Research On Fault Diagnosis For Cracked Bolt Used In Diesel Intercooler

Intercooler is an essential part for turbocharged diesel engine.The intercooler is responsible for the high temperature gas cooling,so thermal analysis is an integral part of the design.This paper aiming at the fault of the bolts of intercooler for several diesel generator sets,analysis the fracture,the static strength,and the fatigue strength.The reason of fracture is pointed out,and solutions are presented in this paper.Finally,the difficult problem is solved.The main contents of this paper are as follows:Firstly,the microstructure and fracture morphology of the bolts were observed and analyzed by scanning electron microscopy(SEM).The results show that fracture of bolts were caused by fatigue.Secondly,according to the general rules,the thermal stress of bolts are checked.In order to obtain the thermal stress of the bolt,thermodynamic of intercooler is calculated by applying the first boundary condition which temperature is measured.Finally,the static strength of the bolt is checked considering bolt preload.Results meet the requirements of the static strength.Then,the composite model of vibration and thermal is put forward which explain the fracture reason of bolts.The finite element model of intercooler and bolt is established and verified.The equivalent vibration of excitation source is identified,and dynamic load is analyzed.By using the thermal stress and prestress as the average stress,and the mechanical stress as the wave stress,fatigue strength of bolts is checked.The results show that the fatigue strength of bolts are not meet the requirement.Finally,according to the fatigue strength of the bolts do not meet the requirement,this paper puts forward some improvement suggestions,that the 12.9 grade M12 bolts are replaced by 10.9 grade M14 bolts.After improvement,the failure is satisfactorily resolved.