针对某型号发动机曲轴疲劳试验未达到规定载荷累计循环次数, 早期疲劳开裂的问题, 采用化学成分分析、力学性能测试、断口分析、金相检验和表面氮化层检验等方法对其进行了失效分析。结果表明: 该曲轴为疲劳开裂, 曲轴过渡圆角处的高应力区存在大尺寸硬质非金属夹杂物是导致曲轴过早疲劳开裂的主要原因; 另曲轴过渡圆角处加工质量差, 使得该处应力集中加剧, 也是致使该曲轴过早疲劳开裂的重要因素。

Methods such as chemical compositions analysis, mechanical properties test, fracture analysis, metallographic examination and superficial nitration case verification were adopted to analyze the engine crankshaft which early fatigue cracked and didn’t reach the required load accumulative total cycling times when fatigue test. The results show that the crankshaft was fatigue cracking. There were some large scale hard nonmetallic inclusions at the transition arc where the stress was rather higher, which was main reason for the early fatigue cracking of the crankshaft.The poor processing quality of crankshaft was also crucial reasons for the early fatigue cracking of the crankshaft.