| As an important part of carrying damping fluid and piston rod,the front shock absorber cylinder is one of the important components of vehicle damping system.The shock absorber cylinder constantly bears the impact from the complex road load.Once the fatigue failure occurs,it will directly affect the safety and smoothness of the whole vehicle.In this paper,the fatigue life of front shock absorber cylinder is studied,which focus on five aspects: the compilation of interval load spectrum,the fatigue life prediction of energy method,the durability test and life prediction of shock absorber cylinder,the crack initiation size prediction of cylinder and the fatigue reliability analysis of cylinder.The main contents can be summarizedas follows:(1)Based on the road load signals collected in the test yard,the pre-processing is performed,such as the abnormal value elimination,signal denoising.Considering the load signals fluctuate within a certain error range,the collected load signals are converted into interval load signals by Bootstrap error circle method.The peak-over-threshold extrapolation method is improved by considering the large impact load of special pavement,and the time domain extrapolation of interval load signals is realized.The frequency statistics of interval load signals is counted by rainflow counting method.According to the distribution characteristics of mean and amplitude for loads,the two-dimensional joint distribution model of mean and amplitude is constructed by the extreme value distribution and mixed distribution model.And based on the two-dimensional joint distribution model of mean and amplitude,the one-dimensional and two-dimensional interval load spectrum of shock absorber cylinder are constructed by the equal interval method and non-equal interval method.(2)According to the relationship between static toughness and fatigue toughness in fatigue failure process,baesd on the plastically deformed energy at the crack tip is proportional to crack length,the quantitative model of total dissipated plastic strain energy(TDPSE)and fatigue life is established.At the same time,considering the influence of surface processing on fatigue life,the method of fatigue life prediction of TDPSE is modified.In addition,the TDPSE method and modified TDPSE method are used to predict the fatigue life of Non-Masing materials and Masing materials,respectively.The reliability of modified TDPSE method is verified by comparison with the test results.(3)Based on the load of shock absorber cylinder during driving,fatigue durability test are performed under longitudinal and lateral forces,respectively.The test results are analyzed,and the S-N curve of cylinder under longitudinal and lateral force are fitted,respectively.At the same time,the life predicted by the modified prediction model is compared with that by energy method and test results.Among them,when predicting the fatigue life of cylinder under the lateral force,a more accurate mean stress life model is confirmed by verifying and analyzing the three mean stress life models.In addition,based on the S-N curve of materials and constructed one-dimensional and two-dimensional interval load spectrum,the life of cylinder is predicted,and the one-dimensional and twodimensional interval life spectrum and interval damage spectrum of shock absorber cylinder are obtained.(4)According to the development of macroscopic cracks,the critical dimension criteria of fatigue crack initiation is described.Based on the elastic-plastic fracture mechanics,the short crack fatigue life is studied.Considering the cumulative damage rule of crack initiation life,considering the cumulative damage rule of crack initiation life,the calculation model of fatigue crack initiation size is established.The fatigue failure of 40 steel is taken as an example,based on the comparison with prediction of initiation size by the constant stress intensity factor threshold method,the feasibility of initiation size prediction by the elasticplastic fracture mechanics method is verified.In addition,based on the elastic-plastic fracture mechanics method,the crack initiation size of the shock absorber cylinder is predicted.(5)Considering the errors during processing of shock absorber cylinder,to calculate the interval reliability of cylinder,the interval analysis algorithm is introduced into the stressstrength interference model.According to the obtained interval reliability,based on the dispersion coefficient method,the safety life of shock absorber cylinder can be predicted,and which can lay a technical foundation for its reliability and durability evaluation.The research results of this paper can provide theoretical basis for fatigue life prediction of automobile parts under complex random loads,and also lay a technical foundation for the design and durability evaluation of similar products.Based on the influence of surface roughness on life,the fatigue life prediction method is modified. |
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