Simulation Analysis On Loosening Resistance Of Double Nuts And Eccentric Concave-Convex Nuts

The bolted connections structure are widely used in the mechanical structure of automobile engine with its advantages of high reliability,good interchange ability,low cost and reusability.However,in the working process,the bolted connections structure will be subjected to axial load,lateral load,torque load,impact load,temperature load,corrosion action,alternating load and so on,leading to a large attenuation of bolt preload,which is called bolt loosening.The whole engine bolted connections have hundreds of thousands of bolted joints according to different models.Any loose bolted connections may seriously affect the safety of the whole vehicle.Therefore,reliable bolted connections are essential to the engine.The study of bolted connections loosening in engine is beneficial to the safety of crew and normal engine operation.This paper selects finite element simulation research methods and uses finite element simulation software Abaqus to study single-nut,double-nut,and eccentric convex-concave nut structures of M10 8.8-grade 45# steel triangular threads.With the help of Matlab parameterized modeling,this paper establishes finite element models for single-nut,double-nut,and eccentric convex-concave nut structures.This paper studies the effects of different pre-tightening force loading and coupling methods on the pre-tightening effect of single-nut structures,as well as the effects of changing transverse load vibration amplitude,transverse load vibration frequency,axial load distribution ratio,thread surface friction coefficient,support surface friction coefficient,material plastic deformation on the anti-loosening performance of double-nut structures under transverse vibration and the effect of the elastic modulus ratio of bolts and nuts on the thread pair load distribution.This paper also studies the effects of changing transverse load vibration amplitude,transverse load vibration frequency,eccentricity of the convex nut,cone angle of the convex-concave nuts,thread surface friction coefficient,and support surface friction coefficient on the anti-loosening performance of eccentric convex-concave nuts structures under transverse vibration.The simulation results show that for the finite element model of the single-nut structure,the torque method and angle method are more accurate than the cross-sectional pre-tightening load method in obtaining the axial stress with smaller errors.By studying different coupling methods,this paper finds that both the coupling method between the reference point and the nut outer cylindrical surface and the coupling method between the reference point and the bolt head outer cylindrical surface could well simulate the pre-tightening process of the bolt,and the axial forces obtained by both methods are consistent,with small errors between the calculated axial stress values and theoretical axial stress values.For the finite element model of the double-nut structure: under lateral vibration for 6 seconds,when the axial load distribution ratio are 0.76,0.9,and 1.21,the total axial force attenuation rate are 9.8%,7.6%,and 6.2%,respectively;when the transverse load vibration amplitude are 0.1mm,0.2mm,and0.3mm,the total axial force attenuation rate are 5%,6.2%,and 8.1%,respectively;when the thread surface friction coefficient are 0.15,0.2,and 0.3,the total axial force attenuation rate are 5.1%,6%,and 6.2%,respectively;when the support surface friction coefficient are 0.15,0.2,and 0.3,the total axial force attenuation rate are 5.9%,5.6%,and 6.2%,respectively;when only considering the elasticity and elastic-plastic deformation of the material,the total axial force attenuation rate are 6.2% and 7.4%,respectively;when the transverse vibration frequency was 10 Hz,20Hz,and 30 Hz,the total axial force attenuation rate are 6.2% for all frequencies,respectively;when the bolt-nut material elastic modulus ratio are 1,1.5,and 2,the maximum Mises average stress of the first buckle thread unit node on the bolt are 440 Mpa,402Mpa,and 360 Mpa,respectively.For the finite element model of eccentric concave-convex nut structure: under lateral vibration for 6 seconds,when the eccentricity are 0.4mm,0.5mm,and 0.6mm,the total axial force attenuation rates are 6%,5.8%,and 5.9%,respectively;when the cone angles are 76°,77°,and 78°,the total axial force attenuation rates are 6%,5.8%,and 5.9%,respectively;when the transverse vibration amplitudes are 0.1mm,0.2mm,and0.3mm,the total axial force attenuation rates are 5.2%,5.8%,and 6.5%,respectively;when the thread surface friction coefficient are 0.15,0.2,and 0.3,the total axial force attenuation rates are 5.4%,5.6%,and 5.8%,respectively;when the support surface friction coefficient are 0.15,0.2,and 0.3,the total axial force attenuation rates are 5.3%,5.6%,and 5.8%,respectively;when the transverse vibration frequencies are 10 Hz,20Hz,and 30 Hz,the total axial force attenuation rates are 5.8% for all frequencies.