孔挤压强化对GH4169孔结构高温疲劳裂纹扩展行为影响研究

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.