Prediction And Evaluation Of Fatigue Life For Automotive Enging Bracket

Among various engineering problems of mechanical parts,fatigue failure of metal structures is an important research topic.In order to improve the reliability of the engine system,accurately predict the fatigue life of the engine bracket,and save test costs,this paper is based on the analysis of the road load spectrum of the test field,combining the mechanical properties and fatigue properties of metal materials,from the aspects of high and low cycle fatigue properties and metal hysteresis effect Verify the fatigue life model and discuss the fatigue failure mechanism of the engine bracket,the main contents are as follows:(1)Preprocess the road load signal collected in the test yard.In the time domain,the over-threshold method is used to extrapolate the working load of the engine mount.Combined with the characteristics of the load signal,the mean and amplitude distribution models are constructed.Complete one-dimensional program load spectrum and two-dimensional program load spectrum of engine bracket.(2)Based on the local stress-strain method,a crack initiation life model of the notched specimen was constructed to determine the characteristics and connections of high-cycle and low-cycle fatigue,and the difference between high-cycle and low-cycle fatigue was analyzed from the perspective of failure mechanism.Modify the initial crack resistance coefficient,construct a weighting function to establish the correlation between high-cycle and low-cycle fatigue,and uniformly consider high-and-low-cycle fatigue.Take 45~#steel and 316L as examples to verify the accuracy and rationality of the fatigue life model,and predict the life of the engine bracket.(3)According to the working conditions of the engine bracket,the load characteristics are discussed,and the static analysis of the engine bracket is carried out.The results of finite element analysis are verified through experiments to determine the danger points of fatigue fracture of the engine bracket.Analyze the test data of engine bracket bench and discuss its failure mechanism.The load correction factor is introduced to predict the fatigue life of the engine bracket based on the amplitude load spectrum.(4)According to the metal anelastic effect,the energy dissipation model is constructed.By analyzing the energy conversion law of the specimen during the fatigue loading process,a fatigue life prediction model based on hysteretic elastic energy is proposed.Under the action of high frequency and low load alternating load,the phenomenon of strain hysteresis stress appears in the metal,and the elastic strain hysteresis causes the mechanical energy to be transformed into hysteresis elastic energy and generates heat dissipation.Take AZ31 magnesium alloy as an example to predict the fatigue life,discuss the applicability of the model,and use this to predict the fatigue life of the engine bracket.In this paper,based on the mechanical characteristics of the engine bracket during fatigue loading,based on the equivalent stress method,energy method,and dynamic elastic modulus characteristics,different life prediction models are proposed.By comparing the test results,the applicability of the model is verified.The research results provide a basis for the fatigue life estimation and fatigue durability bench test of auto parts that bear complex and variable random loads.At the same time,the research method in this paper is also applicable to the fatigue life estimation of other bearing parts or high-speed moving parts and assemblies.