孔挤压强化对GH4169孔结构高温疲劳裂纹扩展行为影响研究

Effects of cold expansion process on high temperature fatigue crack growth behavior of GH4169 hole structure

关键词:  镍基高温合金  冷挤压  残余应力  疲劳裂纹扩展  应力强度因子

Key words:  Nickel-based high temperature alloys  Cold expansion  Residual stress  Fatigue crack growth  Stress intensity factor

摘要:

为探究孔挤压强化对镍基高温合金GH4169孔结构疲劳裂纹扩展行为的影响规律，针对孔挤压强化后螺栓孔特征模拟件开展残余应力松弛及疲劳裂纹扩展试验。结果表明，经热松弛稳定后，孔边依旧可以保持至少400 MPa的残余压应力水平，且孔壁表面残余应力松弛幅度高于内部；孔挤压强化后疲劳裂纹扩展速率降低一个数量级，随着相对挤压量增加，疲劳裂纹扩展速率降低幅度增大，疲劳裂纹扩展寿命增幅为4~22倍。结合有限元仿真及断口分析，孔挤压强化对疲劳裂纹扩展的影响机制可归结为松弛至稳定后的残余压应力抵消部分外载应力，导致有效应力强度因子范围减小，使得疲劳裂纹扩展速率降低。基于该机制，利用残余应力修正的Walker模型对疲劳裂纹扩展寿命进行预测，误差在1.8倍分散带以内。

Abstract:

In order to explore the fatigue crack growth performance of the GH4169 nickel-based superalloy cold expansion holes， the residual stress relaxation and fatigue crack growth experiments were carried out on the bolt hole plate specimen after cold expansion in this work. The results show that the hole edge can still maintain a residual compressive stress level of at least 400 MPa after thermal relaxation is stabilized， moreover， the residual stress relaxation amplitude on the surface of the hole wall is greater than that inside. The fatigue crack growth rate of cold expansion holes is reduced by one order of magnitude， and as the relative expansion rate increases， the fatigue crack growth rate is further inhibited. Meanwhile， fatigue crack growth life of cold expansion holes increases by 4 to 22 times. Combining the finite element method and fracture analysis， the effect mechanism of cold expansion process on fatigue crack growth can be attributed to the fact that the stable residual compressive stress offsets part of the external load stress after thermal relaxation， which leads to a reduction in the effective stress intensity factor range， thereby inhibiting the fatigue crack growth rate. Based on this mechanism， the Walker model modified by residual stress is used to predict the fatigue crack growth life， and the error is within 1.8 times the dispersion zone.