基于3D-ILC单轴拉伸双平行内裂纹扩展规律研究

多裂纹相互作用是断裂力学研究的重要内容,但是针对单轴拉伸下的三维多内裂纹相互作用研究较少。基于3D-ILC技术,在完整立方体试件中生成三维双平行内裂纹,对不同错距d开展单轴拉伸试验,分析了断裂过程、应力云纹、起裂与破坏荷载及断口特征,基于M积分和MTS准则开展裂纹扩展路径及相互作用模拟。结果表明：①内裂纹错距为2 mm时相互“吸引”,错距为6与10 mm先相互“吸引”后“排斥”;②三维双内裂纹单轴拉伸下具有“合并分界”、“漏斗状”特征等断裂形态,其中裂纹中心侧发生I-II型复合断裂,外侧发生纯I型断裂;③初始应力云纹在预制裂纹尖端呈现“花瓣状”,裂纹相互“吸引”过程中应力云纹在中心侧裂纹尖端呈现“括弧状”;④试样强度与裂纹间错距成正比,错距为2,6,10 mm抗拉强度相对完整试样下降百分比分别为63.39%,50.79%,41.09%。起裂荷载与最终破坏荷载的比值分别为12.92%,15.16%,13.57%;⑤基于M积分,得出内裂纹I、II型应力强度因子分布规律,基于MTS裂纹扩展判据,实现三维双内纹的相互作用扩展全过程数值模拟,与试验一致。研究结果为三维双平行内裂纹相互作用研究提供试验与理论基础。

Propagation of double internal cracks under uniaxial tension based on 3D-ILC

The multiple-crack interaction is an important research topic in fracture mechanics, but few studies have focused on the interaction of 3D internal cracks under uniaxial tension. 3D double internal cracks are generated based on 3D-ILC. Uniaxial tensile tests are performed on the specimens with different vertical spacings (d). The fracture process, stress moire, crack initiation, failure load and fractography are analyzed. Then the numerical simulation is carried out. The results show that: (1) The the two cracks attract eath other when d is 2 mm, while they first attract then repulse each other when d is 6 or 10 mm. (2) The fracture morphologies such as “intersection boundary” and “funnel” are observed. I-II mixed-mode fracture occurs inside the crack, and mode I fracture occurs at the outer side. (3) Through the stress moire, the petal-shaped stripe can be observed at the crack tips, and the parentheses-shaped stripe appears during the process of attraction. (4) The strength of the specimens is proportional to d. Compared with that of the intact samples, the tensile strength decreases by 63.39%, 50.79% and 41.09%, respectively. (5) The distributions of mode I and II stress intensity factors are obtained based on M-integral, and the crack propagation is simulated according to MTS, which is consistent with the tests. The results may provide experimental support for the corresponding theoretical researches.