超声表面滚压加工纯钛梯度材料的力学性能反演与有限元分析

Inversion and Finite Element Analysis of Mechanical Properties of Pure Titanium Gradient Material by Ultrasonic Surface Rolling Processing

对TA2纯钛进行超声表面滚压加工,研究了其截面显微组织和残余应力分布;采用纳米压痕试验测定距表面不同距离处的载荷-压入深度曲线并反演得到应力-应变曲线,将该应力-应变关系作为材料属性,采用有限元方法模拟得到载荷-压入深度曲线,通过与试验曲线进行对比对反演方法进行验证,并且研究了初始屈服应力和应变硬化指数对载荷-压入深度曲线的影响。结果表明:试样表层形成晶粒尺寸逐渐增大的梯度结构,残余压应力随着距表面距离的增加先增大后减小;载荷-压入深度模拟曲线与试验曲线基本一致,最大压入深度的相对误差在8%以内,说明反演方法可靠;随着初始屈服应力和应变硬化指数增大,载荷-压入深度曲线加载段曲率增大,塑性功与总功之比减小,初始刚度变化不明显。

Ultrasonic surface rolling processing was conducted on the pure titanium TA2,and the microstructure and residual stress distribution on cross section were studied.The load-indentation depth curves at different distances from surface were measured by nanoindentaion tests,and then the stress-strain curves were obtained by inversion.With the stress-strain relationship as the material property,the load-indentation depth curves were simulated by the finite element method,and were compared with the test curves to verify the inversion method.The influence of the initial yield stress and strain hardening exponent on the load-indentation depth curves was investigated.The results show that a gradient structure with gradually increasing grain size was formed in the sample surface layer,and the residual compressive stress increased and then decreased with increasing distance from surface.The load-indentation depth simulation curves were basically consistent with the test curves,and the relative errors of the maximum indentation depth were within 8%,indicating the inversion method was reliable.With increasing initial yield stress and strain hardening exponent,the loading curvature of the load-indentaion depth curves increased,the plastic work to total work ratio decreased,and the variation of the initial stiffness was not obvious.