Hyperelastic Properties of Flexible Adhesive Systems

For flexible (mbbery) adhesives which show Tg far below room temperature, hyperelastic material models are generally used. In the hyperelastic regime, standard solutions are available which use various types of potential functions [7]. The flexible adhesive systems investigated were best fitted by a potential function which is formulated in terms of the principal stretches Aj originally suggested by Ogden [Eq. (1)] [8]. 

For our adhesive systems, a first-order approximation (n=l) was sufficient to achieve a good fit. The material was treated as incompressible. The temperature-dependent parameters n and a were determined by fitting theoretical nominal stress-strain relationships following from Eq. (1) to the experimental data. The nominal stress-strain relationships are calculated by differentiating Eq. (1) with respect to the principal stretches. For simple deformation modes, e.g., uniaxial tension, uniaxial compression, and simple shear, the principal stretches and their relationships are easily obtained by geometrical considerations. For a reliable determination of the values of fi and a, these calculated stress-strain relationships were fitted to experimental data which were measured in the corre- 

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