Fatigue Life Evaluation Of Rubber Material Based On Crack Energy Density And Dynamical Mechanical Analysis

The fatigue damage is the one of the key factors that restricts the service life ofrubber products under the cyclic loading. But there are no united theories to predict thefatigue life of rubber because of the complex relationship between strain and stressresulting in the large deformation, addition to the shape of structure, the effects ofenvironment and so on. Crack nucleation and crack growth is the most commonly usedmethod to predict the fatigue damage process. Crack nucleation method is focusing on thenucleation life, and the Crack growth method is used to simulate the crack initiationprocess. But for most of rubber, the crack nucleation life accounts for more than80%ofrubber’s total service life. Taking strain history of the finite element analysis results as aninput, combining the crack propagation experiments with the S-N curve of uniaxialtensile experiment, based on the CED theory, this paper is intended to predict thenucleation fatigue life of rubber structure under the multi-axial loading.The main research work and conclusion are listed as follows：1. Classical methods for predicting the multi-axial nucleation fatigue life of rubberare sketched and the data fitting ability of different fatigue models are analyzed andcompared in this paper. Results show that the equivalent strain fatigue model has a goodability to fit the multi-axial fatigue data when the main damage comes from the tensilecrack by taking no consideration into shortcomings in this model. Compared with themaximum principle strain fatigue model, energy density fatigue model has the betterfitting ability when the rubber is under the shear loading. The model in critical planemethod, containing the effect of shear force, would have an obvious advantage to fit themulti-axial fatigue data.2. Based on CED (Crack Energy Density) theory, a new numerical-experimentalanalysis approach is proposed to evaluate the fatigue life of rubber structure under thecyclic multi-axial loading. By using the proposed method, the fatigue life and thecracking orientation can be predicted accurately. One advantage of the proposed methodis that the time and cost of characterizing the rubber fatigue property can be saveddramatically. As an example, the method is applied to analyze and optimize an air springshear pad. It can be found that the simulated results agree well with the experiment data.Base the method, also, the Haigh diagram that mapped the effects of ample strain andmean strain to the unaxial fatigue life of rubber have been given. 3.Taking the maximum principal strain and strain energy density as damageparameters, the multi-axial fatigue life of rubber bearing are predicted and comparedRespectively. The results show that the strain energy density fatigue model tend to beconservative when predicting the fatigue life, and the maximum principal strain fatiguemodel is more sensitive to the strain history of rubber structure.