| Front axle is one of the most important parts of automobile chassis. Its loads are complex. It is one of the key components to automotive safety performance. At present, fatigue damage problem of the axle becomes increasingly outstanding. Many traffic accidents are caused by it. So its reliability of strength and life has important effects on vehicle driving safety.In this paper, the finite element analysis is carried out on the front axle of some heavy duty truck, which provides certain theoretical basis for the design and production. And the fatigue problem with damage crack of the front axle is studied. The following is the main research work.(1) Strength analysis of various conditions. Based on the structure and mechanical characteristics of the front axle, the geometric model is reasonably simplified and modified. Then the finite element model is established. The load conditions of three kinds of working conditions include full load, braking and sideslip are analyzed to determine the loads and constraints under different working conditions. Then the strength analyses for each working condition are carried on. The results show that the maximum stresses of three conditions are not beyond the yield limit of material. So front-axle beam can meet strength requirement.(2) Fatigue analysis of front-axle. First, the S-N curve is established. Then, the first principal stress is selected as stress component for analysis of front-axle beam, and the Gerber mean stress correction method is used to modify it. The median fatigue life of front-axle beam is under 800000 times stipulated in the relevant standards. And the results are compared with the test results to further verify the reliability of the finite element results.(3) According to the structure and the stress distribution of front axle, the structure is improved. The fatigue life of the improved front beam meets the standard requirements. The stress of various conditions has also been reduced. Then the first 6 order modal inherent frequency and vibration models of the optimized model are got by modal analysis. The results show that the axle can not occur resonance because of the excitation of road.So the structure improvement is rational.(4) On the basis of the strength and fatigue analysis, the influences of crack’s various parameters on the fatigue life of front axle are studied. According to the stress results, the danger zone of the front axle is defined. The elliptical surface crack unit is established by parametric modeling in the danger zone. And then the parameters such as length, depth of the crack unit are adjusted. The fatigue analysis is carried out again. The fatigue lives are added up. The trend of the fatigue life with the change of the direction of crack, crack depth and length is analyzed. The influence of various crack factors for fatigue life is summarized. The front beam with many cracks is studied in simple. The influence of the distance between the two cracks on the fatigue life is analyzed.The studies not only obtained strength and fatigue life of front axle, but also get the effect of damage crack on fatigue life of front axle. These provide some certain theoretical basis for the design and production for this type of front axle. These researches play a guiding role for predicting its fatigue failure and fracture prevention and provide a valuable method for fatigue analysis of other structure containing cracks. |
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