Study on small fatigue crack initiation and growth for friction stir welded joints
Study on small fatigue crack initiation and growth for friction stir welded joints
复制标题
搅拌摩擦焊接头微小疲劳裂纹萌生和扩展研究
DOI：
10.1016/j.msea.2018.10.002
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发表时间：
2019-01-02
期刊：
影响因子：
6.4
通讯作者：
Chen, Shujun
中科院分区：
文献类型：
--
作者：
Sun, Guoqin;Wang, Chongwen;Chen, Shujun
采用复型技术研究了7075铝合金搅拌摩擦焊接头疲劳小裂纹的萌生和扩展行为。研究了在不同加载应力水平下，显微组织对小裂纹萌生和扩展的影响。试验结果表明，小裂纹的萌生和扩展主要受强化颗粒、晶界、粗糙坑和硬度分布的影响。当应力比为0.1时，当循环次数小于疲劳寿命的20%时，小裂纹开始扩展。当应力比降低到-0.3时，小裂纹扩展到疲劳寿命的30-45%。小裂纹萌生和扩展阶段约占疲劳寿命的50-80%。在小裂纹扩展阶段，主裂纹的扩展速率与其它小裂纹的扩展速率相似。在长裂纹扩展阶段，主裂纹的扩展速率远大于其它小裂纹的扩展速率。接头不同区域的显微组织对断裂模式有影响。
Small fatigue crack initiation and growth behavior for 7075 aluminum alloy friction stir welded joints are investigated with the replica technique. The effects of microstructure on the initiation and propagation of small cracks are studied under different loading stress levels. The test results show that the initiation and propagation of small cracks are mainly affected by strengthening particles, grain boundaries, rough pits and hardness distribution. Small cracks begin to grow when the cycle numbers are about less than 20% of the fatigue life at the stress ratio of 0.1. With the decrease of stress ratio to - 0.3, the small cracks grow until the cycle numbers are about 30-45% of the fatigue life. The phase of small crack initiation and propagation accounts for about 50-80% of the fatigue life. The growth rate of the major crack is similar to that of other small cracks in the stage of small cracks growth. In the stage of long cracks growth, the growth rate of the major crack is far greater than that of other small cracks. The microstructures of different regions of the joint have an effect on the fracture mode.