球墨铸铁行星架断裂原因分析

Fracture cause analysis of ductile iron planet carrier

球墨铸铁行星架在使用过程中发生断裂,断裂位置位于两行星孔之间。通过宏观观察、微观观察、力学性能等分析手段对行星架进行综合研究和分析,确定了行星架的断裂模式为疲劳断裂,疲劳扩展较充分,未发生局部受力过大的现象,开裂位置存在缩松缺陷。缩松缺陷的存在切断了材料内部的连续性,造成断裂部位的强度降低,使得零件在未达到材料的疲劳强度前就萌生裂纹,尤其是受周期性交变载荷的零件。同时,由于材料缩松严重,在零件表面出现,使得零件表面该缺陷位置的应力集中系数急剧增加,过早地萌生疲劳裂纹,造成零件早期疲劳失效。

The ductile iron planet carrier fractured in the process of use,the location of the fracture is between two planet holes.Through the comprehensive analysis of the planet carrier by means of macro analysis,micro analysis,mechanical properties and other analysis,it is determined that the fracture mode of the planet carrier is fatigue fracture,the fatigue expansion is sufficient,no phenomenon of excessive local force was found,and there are shrinkage porosity defects at the cracking position.The existence of shrinkage defects cut off the internal continuity of the material,resulting in the reduction of the strength of the fracture site,make the parts crack before reaching the fatigue strength of the material,especially the parts subjected to periodic alternating load.The shrinkage is serious and produce prematurely extending to the surface of the parts,so that the stress concentration coefficient at the defect on the surface of the part increases sharply,fatigue cracks resulting in early fatigue failure of parts.