7075铝合金喷砂表面残余应力在疲劳过程中的松弛规律
Relaxation Rule of Residual Stress on Shot-peening Surface of 7075 Aluminum Alloy During Fatigue
胡永会, 吴运新, 郭俊康
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作者单位：中南大学 机电工程学院, 湖南 长沙 410083
中文关键字：喷砂强化； 残余应力； 疲劳； 应力松弛； 疲劳累积损伤
英文关键字：shot peening; residual stress; fatigue; stress relaxation; fatigue cumulative damage
中文摘要：对7075高强铝合金进行喷砂强化，采用X射线衍射法研究循环载荷作用下疲劳过程中喷砂表面残余应力的松弛规律。结果表明，残余应力的松弛主要发生在疲劳过程开始的100个周期内， 其中大幅度松弛发生在初始10个周期内， 1000次循环后残余应力基本稳定。不同应力水平下的松弛行为表明，循环应力达到疲劳极限以上时，残余应力松弛的幅度和速率都较大。经过150 ℃ × 2 h保温处理的试样其表面残余应力显著降低，且疲劳过程中应力松弛的幅度和速率都降低。表面喷丸或喷砂强化试样大多在表面强化层下的拉应力区域产生裂纹，疲劳累积损伤理论也表明疲劳损伤是可以累加的，故表面存在一定数值的残余压应力并不能说明试样没有发生疲劳损伤，工程上不能只依据表面残余应力来判定材料的疲劳性能。
英文摘要：Surface shot-peening treatment of 7075 high-strength aluminum alloy was carried out and the relaxation rule of residual stress on the surface of shot-peening specimens was determined by X-ray diffraction method during cyclic loading fatigue. The results show that significant relaxation of residual stress occurs during the first 10 to 100 cycles, and stresses remain to be steady after 1000 cycles. Larger cyclic loading can cause greater value and rate of residual stress relaxation. In addition, surface residual stress of shot-peening specimens treated at 150 ℃× 2 h has a great decrease. Fatigue cracks of surface-strengthened specimens often initiate at tensile area below surface strengthening layer, and fatigue cumulative damage rule also shows that fatigue damage is accumulative. Therefore, components may be fatigue-damaged when the surface residual stress is compressive, so material fatigue performance cannot be determined only by surface residual stress in practice.