On thermo-viscoelastic experimental characterization and numerical modelling of VHB polymer

Abstract

Recently, the so-called Very High Bond (VHB in short) tape has proven to be an ideal polymer for producing devices made of electric field-responsive functional materials, e.g., actuators in soft robotics, stretch sensors in wearable devices, and energy harvesters generating power from ambient motions. The VHB polymer is commercially available in several thicknesses. For this study, we have selected VHB 4905 due to its wide use as a common material for dielectric elastomers. The acrylic-based polymer is highly deformable, extremely viscoelastic, and highly sensitive to temperature fluctuations. Hence, in order to understand its mechanical and electro-mechanical behaviour, extensive experiments need to be conducted to unravel temperature dependencies in addition to strain-rate dependences. In this study, we present a wide variety of temperature experiments ranging from -30°C to 80°C at various strain rates and stretch levels under homogeneous deformation and temperature fields. The study demonstrates a pronounced influence of the temperature on the mechanical response of the VHB polymer. For VHB within the temperature range of our study, an increased temperature mechanically softens the material and vice-versa. After conducting a wide range of experiments, we propose a finite strain thermo-viscoelastic constitutive model that is an extension of a phenomenologically-motivated model where a non-linear evolution law is devised based on the classical concept of the multiplicative decomposition of the deformation gradient. Then, decoupled one-dimensional equations are derived and fitted to experimental data to identify relevant material parameters appearing in the model. The thermo-viscoelastic model validation shows its reasonably good capability to predict the experimental results.