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主起落架完成3倍目标寿命疲劳试验后,进行分解检查时发现上转轴的一个孔边缘及孔内壁出现了裂纹,该上转轴共经历了4倍目标寿命疲劳试验,材料为30CrMnSiNi2A超高强度钢。通过外观检查、残余应力测试、断口宏微观观察、能谱分析、金相检验、硬度测试和化学成分分析等方法,对上转轴的开裂原因进行了分析。采用疲劳断口定量分析方法反推上转轴的裂纹萌生寿命,并给出疲劳裂纹扩展速率与裂纹长度之间的关系曲线。结果表明:该上转轴裂纹的性质为高周疲劳开裂,其裂纹萌生于2倍目标寿命+5个加载谱块之前;上转轴开裂原因与轴孔安装过紧进而承受较大载荷谱应力、源区侧表面损伤和残余应力共同作用有关。通过加强装配过程控制、提高表面处理,上转轴已完成安全寿命试验(即7倍目标寿命)。
The main landing gear to complete 3 times the target life fatigue test, the decomposition inspection found that a shaft hole on the shaft and the inner wall cracks, the shaft has experienced a total of 4 times the target life fatigue test, the material is 30CrMnSiNi2A ultra-high strength steel . The cause of cracking on the upper shaft was analyzed by visual inspection, residual stress test, macro and micro observation of fracture surface, energy spectrum analysis, metallographic examination, hardness test and chemical composition analysis. Using fatigue fracture quantitative analysis method to reverse the crack initiation life of the upper shaft, and gives the relationship between fatigue crack growth rate and crack length. The results show that the nature of the upper shaft crack is high-cycle fatigue cracking, and the crack initiation occurs two times of the target life plus five loading spectra. The reason of cracking on the upper shaft and the shaft hole are too tight to bear the larger load spectrum stress. Area side surface damage and residual stress on the joint role. By strengthening the assembly process control, improve the surface treatment, the shaft has completed the safety life test (ie, 7 times the target life).