Fatigue Analysis Of A Heavy-duty Commercial Vehicle’s Fender Bracket Based On Virtual Iteration

Nowadays,automobile manufacturers and consumers have paid increasing attention to fatigue durability,which is an important index to evaluate automobile performance.Aiming at precisely predicting fatigue life for fender bracket of a heavy-duty commercial truck,a fatigue life analysis method based on virtual iteration is presented,and the results of simulation are validated by the real durability test.The major research works in this paper are as follows:(1)The finite element model of a partial frame that contains the fender bracket is built,and modal analysis is proceeded using the Lancozs method to obtain the modal parameters and modal stress;Based on the fixed interface modal synthesis method and ADAMS,a seven degree of freedom virtual test rig with flexible fender baraket model is developed.(2)The acceleration signal of a circel of endurance road testing is measured;all the test signal is pretreated and edited,including spike filter,drift correction,interception,resampling and Fourier filter.According to the spectral characteristics of different road sections,differential filtering strategy is introduced to effectively preserve the characteristics of each section.(3)Based on the seven DOF virtual test rig with flexible fender baraket model,the tentative iteration is carried out,and the accuracy of the virtual iteration method and the iteration model is verified;The virtual iteration is carried out respectively according to test signal of the different road sections,it is found out that the error is allowable,besides,the specific factors that affect the quality of virtual iteration are analyzed.(4)The boundary load spectrum and the dynamic stress history of the fender braket are obtained based on the virtual iteration results;under the load of cobble stone,the differrence of fatigue results based on nominal stress method and local stress-strain method is compared;Also the effects of quasi-static method and modal stress recovery method(MSR)on fatigue simulation results are studied;The results show that the local stress-strain method is more suitable to predict the fatigue life of the fender bracket and the modal stress recovery method considering the structural resonance effect is more conservative and accurate.(5)Using MSR method and local stress-strain method,the fatigue life prediction of fender braket under the load of endurance road testing is carried out,the subsequential vehicle durability test shows that the simulation results have high accuracy,which verify the effectiveness of the method of fatigue analysis based on virtual iterationThe results of this study provide a basis for anti-fatigue optimum design of fender bracket.Meanwhile,the research methods of this paper can also be used for fatigue life analysis and structure optimization of other parts of the vehicle.