7075铝合金扭转微动疲劳行为研究

Torsional Fretting Fatigue Damages of 7075 Aluminum Alloy

在基于多轴疲劳试验机上自主设计的扭转微动疲劳装置上,对7075铝合金材料进行了扭转微动疲劳试验,讨论了相同法向载荷下不同扭转切应力对扭转微动疲劳寿命的影响,建立了7075铝合金扭转微动疲劳S-N曲线,并采用SEM,EDS,EPMA等分析方法对扭转微动疲劳的损伤区域进行了分析,建立了扭转微动疲劳混合区接触表面损伤和裂纹萌生及扩展的物理模型,揭示了7075铝合金扭转微动疲劳的损伤机理.试验结果表明:微动作用导致疲劳寿命大大降低;扭转微动疲劳S-N曲线呈"ε"型曲线特征;损伤区靠加载端位置氧化严重,氧化程度随着循环次数增加而增加;微动疲劳的裂纹萌生于次表面,接触区中心两侧主裂纹扩展交叉后垂直于接触表面扩展至试样断裂.

The torsional fretting test of 7075 aluminum alloy was carried out on the independently designed fretting fatigue test rig based on the multi-axis fatigue testing machine.The effects of different torsional shear stress on fretting fatigue life under the same normal load were discussed and S-N curve for the torsional fretting fatigue of 7075 aluminum alloy was obtained.The damage regions of torsional fretting fatigue were analyzed based on scanning electron microscopy,energy dispersive spectroscopy and electron probe micro-analyzer.The damage physical model of the surface damages,the crack initiation and propagation in mixed fretting regime was set up to reveal the damage mechanism of torsional fretting fatigue.The experimental results show that the fatigue life was greatly reduced for the effect of the fretting;the S-N curve of the torsional fretting fatigue presented the characteristics of＂ε＂curve.The oxidation of the damage regions near the loading end was the most serious and the oxidation degree of the contact area increased with the number of cycles increasing.The torsional fretting fatigue cracks initiated in the subsurface and the main cracks on both sides of the contact central area propagated,crossed and then continued propagating perpendicularly to the contact surface until the test sample was fractured.