The Analysis Of Modal Characteristics And Its Influencing Factors For Brake Disc

Brake disc is the major component of braking system, the performance of brake disc will influence automobile travel security directly. When vehicle brakes, if excitation frequency is close to the natural frequency of brake disc, resonance will be caused. It would result in loud noise and serve vibration, and affect the comfort. So it is essential to analyze the modal characteristic of brake disc and its influence factors, and further to study the dynamic characteristics. If the mutual influence between brake disc and brake system can be predicted and resonance can be avoid by structural optimization design, the safety, reliability, comfort can be improved when vehicle braking. High-precision finite element(FE) model is the foundation of structural dynamics analysis and optimization design. In order to obtain accurate FE model of brake disc, initial FE model can be update by experimental modal analysis results, and the correlation between finite element modal parameters and test modal parameters will be carried out. The accurate FE model also is the foundation for analyzing the impact of geometry and material parameters on modal characteristics.First of all, the FE model of brake disc was build using APDL Language of finite element analysis(FEA) software, and undamped natural frequencies and mode shapes can be obtained by FEA. Then experimental modal analysis(EMA) was conducted,and the modal parameters of brake disc were accurately extracted by Least Square Complex Exponential method(LSCE) and Least Complex Frequency method(LSCF) combining the stabilization diagram with the complex modal indicator function. Further, the correlation analysis between finite element modal parameters and experimental modal parameters were calculated. For the problem that there exist obvious frequency deviations between FEA and EMA, parameter updating method based on sensitivity analysis was applied in this paper, which transform the finite element model updating into the optimization problem of minimizing frequency deviation between FE model results and vibration test data. The maximum frequency deviation of modes 1-9 was reduced from-9.23% to-2.19% by updating Young’s modulus, density and Poisson’s ratio, and the Cross MAC values between corrected FE mode shapes and experimental mode shapes are near to 1, this indicated that the corrected FE model with high precision.On the basis of the accurate FE model of brake disc was obtained, the effect of changing geometry sizes and material parameters on modal characteristic of brake disc was analyzed. The research indicates that radial total size, radial size of inner disc, axial total size of hollow double plate body, the distribution density and sizes of spokes in brake disc, Young’s modulus and density are mainly influence factors to natural frequencies of modes 1-9 of brake disc. The modal characteristic of brake disc can be improved by changing the mainly influence factors to natural frequencies, this point the way for the optimization design of brake disc and the controlling of braking noise.It’s worth mentioning that when the correlation of mode shapes was analyzing, in order to eliminate the angle errors of repeat mode shapes between FEM and EMA for brake disc and then realize accurately quantitative modal correlation analysis, the generated mechanism for angle errors of repeat mode shapes of different modal model was revealed and a new modal shape correlation correction method of repeated mode of cyclic symmetric structure was presented. Firstly, the initial Cross MAC value of each double modes between FE mode shapes and experimental mode shapes was calculated. Secondly, angle errors and the corresponding point number which should be rotated were worked out. Finally, the corrected Cross MAC value and accurate analysis results of modal correlation for brake disc were achieved after the finite element modal shapes was matched again. The method not only can be used to correct the correlation of double mode shapes of cyclic symmetric structures, but also the correction efficiency compared to exist cyclic group and elementary rotation transformation methods was increased.