Experimental Thermomechanical Analysis of Elastomers Under Uni- and Biaxial Tensile Stress State

The objective of the present work is to demonstrate an experimental methodology to determine the viscoelastic material behavior of elastomers independent of the mechanical loading conditions. For this purpose two model materials (elastic and damper formulation) were investigated. The experimental effort ranged from classical uniaxial dynamic thermomechanical analysis (DTMA) and monotonic loading to monotonic biaxial testing. The performed monotonic experiments were loading rate and temperature dependent. Before applying the experimental methodology, some fundamental presumptions had to be verified. First, the applicability of the well-known time-temperature superposition principle to the elastomers, and second the separation of thermomechanical loadings, in which the temperature effects on the mechanical behavior of the materials could be characterized by an appropriate shift factor function; if this function is fundamental, then it should be independent of the mechanical loading condition. The shift factor functions were determined for the investigated elastomers from the DTMA results and were applied for the monotonic uni- and biaxial loading. Two biaxial tests (bulge test and planar biaxial tension test) were performed to show a direct calculation method for the stresses from planar biaxial tests by utilizing FEA with a material model, whose parameters were defined by the bulge test results.