近似二维应力状态下I_1断裂准则假设有效性的试验验证

Experimental Validation of I_1 Fracture Criterion Assumption under Approximate Biaxial Stress Condition

I_1断裂准则假设是基于原子间相互作用模型和断裂物理过程分析提出的一个新的断裂准则,该准则认为,对于完整材料和含缺陷材料,当局部区域的应力第一不变量I_1达到临界值Ib时,材料发生断裂,临界值Ib定义为断裂强度。利用该准则与Mises屈服准则,可给出材料的四种基本力学行为判据,包括弹性变形、塑性变形、脆性断裂与塑性断裂。为验证近似二维应力状态下I_1断裂准则假设的有效性,设计了液压-轴向拉伸联合作用下的薄壁圆管双向应力试验并针对304不锈钢、10Ni5CrMoV钢和EH50钢三种材料开展了试验研究,试验结果表明,对于同一种材料,在不同应力组合下断裂时的第一主应力和第二主应力满足线性关系,应力第一不变量I_1保持恒定,材料存在特定的断裂强度Ib值,从而验证了近似二维应力状态下I_1断裂准则假设的有效性。

I1 fracture criterion assumption is a newly developed fracture criterion based on atomic force model and fracture process analysis. In this criterion,material begins to fracture when first stress invariant I1 of material local region reaches critical value Ibwhich is defined as fracture strength. Based on this fracture criterion and Mises yield criterion,four basic mechanical behaviors criterions are proposed,including elastic deformation,plastic deformation,brittle fracture and ductile fracture. To confirm the validity of the newly developed I1 fracture criterion assumption under biaxial stress condition,internal hydraulic pressure-axial mechanical tension combined loading experiment with thin-walled tube specimen is designed. Test results of 304 austenite stainless steel,10Ni5CrMo V steel and EH50 steel show that for the same material,a linear relationship exists between first principal stress and second principal stress. The first stress invariant I1 remains almost constant when fracture occurs in different biaxial stress states,indicating the presence of fracture strength Ib. Therefore,the validity of I1 fracture criterion assumption in description of fracture process of material under approximate biaxial stress condition is confirmed.