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 引用本文: 华奋飞, 罗彤, 雷剑, 刘大彪. 基于高阶应变梯度塑性理论的受限薄层剪切问题研究. 力学学报, 2024, 56(2): 399-408.
Hua Fenfei, Luo Tong, Lei Jian, Liu Dabiao. Study of confined layer plasticity based on higher-order strain gradient plasticity theory. Chinese Journal of Theoretical and Applied Mechanics, 2024, 56(2): 399-408.
 Citation: Hua Fenfei, Luo Tong, Lei Jian, Liu Dabiao. Study of confined layer plasticity based on higher-order strain gradient plasticity theory. Chinese Journal of Theoretical and Applied Mechanics, 2024, 56(2): 399-408.

## STUDY OF CONFINED LAYER PLASTICITY BASED ON HIGHER-ORDER STRAIN GRADIENT PLASTICITY THEORY

• 摘要: 针对受限金属薄层在剪切塑性变形时出现明显尺度效应这一问题, 现有理论分析多采用纯剪切假设和传统钝化边界条件, 其理论预测与实验结果不符. 文章采用黏弹塑性本构模型, 对Gudmundson高阶应变梯度塑性理论进行了有限元实现, 深入研究了金属薄层受限剪切的塑性变形机理. 考虑因界面倾斜引起的附加压应力, 采用自定义平面单元对材料的压缩−剪切组合变形进行了有限元模拟. 根据表面解锁的物理机制, 引入“软−硬”中间态的边界条件. 结果表明, 在压缩−剪切组合变形条件下, 受限薄层的剪切流动应力明显低于纯剪切条件下的流动应力, 而压应力的存在降低了剪切屈服强度. 利用周期性钝化边界条件, 能够定量描述界面处几何必需位错饱和引起的边界条件变化, 理论预测与实验结果吻合. 相关研究揭示了加载方式和高阶边界条件在受限薄层剪切尺度效应问题中的重要作用.

Abstract: In addressing the size effect observed in the plastic deformation of confined metallic thin layers, existing theoretical analyses have relied on pure shear assumptions and traditional passivation boundary conditions. However, their theoretical predictions are not in agreement with experimental results. In this paper, the finite element implementation of Gudmundson's theory of higher-order strain gradient plasticity is carried out based on the elasto-viscoplastic constitutive model. The method is then applied to study the plastic deformation mechanism in the shear of confined metallic layers. This study considers the additional compressive stress resulting from the inclined interface, and the combined compression-shear deformations are modeled through the user-defined plane element. In addition, a "soft-hard" boundary condition corresponding to the intermediate state is also introduced according to the physical context of surface unlocking. The results demonstrate that the shear flow stress of the confined layer under combined compressive and shear loads is significantly lower than that of the confined layer under pure shear, indicating that compressive stress dramatically reduces the yielding shear stress. The transition of the boundary condition due to the saturation of geometrically necessary dislocations at the interface is quantitatively characterized using the periodically passivated boundary condition. The theoretical predictions are in agreement with experimental data. The study emphasizes the importance of loading and boundary conditions in the size-dependent plasticity of confined layers.

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