压杆法研究厚度对小圆片试样断裂韧性的影响

SMALL PUNCH TEST ASSESSMENT FOR THE EFFECT OF THICKNESS ON THE FRACTURE TOUGHNESS OF THE SMALL SPECIMENS

采用SP压杆实验方法,在常温下对六种不同厚度的小圆薄片的断裂韧性进行测试。实验结果表明,随着厚度的增加,断裂变形能和断裂韧性增加,断裂部分的外表面表现出微突起,微突起四周存在微小裂纹明显的特征。考虑弹塑性变形能,通过SP冲压断裂变形能计算得到断裂韧性,进而得到临界断裂变形能密度。采用塑性断裂应变作为裂纹起裂判据,临界断裂变形能密度作为裂纹扩展判据的断裂模型,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。采用GTN模型研究厚度对空洞增长的影响,得到厚度增加导致微突起明显的空洞率增加。

Small Punch （SP） tests have been carried out at room temperature on small specimens with six kinds of thicknesses. Experimental results show that the SP fracture energy and the fracture toughness increase with the thickness of the samples. The fracture surface displays the typical ductile fracture, and the outer surface of the half-sphere part cut off by the punch is full of bulgings around which there are micro cracks. From the micro mechanics of the energy dissipation, the ductile fracture toughness is deduced from the SP fracture energy theoretically. The fracture strain and the fracture energy density dJ＊/dt criterions are introduced into the damage model, with which the Finite Element Analysis simulations get the results of the crack propagation process which agrees with the experimental results. Simulations with Gurson-Tvergaard-Needleman model explain the bulgings on the half-sphere part surface of different thickness.