含中心裂纹梯度纳晶金属的数值模拟

Numerical Simulation of Gradient Nanocrystalline Metals with Central Crack

梯度纳晶金属由于其微观组织的梯度分布,力学属性也呈现梯度变化,这使得其表现出不同于传统均匀材料的断裂行为.利用材料力学参数的梯度分布来表征梯度纳晶金属中晶粒尺寸的梯度变化,并编写ABAQUS和MATLAB脚本程序建立分层有限元模型.通过数值模拟计算了含有初始中心裂纹的梯度纳晶金属在受远端均匀拉应力作用下的裂尖J积分,分别研究了屈服应力梯度、裂纹角度和裂纹长度对金属材料断裂韧性的影响,并与传统粗晶进行了对比.结果表明梯度纳米结构的存在导致梯度纳晶金属内部的中心裂纹两端表现出不同的断裂韧性,小晶粒一侧裂尖的抗裂韧性优于大晶粒一侧裂尖,且屈服应力梯度绝对值越大,两者差距越大.梯度纳晶金属的断裂韧性受中心裂纹角度和长度变化的影响与传统粗晶金属基本一致,同时在晶粒尺寸梯度的作用下梯度纳晶的裂尖J积分略低于粗晶,即整体上拥有更好的抗裂韧性.

Gradient nanocrystalline metal exhibits gradient variety of mechanical properties due to the gradient distribution of its microstructure,which makes its fracture behavior different from that of conventional homogeneous materials.A layered finite element model of gradient nanocrystalline metals is established by using ABAQUS and MATLAB scripts,and the gradient distribution of grain size is characterized by the gradient changes of material parameters.The J-integral of the gradient nanocrystalline metal with initial central crack under the remote tensile stress is calculated by numerical simulation.The effects of gradient rate,central crack angle and crack length on the fracture toughness of metallic materials were investigated separately and compared with those for the coarse grain counterparts.The results show that the presence of gradient nanostructure leads to different fracture toughness of the crack tip inside the gradient nanocrystalline metal.The crack propagation resistance of the crack tip in the smaller grain side is better than that in the larger grain side,and the difference between the two crack tips increases with the increase of the absolute value of the gradient rate.The fracture toughness of gradient nanocrystalline metals is significantly affected by the crack angle and crack length,with the same general tendency as that for the coarse-grained metals.At the same time,under the action of grain size gradient,the J-integral of gradient nanocrystalline is slightly lower than that of the coarse grain counterpart,indicating that the gradient nanocrystalline has better crack propagation resistance.