残余应力场中疲劳裂纹闭合的数值分析

本章基于塑性诱导裂纹闭合原理,通过弹塑性有限元方法对残余应力场中疲劳裂纹扩展过程进行模拟,阐释残余应力场中的裂纹扩展行为。论文阐述了模拟疲劳裂纹扩展的方法、残余应力生成方法和残余应力场中裂纹张开、闭合应力的计算方法。模拟了焊接产生的拉伸控制残余应力场和冷胀孔产生的压缩控制残余应力场中的疲劳裂纹扩展,分析了残余应力对裂纹闭合效应的影响。分析结果表明,与不含残余应力场的情况相比,拉伸残余应力具有抵消裂纹闭合效应、促进裂纹扩展的作用,并得出权函数法不适用于这种条件下的疲劳裂纹扩展分析的结论;而压缩残余应力具有增强裂纹闭合效应、抑制裂纹扩展的作用。通过数值分析研究残余应力场中的疲劳裂纹闭合效应,能够考虑裂纹扩展中外载与残余应力相互作用引起的残余应力变化,有助于理解残余应力对裂纹扩展的作用机理和进行裂纹扩展预测。

Exploring Further Fatigue Crack Closure in Residual Stress Field through Numerical Simulation

Aim.The introduction of the full paper reviews a number of papers in the open literature,including two by Li Yazhi et al,and then,in the second half of its second paragraph,outlines the core of our further exploration.Sections 1,2 and 3 explain the method of our further exploration.The core of section 1 establishes the finite element(FE) models of the middle cracked tension specimen and the central hole specimen respectively.Section 2′s core explains the crack growth simulation and then determines the crack opening/closing points.Section 3’s core introduces into the FE models the tension-dominated welding residual stresses directly and the compression-dominated residual stresses by FE analysis of the cold expansion process.The numerical simulation results,given in Figs.6 through 11,and their analysis demonstrate preliminarily that:(1) the tensile residual stress mitigates the crack closure effect by reducing the crack opening/closing load levels,compared with the crack opening/closing load levels that have no initial residual stresses,thereby boosting the crack growth;the weight function method is no longer valid for the stress intensity and fatigue crack growth analysis;(2) the opposite is true for the compressive residual stress,in that it enhances the crack closure effect;(3) the numerical simulation of crack propagation has the advantage of naturally incorporating the residual stress variations resulting from the crack growth and the interaction between the external loading and the residual stresses,thus helping us to understand the mechanism of crack-driving force in residual stress fields.