K. Hashiguchi¹ and T. Ozaki²

The International Conference on Computational & Experimental Engineering and Sciences, Vol.4, No.4, pp. 243-250, 2007, DOI:10.3970/icces.2007.004.243

Abstract The overstress model is improved by incorporating the novel variable "overstress tensor" reaching the current stress from the subloading stress evolving in an imaginary quasi-static process of elastoplastic deformation due to the extended subloading surface model with the tangential inelastic strain rate. More >

E.T.R. Dean¹

The International Conference on Computational & Experimental Engineering and Sciences, Vol.4, No.4, pp. 231-242, 2007, DOI:10.3970/icces.2007.004.231

Abstract The shapes of yield envelopes for soils and other materials are generally taken as the starting point of a macroscopic plasticity model. This paper shows that these shapes can be accurately predicted using recent advances in thermodynamics and the new concept of multi-scale patterns. Some implications for future models are discussed. More >

R. Matsumoto¹, N. Miyazaki¹, M. Nakagaki²

The International Conference on Computational & Experimental Engineering and Sciences, Vol.4, No.4, pp. 223-230, 2007, DOI:10.3970/icces.2007.004.223

Abstract The mechanical properties of amorphous metals and metallic glasses are remarkably changed by precipitated crystalline particles. In this paper, the effects of crystal particle size and volume fraction on the flow stress of the metallic glass are evaluated by molecular dynamics simulations. The investigated volume fraction ranges from 0% (metallic glass) to 100% (nanocrystalline metal), and the average particle diameter ranges from 1nm to 12nm. It is revealed that the dispersed particle effects on the flow stress are very small in the entire volume fraction range when the average particle diameter is smaller than 3 nm, and the flow stress… More >

S. Takashima¹, N. Miyazaki², T. Ikeda³, M. Nakagaki⁴

The International Conference on Computational & Experimental Engineering and Sciences, Vol.4, No.4, pp. 215-222, 2007, DOI:10.3970/icces.2007.004.215

Abstract Composite materials have complicated microstructures. These structures affect macroscopic deformation. In this study, we focus on the particle size effect in composite materials. For this purpose, we derived an elastic-plastic constitutive equation considering size effect by using Eshelby's theory and the strain gradient theory of plasticity. We performed a homogenized finite element analysis using the elastic-plastic constitutive equation. The results obtained from the analysis show increase of the strength with decrease of the particle size in composite materials. More >

N. Ohno¹, D. Okumura¹

The International Conference on Computational & Experimental Engineering and Sciences, Vol.4, No.4, pp. 207-214, 2007, DOI:10.3970/icces.2007.004.207

Abstract The self energy of geometrically necessary dislocations (GNDs) is considered to inevitably introduce the higher-order stress work-conjugate to slip gradient in single crystals. It is pointed out that this higher-order stress stepwise changes in response to in-plane slip gradient and thus directly influences the onset of initial yielding in polycrystals. The self energy of GNDs is then incorporated into the strain gradient theory of Gurtin (2002). The resulting theory is applied to model crystal grains of size D, leading to a D-1-dependent term with a coefficient determined by grain shape and orientation. It is thus shown that the self energy… More >

T. Asada¹, N. Ohno¹

The International Conference on Computational & Experimental Engineering and Sciences, Vol.4, No.4, pp. 201-206, 2007, DOI:10.3970/icces.2007.004.201

Abstract In this study, to determine incremental, perturbed displacement fields in periodic inelastic solids, an incremental homogenization problem is fully implicitly formulated, and an algorithm is developed to solve the homogenization problem. It is shown that the homogenization problem can be iteratively solved with quadratic convergences by successively updating strain increments in unit cells, and that the present formulation allows versatility in the initial setting of strain increments in contrast to previous studies. The homogenization algorithm developed is then examined by analyzing a holed plate, with an elastoplastic micro-structure, subjected to tensile loading. It is thus demonstrated that the convergence in… More >

H.S. Lee¹, W.S. Chu¹, Y.C. Kang¹, H.J. Kang¹, S.H. Ahn²

The International Conference on Computational & Experimental Engineering and Sciences, Vol.4, No.3, pp. 195-200, 2007, DOI:10.3970/icces.2007.004.195

Abstract The fuel cell is one of promising environment-friendly energy sources for the next generation. The bipolar plate is a major component of the Proton Exchange Membrane (PEM) fuel cell stack, and it takes a large portion of stack volume, weight and cost. In this study, as alternative materials for bipolar plate of PEM fuel cells, graphite composites were fabricated by compression molding and by machining. Graphite particles mixed with epoxy resin were used as the main substance to provide electric conductivity. Flow channels were fabricated by compression molding applying design of experiments (DOE) in order to evaluate moldability. The cost… More >

Song-Jeng Huang¹, Yan-Fu Liu²

The International Conference on Computational & Experimental Engineering and Sciences, Vol.4, No.3, pp. 187-194, 2007, DOI:10.3970/icces.2007.004.187

Abstract A digital shearographic (DS) technique is a tool well-suited for precision strain measurement and is a nondestructive testing technology. But the fringe patterns of shearography are not so clear. A phase-shifting technique is incorporated into DS and demonstrated to yield fringe patterns with good quality. The major purpose of this study is to produce a measuring system of digital phase-shifting shearography (DPSS) to measure out-of-plan strain of sandwich plate with fully-potted insert. The system mainly includes piezoelectric transducer, servo controller, Michelson shearing mechanism, image processing system and loading system. The Macy algorithm is used for program simulation, and applying noise… More >

S. Nishida¹, N. Hattori¹

The International Conference on Computational & Experimental Engineering and Sciences, Vol.4, No.3, pp. 179-186, 2007, DOI:10.3970/icces.2007.004.179

Abstract The authors have experimentally confirmed that the non-propagating microcracks are observed in the low carbon plain specimens subjected to the stress of fatigue limit by 1×107 cycles and not observed in those of pure copper and aluminum alloys etc.. In addition, there exists clear fatigue limit in typical austenitic stainless steel SUS304 but not exist the non-propagating micro-cracks subjected to the stress of fatigue limit by 1×107 cycles. On the other hand, there exist not only clear fatigue limit but also non-propagating micro-cracks in the high manganese austenitic steel (HMA 0.20%C steel). Then, the authors have focused to the existence… More >

Iwona Pokorska¹, Andrzej Sluzalec²

The International Conference on Computational & Experimental Engineering and Sciences, Vol.4, No.3, pp. 171-178, 2007, DOI:10.3970/icces.2007.004.171

Abstract This work has been focused on a unified approach for parameter identification in metal forming processes of poroplastic materials. In order to solve the associated inverse problem a chosen functional is minimized by the use of gradient based methods and a sensitivity analysis. Several numerical and experimental results were presented. These are: the direct problem of simple compression, re-identification of flow stress and identification of loading functions. More >