Effect of cold expansion on fatigue life of double lap structure

Hang Peng,Jianbo Qin,Tianjiao Zhao

doi:10.1051/jnwpu/20213910189

Abstract

The finite element simulation analysis was used to determine the weak parts of the fatigue life of a double lap structure, for which the cold expansion finite element model was established. The effect of the cold expansion of slotted bushings on the residual stress distribution around the hole of the double lap structure under different interferences was deeply studied, and the optimal interference amount was determined to be 2.5%. The effect of reaming on the residual stress distribution around the hole was studied. The residual stress distribution around the edge of the hole under actual loading conditions before and after cold expansion was compared to provide a theoretical analysis basis for extending the fatigue life of the specimen after cold expansion. The China-made and free- forged 7A85 aluminum alloy specimen was used to obtain the fatigue life and DFR value of the double lap structure after ordinary hole making and the cold expansion of slotted bushing. The results show that the fatigue life under 95% confidence and 95% reliability after cold expansion strengthening increases by about 49% and that the tested DFR value increases by about 9.8%.

Highlights

由图 8a)可知,不同挤压量下,切向残余应力沿径向呈现出先增加,再减小,然后再增加,到远端处再减小为零的规律。最大切向残余压应力出现在孔壁处。其中,距孔壁 0 ~ 1 mm 范围内,1%,2.5%以及 2%干涉量下的切向残余压应力较大。
Numerical prediction and experimental verification of fatigue life of TC4 plate strengthened by cold expan⁃ sion[ J]
Journal of Materials Processing Technology, 2007,189(1 / 2 / 3) : 45⁃47

Summary

Introduction

影响,重点研究了开缝衬套冷挤压后铰孔对孔边残余应力的影响,并进行了试验验证;葛恩德等[7] 通过对 TC4 板孔挤压前后的残余应力场进行有限元模拟,探讨了挤压量对孔边应力分布的影响, 得到 TC4 板的最佳挤压量为 4%;曹增强等[8] 针对小边距孔的压合衬套强化工艺进行研究,分析了不同干涉量对孔周的影响,通过施加循环外载,得到了最佳干涉量;霍鲁斌等[9] 通过 TC4⁃DT 钛合金耳片建立了二次冷挤压的数值建模方法并通过实验进行了验证;王洪达[10] 以 TC4 钛合金为研究对象,研究了不同挤压量、初孔直径以及孔边距等参数对孔壁残余应力的影响; Burlat 等[11] 在芯棒外增加了衬套, 研究了不同的挤压量以及外载荷历史幅值对试验件疲劳寿命的影响;Karabin 等[12] 基于 7085⁃T7651 航空铝合金板研究了衬套几何开口形状对孔冷挤压塑形应变的影响。图 5 7A85 铝合金真实应力应变曲线图 6 1Cr17Ni7 不锈钢真实应力应变曲线由图 8a)可知,不同挤压量下,切向残余应力沿径向呈现出先增加,再减小,然后再增加,到远端处再减小为零的规律。最大切向残余压应力出现在孔壁处。其中,距孔壁 0 ~ 1 mm 范围内,1%,2.5%以及 2%干涉量下的切向残余压应力较大。由表 5 可知,冷挤压强化后双 95% 疲劳寿命提升了约 49%,试验 DFR 值提升了约 9.8%。

Results

Conclusion