Yoshiteru Aoyagi

Heterogeneous plastic deformation and Bauschinger effect in ultrafine-grained metals: atomistic simulations

The effect of the dislocation density on yield strength and subsequent plastic deformation of ultrafine-grained metals was investigated in large-scale atomistic simulations. Polycrystalline models were constructed and uniaxial tension and compression were applied to elucidate the heterogeneous plastic deformation and the Bauschinger effect. The initial yield becomes heterogeneous as the dislocation density decreases owing to a wide range of Schmid factors of activated slip systems in each grain. A different mechanism of the Bauschinger effect was proposed, where the Bauschinger effect of ultrafine-grained metals is caused by the change in dislocation density in the process of forward and backward loadings.

Multiscale Crystal Plasticity Modeling Considering Nucleation of Dislocations Based on Thermal Activation Process on Ultrafine-grained Aluminum

In this study, a crystal plasticity model expressing the behavior of the dislocation source and the mobile dislocations is proposed by considering a thermal activation process of dislocations. In order to predict the variation of critical resolved shear stress due to grain boundaries, mobile dislocations, or dislocation sources, information on these crystal defects is introduced into a hardening law of crystal plasticity. The crystal orientation and shape of ultrafine-grained (UFG) aluminum produced by accumulative roll bonding processes are measured by electron backscatter diffraction (EBSD). Mechanical properties of the UFG aluminum are estimated using tensile test and indentation test. Results obtained by EBSD are introduced into a computational model. Finite element simulation for polycrystal of aluminum investigates the effect of microstructure on mechanical properties of UFG aluminum.

Macroscopic Yield Function Predicted by Crystal Plasticity Simulation on Ultrafine-Grained Aluminum

In this study, using experiment results obtained by electron backscatter diffraction, information on crystal orientation is introduced into a computational model for crystal plasticity simulation considering the effects of grain boundaries and dislocation sources to express the effect of the microstructure of ultrafine-grained metals. Finite-element simulations are performed for a polycrystal of an aluminum plate under biaxial tension. The multiscale crystal plasticity simulations depict the yield surface of the ultrafine-grained aluminum produced by accumulative roll-bonding processes. The anisotropic material coefficients of a higher-ordered yield function for ultrafine-grained aluminum are derived using a genetic algorithm.