2024-T351铝合金搅拌摩擦搭接焊接头疲劳性能与寿命预测

通过实验观察2024-T351铝合金搅拌摩擦搭接焊接头焊缝附近区域的焊缝横截面形貌及金相组织。观察表明搅拌摩擦搭接焊接头前进侧与后退侧存在形状不对称的钩状缺陷。将搅拌摩擦搭接焊接头在MTS材料实验机上进行恒幅疲劳加载,得到名义应力幅S-N曲线。根据实验结果建立搭接接头的弹塑性有限元模型,利用SWT疲劳损伤公式和应力集中区域循环应力应变有限元分析结果数据,预测搭接接头疲劳寿命,并将寿命预测结果与实验结果进行对比。结果表明:在低周疲劳寿命范围内,采用SWT疲劳损伤公式对搅拌摩擦搭接焊接头的预测结果与实验结果接近,误差均在2个因子内,但对高周疲劳寿命的预测结果存在较大误差。分析表明,搭接接头的应力集中程度比有效厚度对疲劳寿命的影响更大。

Fatigue Performance and Lifetime Prediction of 2024-T351 Aluminum Alloy Friction Stir Lap Welded Joint

The cross section morphology and metallographic structure in the weld zone of the 2024-T351 aluminum alloy friction stir lap welded joint was observed by experiment.It indictated that there are asymmetric hook-shaped defects on both the advancing side and the retreating side of the friction stir lap welded joint.Friction stir lap welded joints were tested under constant-amplitude fatigue loading on MTS test frame to obtain the S-N curve of nominal stress amplitude.The elastic-plastic finite element model of lap joints was established according to the test.Using the SWT fatigue damage equation and cyclic stress strain data of stress concentration region from finite element analysis,the fatigue lives of lap joints were predicted,and further compared with the experimental results. The results show that the prediction results for the low-cycle fatigue lifetime of friction stir lap joints by the SWT fatigue damage formula are close to the experimental results,and the errors are all within 2 factors,while large error is in the prediction results for the high-cycle fatigue lifetime.At the same time,it shows that the stress concentration of lap joints has greater influence on the fatigue lifetime than the effective thickness.