含圆孔缺陷三点弯曲梁的裂纹扩展特性实验研究

Tests for crack propagation characteristics of three-point bendingbeam with circular hole defect

采用动态焦散线实验系统,对含圆孔缺陷的PMMA材料进行冲击断裂力学实验,研究三点弯曲梁中不同直径和位置的圆孔缺陷对扩展裂纹的影响。实验结果表明:扩展裂纹与圆孔缺陷相互作用前,呈现Ⅰ型拉伸断裂,扩展路径平直;与圆孔缺陷相互作用后,贯通萌生的次裂纹沿直线继续扩展,未贯通的裂纹偏移扩展。扩展裂纹与路径上圆孔缺陷贯通过程中,裂纹扩展速度和动态应力强度因子快速降为零,裂纹的扩展受到抑制,且圆孔直径越大、距离越近,抑制作用越显著;贯通萌生次生裂纹的起裂速度和起裂韧度,随着圆孔缺陷直径的增大而变大。扩展裂纹与偏置圆孔缺陷相互作用过程中,当圆孔缺陷直径越大、偏置距离越小,裂纹起偏距离越短,最大偏移量越大,并且扩展裂纹动态应力强度因子和扩展速度局部小幅增大。研究结果为分析动态裂纹扩展特征和材料破坏模式提供借鉴。

Effects of circular hole defect with different diameters and positions on crack propagation characteristics was tested and studied for a 3-point bending beam with this hole defect made of PMMA material subjected to impact load using a dynamic caustic line test system.The results showed that before propagating crack interacts with circular hole defect,crack propagation reveals I type tensile fracture,and propagation path is straight;after propagating crack interacts with circular hole defect,penetrated initiating secondary crack continues to propagate in a straight line,and unpenetrated crack propagates in offset;in process of crack propagation penetrating circular hole defect,crack propagation velocity and dynamic stress intensity factor(DSIF)drops rapidly to zero,crack propagation is suppressed,the larger the hole diameter and the nearer the distance to hole,the more significant the suppression action;both initial speed and initial fracture toughness of penetrated initiating secondary crack increase with increase in circular hole defect diameter;in process of interaction between propagating crack and offset circular hole defect,the larger the hole diameter and the smaller the offset distance,the shorter the initial offset distance of crack and the larger the maximum offset,and DSIF and propagation velocity of crack propagation increase a little bit locally;the study results provide a reference for analyzing dynamic crack propagation features and material failure mode.