The present paper proposes a flexible Gurtin-type strain gradient crystal plasticity (SGCP) model based on generalized non-quadratic defect energy and uncoupled constitutive assumption for dissipative processes. A power-law defect energy, with adjustable order-controlling index n, is proposed to provide a comprehensive investigation into the energetic length scale effects under proportional and non-proportional loading conditions. Results of this investigation reveal quite different effects of the energetic length scale, depending on the value of n and the type of loading. For n ≥ 2, regardless of the loading type, the energetic length scale has only influence on the rate of the classical kinematic hardening, as reported in several SGCP works. However, in the range of n < 2, this parameter leads to unusual nonlinear kinematic hardening effects with inflection points in the macroscopic mechanical response, resulting in an apparent increase of the yield strength under monotonic loading. More complex effects, with additional inflection points, are obtained under non-proportional loading conditions, revealing new loading history memory-like effects of the energetic length scale. Concerning dissipation, to make the dissipative effects more easily controllable, dissipative processes due to plastic strains and their gradients are assumed to be uncoupled. Separate formulations, expressed using different effective plastic strain measures, are proposed to describe such processes. Results obtained using these formulations show the great flexibility of the proposed model in controlling some major dissipative effects, such as elastic gaps. A simple way to remove these gaps under certain non-proportional loading conditions is provided. Application of the proposed uncoupled formulations to simulate the mechanical response of a sheared strip has led to accurate prediction of the plastic strain distributions, which compare very favorably with those predicted using discrete dislocation mechanics.

Based on Monte Carlo method, the characteristic of exchange bias is discussed in diluted antiferromagnets in FM/AFM bilayers by changing the dilute concentration. The simulation results show that the exchange bias in FM/AFM bilayers can be enhanced significantly by introducing nonmagnetic atoms into the AFM layers. And there is a maximum in the diagram of exchange bias as a function of the dilute concentration, i.e., the exchange bias at first increases then decreases with increasing concentration of dilution at the same temperature. Besides, the maximum of the exchange bias occurs at lower concentration for higher temperature. These are consistent with the results of Phys. Rev. Lett. 96 117204 (2006). The cause of these results is that the spin distribution and the magnetic domain structure change greatly when varying dilute concentration. The exchange bias is maximal when the positive and the negative magnetic domains form a connected network. In addition, at the same concentration of dilution, by comparing the results of the random and regular dilution, we find that the exchange bias are more strongly increased by regular dilution than by random dilution for the FM/AFM bilayers, which shows further that the characteristic of exchange bias in FM/AFM bilayers depends on the interface spin-microstructure.