Computation of material forces for the thermo-mechanical response of dynamically loaded elastomers

Elastomers are widely used in today's life. The material is characterized by large deformability upon failure, elastic and time dependent as well as non-time dependent effects which can be also a function of temperature. In addition, cyclically loaded components show heat build-up which is due to dissipation. As a result, the temperature evolution of an elastomeric component can strongly influence the material properties and durability characteristics. Representing best the real thermo-mechanical behaviour of an elastomeric component in its design process is one motivation for the use of sophisticated, coupled material approaches within numerical simulations. In order to assess the durability characteristics, for example regarding crack propagation, material forces (configurational forces) are one possible approach to be applied. In the present contribution, the implementation of material forces for a thermo-mechanically coupled material model including a continuum mechanical damage (CMD) approach is demonstrated in the context of the Finite Element Method (FEM). Special emphasis is given to material forces resulting from internal variables (viscosity and damage variables), temperature field evolution and dynamic loading. Using the example of an elastomeric component, for which the material model parameters have been previously identified by a uniaxial extension test, material forces are evaluated quantitatively. The influence of each contribution (internal variables, temperature field and dynamics) is illustrated and compared to the overall material force response. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)