Vibration Analysis And Passive Vibration Reduction Research Of SR20 Engine’s Mounting Bracket

The SR20 is a small piston aircraft produced by Cirrus Design Corporation.The flight training unit already has more than 150 SR20 aircraft and undertakes very busy flight training missions.The aircraft engine mounting bracket is a key component connecting the aircraft and the piston engine.Once it fails,it will directly endanger flight safety.The flight training unit found that a SR20 aircraft engine mounting bracket was broken during the inspection.In the successive inspections,six aircraft engine mounting brackets were found to have cracks.The generation of cracks is often due to the effect of vibration load,which will lead to small deformation and stress concentration in the material,thus causing the generation and expansion of cracks.Therefore,it is urgent to realize the vibration reduction of the engine mounting bracket by laying damping materials.This thesis studies from the following aspects:(1)The non-destructive testing of the engine mounting bracket was carried out.The test results showed that there were cracks in the engines mounting bracket of six SR20 s,and the crack position was found.Considering that the engine mounting bracket will be affected by the vibration of the engine,the vibration source of the engine mounting bracket is analyzed.Through the laser vibration measuring equipment,the vibration test of the engine at different speeds is carried out during the ground test of the aircraft,and the vibration acceleration data of the engine is obtained.The time domain and frequency domain analysis provides the basis for the subsequent harmonic response analysis of the engine mounting bracket.(2)The three-dimensional model of the engine mounting bracket is established,and the modal analysis of the engine mounting bracket is carried out.The natural frequency and vibration mode of the first four orders of the engine mounting bracket are obtained.The modal strain energy analysis of the engine mounting bracket is carried out,and the modal strain energy analysis results are compared with the non-destructive testing results of the engine mounting bracket.It is found that the position of the modal strain energy is consistent with the crack location of the engine mounting bracket.Taking the results of engine vibration test as input,the harmonic response analysis of the engine mounting bracket is carried out,and the excitation response of the engine mounting bracket under the working condition of the engine is obtained.(3)The finite element model of the engine mounting bracket with viscoelastic damping structure is established.The finite element analysis of the engine mounting bracket with damping material is carried out.The natural frequency,vibration mode and response of the engine mounting bracket before and after the damping layer are compared.The influence of the thickness of the damping layer on the vibration characteristics of the engine mounting bracket is studied.(4)The position where the strain energy of the engine mounting bracket is larger is determined as the damping layer laying position.Through the response surface method,the response surface approximation model of the total mass of the damping structure and the amplitude of the engine mounting bracket is established.In order to reduce the amplitude of the engine mounting bracket as the optimization goal,the total mass of the damping structure as the constraint condition,the thickness of the damping structure in the laying area of the engine mounting bracket is optimized.According to the optimization results,the amplitude of the engine mounting bracket before and after optimization is compared to verify the feasibility of the optimization scheme and provide a basis for the subsequent formulation of the vibration reduction scheme.