Failure Anlysis Of Body Of Electronic Unit Pump And Finite Element Calculation

Fracture and cracking occurred on numerous diesel engine unit-pumps during the trial test. The fracture or cracking location of failed unit-pumps are all situated at the oiling-end of pump-body. In this study, two failed unit-pumps (one fractured completely, and another cracked) were investigated. The fracture surfaces and crack morphology of two failed unit-pumps were observed by visually and scanning electron microscopy (SEM) to asses failure mechanism and failure causes. The macro-and micro-structure were observed by SEM. The surface hardness, matrix hardness and micro-hard ness profiles of nitrided layer on the oiling-end of unit-pump were evaluated. The influence of The forging, metallurgical, factors, et on the failure of unit-pumps were discussed. The stress field distribution at different fillet radius of internal hole of oiling-end and pre tightening The influence of the construction of oil-end of unit-pump and pretension location of thread on the stress distribution were simulated by ANASYS software. The relation of stress field distribution at oiling-end and failure of unit-pump were discussed. Based on the ANSYS software and the service condition of electronic unit-pump, stress concentration coefficient with different fillet radius ofoiling-end were calculated. By analyzing comprehensively the simulation results and related datum, optimum fillet radius and pretension location of thread can be obtained.The main conclusions of the paper are as follows:(1) Over-small fillet radius of internal hole of oiling-end for failed two unit-pumps is mainly responsible for the failure of the two unit-pumps, which leads to severe stress concentration. Severe porosity in the compound layer and presence of network-like nitrides in the diffuse layer facilitate crack initiation and propagation. Crack initiated at the 1st fillet of internal hole of oiling-end of unite-pump and fatigue fracture is failure mechanism. Fillet root of internal hole is same level position with the groove of 5th thread, and 5th thread is just corresponding to the 1st num of oil-pipe (pretension location). Therefore adding stresses make the crack propagate rapidly and lead to premature fatigue fracture.(2) Finite element analysis (EFA) results show that the fillet root of internal hole unit-pump is stress concentration zone. (3) FEA results indicate that failure possibility can be decrease in effect by controlling two variables (fillet radius of internal hole and pretension thread No.). Increasing fillet radius can significantly decrease stress concentration degree and reduce stress concentration coefficient. And increase pretension thread No. also decrease stress concentrate degree. FEA simulation gives 78% an optimize combination of fillet radius and pretension thread No. (R=3.5mm, pretension thread:8th thread).