Research Of Road Roughness Vertical Transfer Mechanism And Its Impact On Vehicle Structure Fatigue Damage

Road roughness is one of primary input that caused to damage on the vehicle structure or component, and is a fundamental factor that impact on the vehicle fatigue life. To reveal the transfer mechanism on random road roughness and the vehicle structure damage by it caused, in this paper, each grade road is reconstructed equivalently based on the measured road roughness. Road roughness transfer mechanism is analyzed by established the model of vehicle and pavement coupled. Through fatigue damage theoretical and measured load spectrum, the law of vehicle structure fatigue damage is analysis under the condition of proving ground road, and subframe, control arm and other structures life are predicted.(1) Road roughness equivalent reconstruction based on measured road spectrumElevation data on different level pavement and proving ground is tested by applying road roughness laser test systems that project team developed. The data trend term is extracted by using the empirical mode decomposition, and data is removed the noise by using the of empirical mode decomposition wavelet hard threshold method based on fixed threshold criteria. Power spectral density of typical pavement data is analyzed. Each class of virtual pavement is reconstructed by two-dimensional AR model, and reconstruction results are tested and analyzed by using the F-test and associated index method. A software on pavement virtual reconstruction based on measured elevation data is developed by using the hybrid programming technology on VC++and Matlab, and can generate virtual road files applied to the CarSim, VPG, ADAMS dynamics simulation software. The results show that the reconstruction accuracy are high between reconstruction spectrum and measured spectrum. It provides accurate road excitation for the vehicle road coupling system dynamics simulation and vehicle fatigue durability analysis.(2) Road roughness vertical transfer characteristics simulation and experimentVehicle and road vertical coupling dynamics model is built by three subsystem models including on1/4vehicle models, Euler-Bernoulli road model considered pavement deformation, vertical coupling elastic tire model considered the inclusive features. Some performance parameters are for recognized on a sport utility vehicle suspension and tire. Pavement vertical displacement is resolved by analytical method and simulation analysis, on this basis. Then acceleration and displacement parameters in wheels and body are simulated in the vehicle and road vertical coupling system, and road roughness vertical transfer mechanism is analyzed. Vehicle tests verify the suspension displacement and wheel vertical acceleration parameters characteristics, and dynamic transfer characteristics of complex road roughness are analyzed in wheel-body subsystems. The results show that with increased speed and reduced road grade, dynamic displacement caused by road excitation induced increased gradually, and increasing trend is nonlinear. And complex road roughness couldn’t change the wheel-body system frequency response characteristics, and its stochastic characteristic is consistent with vehicle structural load, and it is the root cause of vehicle structure fatigue damage.(3) Fatigue damage analysis and life prediction of vehicle structure caused by different road roughnessIn order to analyze fatigue damage of vehicle structure under the road roughness, some important structure three dimension models such as front suspension and rear suspension are built. According to the FEA result, and the key points in the structures including front suspension control arm, subframe, rear suspension arm and cross arm are determined, then load test points are determined. According to the project, the load spectrum test in a vehicle test field is finished. By rain flow count method, the load spectrum of all test points is drawn up, its mean values are in line with normal distribution, and amplitude values are in line with Weibull distribution. By ncode8.0glyphworks software, the fatigue damage distribution laws of vehicle structures (subframe and control arm etc.) are analyzed under the strengthened test field road pavement, and the life prediction is done, then the network diagram and equivalent coefficient method indicting vehicle structure fatigue damage are proposed. The results show that vehicle structure fatigue damage increases with road grade decreasing, which can be affected drastically by the conditions such as vehicle acceleration and turning.The innovations lie in:(1) Road equivalent reconstruction method based on the measured spectrum is proposed. During the process of vehicle dynamics simulation, aimed to the using purposes and requirements of the different users, the virtual road pavements equivalent with measured road spectrum are reconstructed, and the road reconstruction software is exploited, which can provide accurate road roughness for fatigue tests of the whole vehicle and parts, make vehicle dynamics simulation be more accurate and reliable.(2) Vehicle-road vertical coupling dynamics model considering tire enveloping property is built, then the vehicle structures response properties for complex road roughness under the action of vehicle-road vertical coupling. It provides a more accurate solving method for vehicle fatigue durability research.(3) Network diagram method of evaluating vehicle structure fatigue damage caused by combination roads and equivalent coefficient method based on damage equivalent are proposed. The method of using central angle indicating damage contribution rate caused by different roads and radius indicating damage density, the forming network diagram envelop area indicting fatigue damage is referred as network diagram method. By the rule of fatigue damage equivalence, the equivalent mileage and factor of any road compared with focused road are calculated, which is the damage equivalent method. It provides important methods for the vehicle road test specification revision, can cut test cost greatly.Taken road roughness as basis, the effect research of vehicle fatigue duration is developed, which provides important basic theory and effective method for the research of vehicle-road coupling dynamics and fatigue duration performance.