ABSTRACT
There are many different approaches to evaluate the lifetime of rubber parts. What they all have in common is the fact, that the prediction is based on data which results from equidirectional experiments. In those cases a lifetime prediction can lead only to satisfactory results, when it is made for an isotropic and elastic material or for a loadcase with constant loading directions. Under those conditions the equidirectional experiments provide sufficient information for the prognosis of the lifetime. Typical rubber products usually are not loaded equidirectionally and the material itself is inelastic. Therefore, not taking the change of the loading direction into account, the common lifetime predictions are not complete. In this paper a new experimental approach is presented, which allows a split of the lifetime analysis into experiments which are based on tests with varying amplitudes and constant loading directions on the one side and tests with a constant amplitude and rotating loading directions on the other side. A common known example for changing loading directions throughout a deformation is the simple shear process, which is outlined in Figure 1. As can be observed, the directions of the connecting lines between the edges of the square change throughout the simple
shear process. The lines in the undeformed square can be regarded as a representation for the directions of the lagrangian eigenvectors. When the inscribed square reaches a configuration where it is rectangular again, its edges represent the directions of the eulerian eigenvectors. As simple shear is often a dominant deformation in complex deformed structures, the influence of changing loading directions on the lifetime of rubber parts must be taken into consideration.
