热载荷下脆性固体中三维平行内裂纹的相互作用:实验和数值模拟

Interaction of 3D parallel internal cracks in brittle solids under thermal loading: Experiment and numerical simulation

热断裂是一种典型断裂。裂纹广泛存在于脆性固体中,温度变化下裂纹的应力集中与扩展对于热断裂有着重要影响。传统研究大多集中在表面裂纹或二维裂纹,而对于温度场下内裂纹的扩展及多内裂纹的相互作用研究较少。本文使用3D-激光疲劳内裂纹(3D-ILC)方法,在完整立方体试件内制作三维双平行内裂纹,对表面不造成任何损伤。开展了温度场下不同垂直间距内裂纹断裂物理试验和三维数值模拟,并对双裂纹相互作用模式进行了分析讨论。结果表明:1)当双裂纹共面时,内裂纹两侧温度场分布对称,双裂纹扩展方向不发生偏移,内裂纹内侧尖端相互吸引最终融合,属于Mode-I型裂纹。此外共面裂纹扩展迹线相交呈“I”形断口特征。2)双裂纹垂直间距d与裂纹半径a之比d/a<2时,双裂纹相互吸引并融合,且当d/a=1时相互作用程度最大,非共面裂纹迹线交并为“月牙形”断口特征。3) d/a≥2后双裂纹内侧尖端扩展呈“排斥”,而“排斥”现象是边界效应导致,并非多裂纹间相互作用,属于Ⅰ-Ⅱ型复合裂纹。4)不论垂直间距大小,内裂纹两侧尖端均存在应力集中现象,且内侧远大于外侧,故内侧裂纹扩展长度大于外侧。研究结果为温度场下三维双平行裂纹相互作用的研究提供了实验和理论依据。

Thermal fracture is a typical fracture. Cracks are widely present in brittle solids, and the stress concentration and propagation of cracks under temperature changes have an important effect on thermal fracture. Most of the traditional studies have focused on surface cracks or 2D cracks, while the propagation and the interaction of multiple internal cracks under temperature field are less frequently covered. This paper uses the 3D-internal laser-engraved crack(3D-ILC) method to fabricate 3D double-parallel internal cracks within intact cubic specimens, without causing any damage to the surface. Physical experiments and 3D numerical simulations of crack fracture in different vertical spacing under temperature fields are carried out, and the double crack interaction mode is analyzed and discussed. The results indicate the following: 1) When the double cracks are coplanar, then the temperature field distribution on both sides of the internal crack is symmetrical, the direction of double crack propagation does not shift, and the inner tips of the internal cracks attract each other and eventually coalesce. This is categorized as Mode I crack. In addition, coplanar crack propagation arcs intersect in an “I” shaped fracture morphology. 2) Double cracks attract and coalesce with each other when the ratio of vertical spacing d to crack radius a, i.e., d/a<2, and the interaction degree is maximum when d/a=1.Non-coplanar crack arcs are intersected by “crescent” shaped fracture morphology. 3) After d/a≥2, the propagation of the inner tip of the double crack is repulsive and this repulsion phenomenon is caused by the boundary effect, not the interaction between multiple cracks, thus categorizing them as Mode Ⅰ-Ⅱ mixed cracks. 4) Regardless of the size of the vertical spacing, the stress concentration phenomenon is present on both sides of the tip of the internal crack, while the inner side is much larger than the outer side, so the inner crack propagation length is longer than the outer side. The results of this study provide an experimental and theoretical basis for the study of three-dimensional double-parallel crack interactions under temperature fields.