含异侧偏置裂纹试件的冲击断裂试验

摘要

利用新型数字激光动态焦散线试验系统,分析了含异侧偏置裂纹有机玻璃(PMMA)试件破坏的时程特性和裂纹尖端扩展过程中的应力奇异性变化.得出该加载条件下试件的断裂韧度约为1.16 MN/m3/2,异侧偏置裂纹间距对试件冲击断裂韧度没有明显影响.一定范围内,异侧偏置裂纹间距越大,裂纹扩展的对称性越明显.贯穿主裂纹的扩展路径上存在一个明显的应力变化转折点,此处裂纹尖端的应力集中程度加强,试件由以拉伸破坏为主过渡为拉伸、剪切复合破坏.次裂纹尖端发生明显应力释放的同时,主裂纹尖端的应力集中明显加强.裂纹扩展过程中,裂纹尖端的动态应力强度因子表现出明显的震荡变化,主裂纹相对于次裂纹裂尖奇异性更强.%Using the test system of digital laser dynamic caustics (DLDC), time-related fractural characteristic and crack tip stress change of PMMA specimens which contained bilateral off-center cracks were analyzed.The fracture toughness of specimens was about 1.16 MN/m3/2 under the loading condition.Intervals of the two bilateral off-center cracks almost had no effect on the impact fracture toughness.In a certain range, symmetric degree of crack propagation was improved while intervals of the two cracks increased.There was a mutational stress point of crack tips during main crack propagation.The degree of stress concentration was enhanced and failure mode was shifted from tensile failure to tensile-shear failure at the point.When the stress of secondary crack tips released, stress concentration of main crack was enhanced.Dynamic stress intensity factors of crack tips changed choppily during crack propagation.Compared to secondary crack tips, main crack tips kept advantage in stress all long.