation of the fracture of the laminated composites for the optimization of surrogate models. Approximating the fracture of laminated composites, however, is quite difficult because the fracture index is very noisy. In the present study, a new surrogate model using the Kriging model for the fracture of laminated composites is proposed and tested for the most severe plate bending problems.

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Many applications use a combination of a local optimum search (LOS) and a genetic algorithm (GA), called a hybrid genetic algorithm (HGA), to solve problems. This hybrid can improve the performance of finding optimum solutions, but the HGA may produce redundancy when applying an LOS to inappropriate populations. This redundancy is the cause of high computation time, and it generates premature convergence and decreases HGA performance. This research therefore aims to reduce redundant LOS in HGAs. We propose a new technique called diversity selection (DS) and measure redundancy when applying an LOS in HGA. In this work, the DS selects appropriate populations to which to apply an LOS. The experiment then compares DS with other HGAs on numerical optimization problems. In addition, the HGAs were tested on two LOSs, a Nelder-Mead method and a quasi-Newton method to compare the speed of finding the optimum point in an LOS. The experimental results show that DS was able to quickly find the optimum point and give fewer redundant LOSs than other HGAs.

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By means of reaction pathway analysis, we have investigated the nucleation of 90° and 30° partial dislocation from a sharp corner in an f.c.c. crystal copper. The anisotropy aspects of dislocation nucleation revealed by the results have shown that the stress-dependent activation energy of 30° partial dislocation is approximately twice over the counterpart of 90° partial dislocation, and that the maximum inelastic displacement for the former is also higher. Moreover, the shape of the saddle-point configuration of 30° partial dislocation is similar to a half-ellipse whereas in the case of 90° partial dislocation it is more like a semi-circle, reflecting the different Peierls barriers influenced by the Burgers vectors. Further study of the surface reconstruction demonstrates that although the nucleation of 30° partial dislocation has been enhanced by surface reduction, it is still more energy-unfavorable than the 90° partial dislocation. These results suggest that the higher Peierls barrier is responsible for the larger activation energy of 30° partial dislocation nucleation.

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Hydrogen-enhanced localized plastiticity (HELP) is recognized as a viable mechanism of hydrogen embrittlement. A possible way by which the HELP mechanism can bring about macroscopic material failure is through hydrogeninduced cracking. In this work, according to the HELP theory, a constitutive formulation for elastoplasticity model in the presence of hydrogen is presented. To model the local phenomena associated with hydrogen, the local flow stress is considered decreasing with the increasing of hydrogen concentration. Following the previous work, a new module in the open source code ADVENTURE-Solid has been developed by the authors through considering the effect of hydrogen on material softening in microscale, which equips the open source code ADVENTURE-Solid software for studying hydrogen-plasticity interactions. We then combine the ADVENTURE-Solid with an in-house advection diffusion finite element program, to analyze a transient hydrogen diffusion-elastoplastic coupling problem ahead of a crack tip. To validate the new module in the ADVENTURESolid, a set of numerical test cases are presented and discussed. Obtained results show good agreement with previous results.

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