平面应力裂端约束与J控制裂纹稳态扩展

 利用有限元法计算模拟了紧凑拉伸和中心裂纹两种试样在Ⅰ型平面应力条件下的裂纹准静态扩展过程。结果表明:两种不同的薄板试样中扩展裂纹尖端约束和应力场完全满足静态裂纹HRR奇异性解的相应要求,即对于扩展裂纹J主导裂端场条件依然有效。值得注意的是:与平面应变情形相反,在平面应力条件下,较高的J主导水平发生在纯拉伸条件下,而较低的J主导水平发生在纯弯曲条件。由两种试样实测及有限元计算模拟的平面应力J阻力曲线符合良好。因而,作为一个独立于试样几何的准则,平面应力J阻力曲线适于表征材料抵抗裂纹稳态扩展阻力,并且能够合理地用于评估给定材料状态条件下的薄壁含裂纹构件和结构的安全性。

CRACK-TIP CONSTRAINT AND J-CONTROLLING STABLE GROWTH OF CRACK IN PLANE STRESS CASE

The finite element analyses are performed to model quasi-static crack growth under mode I plane stress in a compact tension specimen and a centre-cracked plate. It is found that the crack-tip constraint and stress field defined by HRR singularity solution for a stationary crack are better met by those presented in the propagating crack tip for two different thin specimens, namely, J-dominance is continuously valid for the tip field of a growing crack. Contrary to plane strain, it is noted that, for plane stress case, the higher J-dominance level occurs under pure tension condition, and the lower J-dominance level occurs under pure bending condition. The J-resistance curves measured experimentally from the two specimens geometries coincide with each other and agree well with those calculated by FEM simulations. Therefore, J-R curves under plane stress mode I codition, as a criterion independent of specimen-geometry, are suitable to characterize the materials resistance against crack steady extension and can be reasonably used to appreciate the safety of the thin-walled cracked components or structures for the given material state.