材料期刊网

本文基于超高强度钢复合型脆断的实验结果,利用线弹性近似分析和弹塑性有限元分析,对不同的K_(Ⅱ)/K_Ⅰ值脆断的试样,在临界状态时裂纹顶端的塑性区进行了研究,得到了裂纹起始扩展时塑性区的形状和尺寸、裂纹顶端周围应力、应变以及应变能密度的分布情况。根据这些结果,对复合型裂纹扩展阻力的影响因素提出了看法,对现有的复合型断裂准则做了讨论。

The crack-tip plastic zone in mixed-mode brittle fractured specimens of different K_Ⅱ/K_Ⅰ ratio of a high strength steel has been investigated under critical conditions. Both elastic approximate analysis and elastic-plastic finite element method were used to analyze the distribution of stress, strain and strain energy density in the vicinity of the crack-tip. It is shown that:(1) at the initial moment of crack growth, the (σ_θ)_(cr) and S_(cr) are notmaterial parameters, but increase with K_Ⅱ/K_Ⅰ;(2) for all specimens fractured under linear elastic condition, the crack tip plastic zone area of mode Ⅱ is larger than that of mode Ⅰ by two order of magnitude and the total plastic work absorbed before brittle fracture markedly increases with K_Ⅱ/K_Ⅰ;(3) the higher the K_Ⅱ/K_Ⅰ ratio is, the lower the σ_m/(?) in the vicinity of crack tip and initial growth directions;(4) under mode Ⅰ condition, the area of the plane stress plastic zone at specimen surface is larger than that of the plane strain plastic zone at the centre of the same specimen by a factor of 3. However, with the increase of K_Ⅱ component, their difference decreases. Therefore, the influence of thickness on mixed-mode brittle fracture toughness might be smaller than on mode Ⅰ.Besides, the increase of hydrostatic tension stress under plane stress condition is quite different from that under plane strain condition. Once the crack tip zone falls into plastic state, the increase rate of the hydrostatic tension stress in the plane stress crack tip zone will become gentle instantaneously, but scarcely any such change would be observed under plane strain condition. It seems that at the initial growth moment the hydrostatic tension stress in the plane stress plastic zone is much smaller than in the plane strain plastic zone.