个人信息Personal Information
学历：博士研究生毕业
学位：工学博士学位
性别：男
学科：力学. 航空宇航科学与技术. 材料科学与工程. 机械工程. 冶金工程. 先进制造. 航空工程. 材料工程. 冶金工程. 机械工程. 固体力学
多尺度与微纳米力学，梯度结构材料，界面力学，固体本构关系，应变梯度理论，晶体塑性有限元，离散位错动力学，分子动力学，高熵合金，大数据与机器学习，材料基因，极端力学，高性能材料
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2021-12-21 博士生陆宋江论文“Size-dependent yield stress in ultrafine-grained polycrystals: A multiscale discrete dislocation dynamics study”在期刊 International Journal of Plasticity在线发表
Highlights
•A polycrystal model containing > 100 grains with dislocation-penetrable grain boundaries was constructed within a discrete dislocation dynamics framework.
•The effects of dislocation source parameters and grain size on the yield stress of ultrafine-grained polycrystals were systematically studied.
•In the initial, grain boundary dominated regime, the change of dislocation density is proportional to plastic strain and independent of the initial dislocation density.
•The combined effects of source length, grain size, and initial dislocation density on flow stress can be captured by a single equation.
Abstract
In this study, the effects of grain size and dislocation source properties on the yield stress of ultrafine-grained (UFG) polycrystals were examined using three-dimensional multiscale discrete dislocation dynamics (DDD). A polycrystal model containing multiple grains with randomly distributed orientations was constructed within a multiscale DDD framework. Grain boundaries (GBs) were assumed to be penetrable by dislocations, with two dislocation-GB interaction mechanisms, i.e., dislocation absorption at GBs and dislocation emission from GBs, being considered. The simulation investigated the dislocation source effect and demonstrated a non-monotonic dependency of flow stress on dislocation source length, where the lowest flow stress corresponds to a Frank-Read (FR) source length of d/4 where d is the grain size. When the length of a FR source in the polycrystalline sample exceeds this value, the simulated yield stress increases owing to the constraining effect of grain boundaries on dislocation movement. The grain size dependence of the yield stress shows deviations from the classical Hall–Petch relationship as the exponent in the Hall–Petch type relation ranges from about 0.91 to about 0.98, depending on the initial dislocation density in the samples. Detailed analysis indicates that the grain size dependence of the yield stress is mainly controlled by the effect of grain boundary constraints on dislocation activation. A secondary effect arises from grain size dependent dislocation accumulation and the resulting Taylor hardening. The activation and operation of FR sources were quantitatively examined to further understand the origins of source length and grain size effects. A theoretical model is proposed to account simultaneously for the effects of source length, grain size, and initial dislocation density on the yield stress of polycrystals in the UFG regime.
Link
https://doi.org/10.1016/j.ijplas.2021.103183