Research On Fracture Analysis Method Of Automobile Bolt Fasteners Fracture Failure

In China,as the demand for automobiles increases year by year,automotive manufacturers continue to expand their product range and output to meet the market demand.It is the direction of automotive manufacturers to improve production efficiency and quality.In automotive assembly operations,fasteners connections are one of the important factors that constrain production efficiency and quality.Most bolt fasteners are failed with load-carrying ability caused by fracture.Efficient analysis of the failure causes of bolt fasteners is a significant way to improve the production efficiency and product quality of automobiles.Failure analysis of bolts is complex and comprehensive,and fracture analysis is the focus of bolt fracture failure analysis.The fracture of the broken part records the whole process of crack initiation and extension to final fracture,which is the most information of fracture failure.Instrumentation equipment can be used to obtain information from the fracture and determine the connection between the cause of the fracture and the design,material,process and environment.This paper studies the four common automotive bolt fracture failure cases by fracture analysis method.Combined with force analysis and material analysis,the effectiveness of fracture analysis in the automobile bolt fasteners failure is verified,so that the fracture failure analysis of bolt fasteners can be realized quickly and effectively.The main research contents and results are as follows:The root cause of the engine intake camshaft fixing bolt failure and the central floor tunnel bolt failure are studied by using the fracture analysis method.The macroscopic analysis of the fracture shows that the bolt has no plastic deformation,the fracture is flat,and the radial pattern on the fracture surface expands outward with the inclusions as the center.Microscopic analysis of the fractures confirmed that the inclusions were mainly composed of non-metal oxides such as alumina and calcium oxide.The root cause of the bolt fracture is too many non-metallic inclusions in the bolt base material,which reduces the strength of the bolt and causes abnormal breakage during assembly tightening.The root cause of the bolt connecting the motor and the chassis failure are studied by using the fracture analysis method.Through the macroscopic analysis of the fracture,the plastic deformation of the bolt is observed,and the bolt tightening marks are not uniform.Combined with the microscopic analysis of the fracture,the bolt is fractured with reverse bending fatigue,which is caused by insufficient tightening process during assembly.Fracture analysis of the engine cylinder cover bolt breakage failure case is carried out.By the fracture analysis,the bolt stuck during the tightening process,and the bolt is not properly tightened and resulting in overload fracture during the disassembly.