高强度结构钢的韧性启裂和稳态扩展

研究了具有一定韧度的高强度结构钢裂纹早期扩展阻力与材料的微观组织结构、应力状态、变形历史和应变特性之间的关系。结果表明:裂纹扩展阻力(指J_R阻力曲线中的J_i和dJ/da)主要决定于裂纹尖端的塑性约束程度和应力应变场中消耗的弹性能和塑性功。这与三轴应力状态函数σ_mσ~(1/2)有关。材料的流变曲线描述了形变过程中的变形历史和应变特性,有明显的阶段性,其中第Ⅱ阶段的变形历史和应变特性制约着裂纹的启裂过程,第Ⅲ阶段的变形历史和应变特性制约着裂纹的扩展过程。应变硬化率dσ/dε可以敏感地反映出材料内部的应力分布和微观断裂机制。

DUCTILE CRACK INITIATION AND STEADY-STATE PROPAGATION OF HIGH STRENGTH STRUCTURAL STEEL

The resistance to crack propagation at earlier stage for a high strengthstructural steel of certain ductility with relation to its microstructures, stressstates, deformation history and strain characteristic has been investigated. The resist-ance to crack propagation is mainly determined by the plastic constrain ahead ofthe crack tip and the elastic energy and plastic work absorbed in the stress-strainfield. These are connected with the state function of triaxial stress. The deforma-tion history and strain characteristic during deformation of material are describedby the flow line in which the deformation history and strain characteristic re-strain the crack initiation at stage II and the crack propagation at stage III. Thestrain hardening rate may sensitively reflect the stress distribution and micro-frac-ture mechanism in the interior of material.