Coupled Problems

A purely mechanical characterization of parts and specimens is often not sufficient in present engineering tasks. The response of particular materials and combinations of materials to a given mechanical load can for example be influenced by electrical, magnetical or thermal stimuli. Similarly, a deformation of the specimen possibly entails a change in the aforementioned fields. From a continuum mechanical point of view, such coupling phenomena are described by extending the set of equations which describe the purely mechanical interactions. In order to describe the behavior of magnetoactive or thermo-viscoelastic materials which are examined at the chair for computational and experimental mechanics, Maxwells equations and the energy balance have to be taken into account, explicitly. Moreover, appropriate constitutive relations have to be identified.

Magnetorheological Elastomers

Magnetorheological elastomers (MREs) are a special class of materials which typically consist of micron-sized magnetizable particles that are embedded into a non-magnetizable, elastomer matrix. If a magnetic field is applied, mutual interactions between the individual particles result in a change of the macroscopic material behavior which makes MREs attractive to a variety of applications in the field of sensors and actuators. The field-induced deformation of MREs for example allows for their application as valves. If this deformation is prevented, the resulting change in stiffnes can be used to realize tunable vibration absorbers. In order to describe the behavior of these materials within a continuum mechanical framework, finite deformations have to be taken into account. Additionally, MREs show hysteresis effects if they contain particles with a remanent magnetization. Such dissipative processes have to be described with an appropriate phenomenological model.

Thermo-viscoelastic Materials

Due to the inelastic behavior of polymers, their deformation is often accompanied by a dissipation of mechanical energy which results in a change of the temperature. Such a thermomechanical coupling has recently been observed for synthetics which have been analyzed at TU Dresden. Measurements with a high-speed infrared camera have shown that a local, highly dynamical heating occurs if the yield strenght of the material is reached. These results are different from everything that is reported in the literature. For different velocities and polymer materials, an interaction between the mechanical and thermal fields has been proven. A continuum description of this behavior requires models that account for the strong thermomechanical coupling and the complex constitutive behavior of the material. In order to investigate the initial heating of the polymer, a thermo-viscoelastic model has been implemented.