Aircraft Engine Mounting Frame Welding Stress Analysis Based On SYSWELD

The engine mounting frame is the key connecting part between the fuselage and power device of a piston aircraft,which needs to transfer the thrust and torque of the engine to the aircraft during normal flight.The component needs to bear the vertical and lateral loads of the engine and the severe vibration of the propeller during its service.Once the structural failure of the component occurs,the flight safety will be endangered.A flight training unit found cracks in the welded joints of one cirrus SR 20 aircraft engine mounts during routine inspection,and later found cracks in the welded joints of six of the aircraft engine mounts at the same location during further inspection.After preliminary investigation,the engine mounting frame of this type of aircraft has no repair process that can be implemented.Once such problems occur,the parts can only be purchased from abroad for replacement,which has a long cycle and high cost and directly affects the normal flight training aircraft.This topic is proposed under the above background,to find out the cause of failure and develop the autonomous repair process,so as to save the funds of the flight training unit and meet the needs of continuous airworthiness support for the current cirrus SR 20 aircraft.Firstly,the material composition analysis of the cirrus SR 20 aircraft engine mounting frame was carried out,and the material of the mounting frame was determined to be ASTM4130 high strength alloy steel.The fracture analysis of the main pipe and branch pipe shows that the failure of the mounting frame is caused by welding microcrack caused by welding residual stress.In the case of aircraft under various loads,cracks grow until fracture,improper control of welding process will lead to residual stress concentration,and finally produce welding cracks.Therefore,it is very important to improve the welding process parameters and minimize the residual stress in the welding joint area,so as to improve the mechanical properties of the welding joint,to avoid the occurrence of welding cracks.Then,SYSWELD software was used to conduct numerical simulation of the T-tube welding joint of the aircraft engine mounting frame with reference to the existing process,and the temperature and stress fields of TIG and ARC welding were calculated.The cloud map of the model confirmed that the fracture location was the concentrated area of welding residual stress.Then X-ray test was carried out to test the welding residual stress and verify the correctness of the simulation results.By comparing the residual stress of TIG and ARC welding,it is concluded that TIG is better than ARC welding in this subject.Then the single factor control method is used to optimize the welding process by exploring the influence of welding current,welding speed and preheating temperature on residual stress.Finally,the optimized welding process is applied to the simulation of welding and repair of the whole mounting frame to explore the distribution of residual stress after welding and repair and the deformation of the whole structure,which provides a certain reference for the actual welding and repair process and lays a foundation for the development of independent welding and repair process.Through a series of tests and simulations,it is concluded that the primary cause of the failure of the welded joint of the aircraft engine mounting frame is the concentration of welding residual stress.The residual stress of TIG applied to this topic is less than that of ARC welding.The values of welding current,welding speed and preheating temperature have significant influence on the residual stress after welding.The simulation results show that the optimized welding process can reduce the residual stress and control the deformation of the whole structure.