Study On Multi-axis High Cycle Fatigue Life Of Steering Knuckle Under Random Load

Steering knuckle is one of the key parts in the automobile chassis,which bears the complex road load transmitted by the wheel.Once the steering knuckle is damaged,the consequences can not be estimated.The most important form of failure is fatigue failure,so it is essential to accurately analyze the fatigue reliability of the steering knuckle.Most of the fatigue failures of steering knuckle occur under random load.However,the fatigue analysis under random load is different from the constant amplitude load,and the parts will present multi-axial stress state.Therefore,the common uniaxial fatigue analysis method is not applicable to the fatigue analysis of steering knuckle in principle.At present,the fatigue analysis of automobile chassis components is still dominated by uniaxial analysis.Although some studies have applied the multi-axial fatigue criterion to the fatigue analysis of components,it is only limited to the form of simple load,and there are few reports on the multi-axial fatigue analysis under random load.So this paper studies the general process of multi-axis fatigue analysis of automobile chassis components under random load with the steering knuckle of a B class car as the research object fatigue analysis of steering knuckle is carried out by using six time domain multi-axis high cycle fatigue criteria and two frequency domain multi-axis high cycle fatigue criteria.The prediction rule of amplitude distribution and life expectancy is summarized,and the time domain/frequency domain criterion is evaluated from the aspect of life prediction and calculation efficiency.Firstly,the load collection scheme of the durable road in the test field was designed.The main signals collected were the six component force signals of the wheel core and the signals of the monitoring point.The stone road B with the most obvious damage magnitude was selected as the load basis for this analysis.The multi-body dynamics model of the vehicle was established and verified by measuring parameters including parts quality characteristic parameters,suspension hard point information,mechanical characteristic parameters,four-wheel positioning parameters and vehicle quality parameters,etc.The load spectrum of knuckle joints was extracted by virtual iteration method,and the fatigue hazard point of steering node is calculated and verified by uniaxial fatigue analysis method based on time domain and frequency domain.The time domain multi-axial fatigue criterion was used to analyze the fatigue life of the hazard points,and the critical plane solution and multi-axial cycle counting under random load were studied,and the amplitude distribution law was summarized.The results show that when solving the plane of maximum shear stress amplitude,the maximum variance method is based on statistics.Compared with the other four methods,it has higher efficiency and accuracy,and is more suitable for solving the critical surface under random load.In terms of amplitude distribution and life prediction,the equivalent shear stress amplitude of Zhang-Yao criterion is larger on the whole,and the large stress amplitude of Mc Diarmid criterion only accounts for 3.4%,which is significantly higher than that of other criteria,while the equivalent stress amplitude ratio of Dang Van criterion and Findley criterion in all ranges is close.This paper studies the application method of Von Mises and Zhang-Yao multi-axis frequency domain criterion,predicts the fatigue life of steering knuckle danger point,and evaluates the two criteria from many angles.The comparison Von Mises the power spectral density curve of equivalent force corresponding to the Zhang-Yao multi-axis frequency domain criterion shows that the Von Mises criterion curve is relatively higher,which indicates that the energy value of each frequency of equal effect force is higher.Compared with the amplitude probability density function of equal effect force power spectral density,Von Mises criterion corresponds to smaller cycle times and life prediction criterion Von Mises fatigue analysis results are conservative.The time/frequency criterion is compared and evaluated from two aspects of life prediction and calculation efficiency.The relative error between Von Mises and Zhang-Yao time domain and frequency domain lifetimes is less than 0.71,and there is no unreasonable deviation in the prediction results of time/frequency criterion,which indirectly explains the accuracy of the simulation analysis process.The time-domain method and frequency-domain method are more efficient for multi-axis fatigue analysis under road load with longer load time and fewer channels,and more effective for multi-axis fatigue analysis under road load with shorter load time and more channels.Through the above research,in order to provide reference for automobile chassis parts design and reliability analysis.