托板螺母自锁失效原因探讨

Failure Analysis on Auto-lock of Plate Nut

针对一起飞机托板螺母自锁失效问题,开展螺母收口形态对比观察、组织结构分析以及硬度测试。结果表明:托板螺母自锁失效属于收口段金属材料的松弛变形失效。螺母组织均匀性较差,特别是材料表层存在粗大晶粒组织,残余奥氏体含量较高,对抗应力松弛不利;收口形态一致性差,导致螺母装配受力不均;二者是导致螺母个别出现松弛失效的直接原因。提出了在自锁螺母的研制生产中应重点关注材料组织均匀性、收口一致性、螺栓尺寸合理性以及服役环境下的组织稳定性。

Auto-lock failure occurred to a plate nut in an aircraft.In order to find out the failure cause,macro observation,structure examination and hardness testing were carried out.The results show that the auto-lock failure of the nut was because of the relaxation deformation of the material at the narrowing mouth.The poor microstructure uniformity of the nut,especially the large grains near surface,and a larger amount of residual austenite resulted in the low resistance to stress relaxation.And the poor consistency of the shape and size of the narrowing mouth led to uneven assembly stress.The above two factors directly led to the relaxation failure of the nut.Accordingly,it is proposed that more emphasis should be placed on the following aspects during the manufacturing process of the plate nuts:uniformity of microstructure,shape and size consistency of narrowing mouth,size appropriateness,and microstructure stability under service environment.