多裂纹介质在动态载荷作用下的断裂特性研究

采用含双平行裂纹的半圆盘有机玻璃模型,以落锤作为动态加载装置,对动态载荷下多裂纹介质的断裂行为进行了研究。研究结果表明:在动载作用下,含多裂纹的脆性材料的应力场与单一裂纹时的应力场有明显不同。多裂纹介质中裂纹尖端的应力场多为拉剪混合应力场,裂纹起裂多为I-II混合型裂纹,但当裂纹扩展以后,裂纹逐渐向拉伸破坏转变;在多裂纹介质中,当已有一条裂纹扩展时,邻近平行裂纹尖端的能量被释放,邻近平行裂纹尖端的应力集中程度也逐渐下降,说明扩展裂纹对相邻平行裂纹的起裂和扩展有一定的抑制作用;在动载作用下,多裂纹介质中裂纹的起裂韧度KI由2.86 MN/m2下降到1.95 MN/m2,说明多裂纹对介质的起裂韧度有影响。但当试件中有一条裂纹扩展后,邻近平行裂纹对扩展裂纹的传播韧度和扩展速度的影响逐渐减弱。

Study on Fracture Property in multi-crack medium under Dynamic Loading

A series of experiments were conducted on polymethyl methacrylate (PMMA) using semi-circular bending specimen containing multi-cracks to study dynamic fracture behaviors of multi-cracks medium under impact loading. The results show that: under dynamic loading, the stress field of brittle material containing multi-cracks was different from the stress field of brittle material containing single crack. The stress field around crack tips in multi-cracks medium was always tension-shear stress field, the crack initiation was mode I-II, but when the cracks propagated, the cracks appeared tension failure; in multi-cracks medium, when a crack propagated, the energy of the neighbor crack would release, stress concentration decreased, which means cracks propagation prevented the initiation and propagation of the neighbor crack; under dynamic loading, the initiation fracture toughness in multi-cracks medium decreased from 2.86 MN/m2 to 1.95 MN/m2,which showed that multi-cracks affected initiation fracture toughness, however, when a crack propagated, the neighbor crack could not affect the initiation fracture toughness and crack velocity.