| Suspension system isthe key part ofchassis.The random dynamic load of road is one of the most influential factors which affect the fatigue life of suspension system when the vehicles running.It is high cost and long time to determine and evaluate the fatigue life of the suspension system by road testing method.So the fatigue reliability research and analysis of the SUVrear suspension are accomplished in this thesis.Those analyses are based on the finite element theory.Taking the multi-link rear suspension of the SUV as the research object and fatigue life analysis of the lower control arm were completed in this paper.Mainlywork of the following aspects was implemented.Firstly,the multi-body dynamics model of the multi-link suspension was built and simulated in Adams/Car according to the hard points coordinates of each part.The simulation results show that the relative error of suspension stiffness is 4% by comparing the suspension stiffness simulation results with the K&C test results.The error margin meets the project requirements and the suspension model is valid.Secondly,the SUV multi-body dynamics model was established in Adams/Car.Then the tire-road contact force in static load condition,acceleration start condition and turning condition were calculated respectively.According to the mathematical model of random road,theG-class random road conditions weresimulated in Simulink.The G-class road excitation was imported in Adams/Car andthe tire-road contact force in G-class random excitation condition was analyzed.The comparison results showed that the tire-road contact force reached the maximum under this condition.Thirdly,the lower control arm'sforce under the G-class random excitation condition was chosenas load boundary conditions in its finite element analysis.The finite element analysisin HyperWorks can obtain the contour chartsof stress,the displacement variation image,and the natural frequency of each rank and their corresponding vibration mode.Theresults show that the maximum stress of the lower control arm is 276.2MPa and the strength can satisfy the requirement.The high stress distributes mainly in the region ofthe boundary where there is stress concentration.The first six order modes are rigid mode and the low modal frequencies(seventh order to twelfth order)are located between 602.3Hz and 2384.8Hz.The road-time frequency in Chinais mainly distributed between 0.33 Hz and 28.3Hz.The frequency of polarization of the suspension system is located between 1Hz and 1.6Hz.Sothe low modal frequencies are much larger than the frequency of the road surface and the polarization of rear suspension system,there will be no resonance phenomenon.The mode shape diagram of the lower control arm shows that the overall structural isstable.Finally,simulation analysis of the vehicle model was finished in Adams/Car.The load spectrum of the lower control arm was obtained combining the rain flow cycle counting method.The fatigue life analysis of the lower control arm was accomplished in HyperWorks/RADIOSS which is based on the finite element analysis results and the Miner linear fatigue cumulative damage theory.The distribution diagrams of fatigue life and fatigue damage were obtained.The resultsshowed that the fatigue life of lower control arm can meet the requirements of project and the simulation analysis results can provide reference for fatigue testing of the suspension.The light-weight of the lower control arm is the goal.The topological optimization method was used to get the topological structure of the lower control arm,the optimize region is determined by the fatigue analysis results.Comparing the fatigue life with the un-optimized,the fatigue life of the lower control arm is greatly improved. |
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