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某液压缸盖紧固用螺钉在进行试验时发生断裂。采用外观检查、断口宏微观观察、金相检验和硬度测试等方法对两枚断裂失效螺钉进行了分析。结果表明,螺钉A失效性质为过载断裂,其断裂原因主要与装配时拧紧力过大从而产生了扭转剪切开裂损伤有关;螺钉B失效性质为疲劳断裂,其断裂原因主要与螺钉B表面存在脱碳层导致疲劳强度大幅降低有关,且在装配时发生倾斜,螺钉一侧存在附加拉应力,对疲劳失效也有一定的促进作用。建议严格控制热处理工艺和装配过程力矩大小,并加强螺钉孔和螺钉的加工精度控制。
A hydraulic cylinder head captive screw ruptured during the test. The fracture failure screws were analyzed by visual inspection, macro and micro observation of fracture surface, metallographic examination and hardness test. The results show that the failure characteristic of screw A is overload fracture, and the reason of fracture is mainly related to the excessive tightening force during assembly, which leads to torsional shear failure. The failure characteristic of screw B is fatigue fracture, and the fracture reason is mainly related to the surface of screw B The carbon layer causes a significant decrease in fatigue strength, and tilts during assembly, with additional tensile stress on one side of the screw, contributing to fatigue failure. It is recommended to strictly control the heat treatment process and assembly process torque, and to strengthen the screw hole and screw machining accuracy control.