Study On Virtual Test Method Based On Real Road Spectrum For Virtual Fatigue Prediction

As the fatigue of automotive structures determine the life of the car, and thefatigue of vehicle are usually predicted by real tests or computer-aided techniques.The test can provide very accurate results, while the test cycle is very long and thecosts are also enormous; the virtual simulation is subject to major differences betweencomputer-assisted technology and the actual test or fatigue theory, and the predictionaccuracy is low with a limited application in engineering. Currently, the automotivestructural fatigue assessment mainly depends on the actual test, which greatly limit sits research, development efficiency and cost.In this paper, computer aided technology for automotive structural fatigueprediction system is investigated. We propose a virtual test method to improve theaccuracy of virtual simulation, and also apply it to the automotive structural fatiguelife prediction, which also improve the accuracy. As this method can predict theautomotive structural fatigue very quickly and accurately, and guide structural fatigueperformance optimization, and then can reduce the number of the virtual test, researchand development period and cost. This new method has very important theoretical andengineering application value. The main contents and innovations include:(1) Proposed virtual test method based on real road spectrum to improve theaccuracy of virtual simulation of automotive. In the virtual simulation of vehicleusing computer-aided techniques, the relationship of road-tires-vehicle coupling isvery complex, especially for tire model simulation, which limiting t he improving ofaccuracy for fatigue prediction. In this paper, virtual test method based on real roadspectrum is proposed, the iterative feedback is used to correct the virtual simulation.This method avoids the use of inaccurate tire model, which improv es the accuracy ofsimulation. The body-in-white and parts virtual test bench are then establishedaccording to the real characteristics of vibration and shock tests.(2) Proposed sub-weighted frequency response function of identifying method toimprove the system’s frequency response function recognition accuracy. Systemfrequency response function recognition is the basis of virtual test method based onreal road spectrum. In the real test of vehicle, non-linear factors should be considered,while the system frequency response function only considered the linear stage, whichinducing large error of virtual simulation. In this paper, sub-weighted frequency response function of identifying method is proposed. In this method, the newfrequency response function is then obtained by sub-weighted of linear and nonlinearpart. Numerical case shows that the method can decreases the system’s initial error,reduce the difficult of reproducing real road spectrum in virtual bench.（3）Proposed an adaptive iterative algorithm of road simulation to solve thedifficulty of convergence for reproduction virtual simulation using the real roadspectrum. At present, The Remote Parameter Control method is adopted in the virtualroad simulation with a simple iterative correction to obtain the nonlinear system,which inducing the iteration process easy divergence and low efficiency. In this paper,adaptive iterative error feedback control is adopted in the virtual test method based onreal road spectrum, the error feedback will be obtained in each subsequent iteration,which can solve the convergence problems quickly and accurately and reproduce thespectrum of virtual simulation with high computational efficiency.(4) Proposed virtual test method for vehicle parts based on real road spectrum toget the accuracy prediction of fatigue. In the actual driving test, parts are installed inthe car, and exposed to complex spatial impact load, and we cannot get its accuratevalue by direct tests or simulations. To solve this problem, this pa per proposed virtualtest method for vehicle parts based on real road spectrum, and get accurate loadboundary conditions for fatigue prediction, which will guide its structural design anddurability improvement. Numerical method and experiment verified th at it caneffectively shorten the development cycle for automotive parts development andimprove engineering efficiency, realize rapid promotion of durability for automotiveparts.(5) Proposed virtual test method for vehicle body-in-white based on real roadspectrum to get the accuracy prediction of fatigue, and Recovery Based StressSub-model Method using stress recovery is also proposed to reduce the computationsimulation and optimization time, which leads to a substantial increase in efficiency.In the actual vehicle test, the vehicle body structure exposed to the impact load fromthe tire, and suspension, and due to the complexity of the suspension and tire model,the conventional methods cannot get exact impact load for the body structure, thus thefatigue life prediction accuracy is very low. This paper proposed virtual test methodfor vehicle body-in-white based on real road spectrum, which improve vehicle virtualfatigue simulation accuracy and computational efficiency. The accurate bodystructure fatigue prediction can also guide its structural durability optimization.Numerical simulation and experiment verified that it can reproduce the shock and vibration on the road test, realize rapid promotion of durability for vehicle body,which effectively guide the design and optimization of the body structure.