某型机主机匣在振动疲劳试验约60h发现振动值逐渐增大现象,拆卸后检查发现主机匣轴承支座加强筋处开裂,通过宏观分析、断口分析、金相检验、硬度测试、化学成分分析以及力学性能测试等检测手段,确定了主机匣开裂性质和原因。结果表明:主机匣开裂为疲劳开裂,其开裂原因是由于表面存在铸造冷隔或浇不足缺陷,加大了该处的应力集中。建议严格控制铸造工艺,或在铸造过程中厚度方向留一定的裕度,并对其表面进行加工,保证表面的完整性。

Vibrant range increasing phenomenon was found after the core box working for 60 h, and after disassembling it was found that cracking happened at position of the supporting seat reinforcing rib. The cracking feature and cause of the core box were analyzed by means of macro observation, fracture analysis, metallographic examination, hardness testing, chemical compositions analysis and mechanical properties test. The results show that the crack mode was fatigue cracking. The cracking was caused by the cast aluminium freedom interface defect on surface, which increased the stress concentration of the area. It was suggested to strictly control the casting process or to have a certain machining margin in thickness direction to improve the surface integrality of the core box.