A Study On The Methods For Measuring And Predicting Fatigue Life Of Rubber Mounts Of Vehicle Powertrain

Rubber mounts are widely used in vehicles to control the motion of the powertrain, todepress the vibration of the powertrain under road excitation and to isolate the enginevibration transmitted to car body or subframe. The rubber mounts are usually subjected tolarge static and time-varying strains in service and often fail due to the nucleation and growthof defects or cracks. It is thus one of the important tasks in designing rubber isolators toprevent fatigue failure, and to assure the safety and reliability of rubber isolators duringoperation. To evaluate the durability of a rubber isolator in its design stage, a study on themethods for measuring and predicting fatigue life of rubber mounts of vehicle powertrain ispresented in this paper.Firstly, the experimental methods for fatigue life measurement of a rubber mount and adumbbell cylindrical specimen are presented. The loading conditons, experimentalenviorenment and test procedure are described in this paper.Secondly, definitions of different damage parameters used for fatigue life prediction ofrubber components are given. The damage parameters discussed in this paper include the peakand amplitude of maximum principal engineering strain, the peak and amplitude of maximumprincipal logarithmic strain, the peak and amplitude of maximum principal Green-Lagrangestrain, the peak and amplitude of octahedral shear strain, the peak and amplitude of strainenergy density, the peak and amplitude of Luo stress, Saintier stress. Finite element analysisis performed to calculate the values of the damage parameters of both the rubber mount andthe dumbbell cylindrical specimen under external fatigue loadings.Thirdly, thirteen fatigue life prediction models using the damage parameters mentionedbefore are established based on the experimental results of dumbbell cylindrical specimens,which have the same rubber compounds as those of the studied rubber mount. The fatigue lifeof the mount is then predicted using the thirteen previous models and compared with themeasured fatigue life of the rubber mount. It is shown that the model using Luo stress,including peak and amplitude value of Luo stress, and Saintier stress as the damage parameter can predict the fatigue life within a factor of two of the measured life, whereas the predictedfatigue lives from other models using the other damage parameters fall in a factor of four ofthe measured life. Considering the sum of the squares of the relative prediction error (SSRPE),the SSRPE of the amplitude of Luo stress or Saintier stress is the smallest of the thirteendamage parameters.It is concluded that the proposed model for fatigue life prediction with the amplitude ofLuo stress or Saintier stress as the damage parameter is more appropriate to estimate thefatigue life for the type of rubber mount.