厚度与加载速率对铁素体钢断裂韧性影响的SP压杆法实验研究

采用SP压杆实验方法,在常温下研究小圆薄片断裂韧性的厚度效应及加载速率对断裂特性的影响.实验结果表明,随着厚度的增加,断裂变形能增加,断裂部分的外表面因双向应力状态表现出微突起,微突起四周存在微小裂纹;随着加载速度的增加,断裂变形能增加,剪切断裂表面表现出从密集韧窝到韧窝连接成片特征.考虑试件变形过程中不同部分的能量耗散,从SP试件的整体断裂变形能得到试件的断裂韧性的宏观表达,断裂韧性随着厚度的增加而增加,随着加载速度的增加而减少.采用临界塑性断裂应变作为裂纹起裂判据,单位面积的能量耗散率作为裂纹扩展和失效判据的断裂模型,用有限元方法对SP压杆实验进行模拟,得到与实验结果比较相符的模拟结果.

Experimental Study of the Effect of Thickness and Loading Speed on the Fracture Toughness of Ferric Steels Based on Small Punch Test Method

To investigate the thickness effect on the fracture toughness and the loading speed effect on the fracture properties, round thin specimens Small Punch (SP) tests were carried out at room temperature. Experimental results show that along with the increment of samples thickness, SP impact energy increases, fracture surface displays typical ductile fracture, and the punched part is full of half-sphereicl little bulge. Around the bulge there are micro-cracks due to two-axial stress condition. With the loading speed increase, the micro dimples on fracture surface are stretched larger and wider. Take into account the energy dissipation, the ductile fracture toughness is deduced from the SP energy theoretically. The fracture toughness increases along with the increment of the specimen thickness and decreases along with the loading speed increase. The fracture strain and the fracture energy dissipation rate per unit-area criterions are introduced into the continuum damage model, with which the FEA(Finite Element Analysis) simulations get the results of the crack propagation process which agree with the experimental results.