Finite Element Procedures in Modelling the Dynamic Properties of Rubber
Sammanfattning: Rubber is not only a non-linear elastic material, it is also dependent on strain rate, temperature and strain amplitude. The non-linear elastic property and the strain amplitude dependence give a non-linear dynamic behavior that is covered by the models suggested in this thesis. The focus is on a finite element procedure for modelling these dynamic properties of rubber in a way that is easy to adopt by the engineering community. The thesis consists of a summary and five appended papers. The first paper presents a method to model the rate and amplitude dependent behavior of rubber components subjected to dynamic loading. Using a standard finite element code, it is shown how a model can be obtained through an overlay of viscoelastic and elastoplastic finite element models. The model presented in the first paper contains a large number of material parameters that have to be identified. The second paper suggests a method to identify the material parameters of this model in a structured way. Experimental data for thirteen different materials were obtained from harmonic shear tests. Using a minimization approach it is shown how the viscoelastic-elastoplastic model can be fitted to the experimental data. Using the methods presented in the first two papers, a radially loaded rubber bushing was modelled in the third paper. The material properties of the finite element model were based on dynamic shear tests. The dynamic response of the finite element model of the bushing was then compared to measurements of a real bushing. Thus, verifying the entire procedure from material test to finite element model. Steady state loading is a very common load case for many rubber components. Although it is possible to analyze this load with the earlier discussed viscoplastic model, the regularity of this load lends it self to described in a more efficient way. For this load case a simplified viscoelastic method is adopted. The basic idea of this model is to create a new viscoelastic model for each amplitude. In paper IV this method is compared to the previous viscoplastic model as well as verifying measurements. In paper V both the viscoelastoplastic model and the modified viscoelastic model are used to analyze rubber coated rollers. Different aspects of the two models are highlighted and the models are used to analyze how the non-linear dynamic characteristics of the rubber material influences the rolling contact. Together the five papers present a set of tools for analyzing the dynamic behavior of rubber components, from material testing to finite element modelling.
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