Application of the Virtual Fields Method to Rubbers Under Medium Strain Rate Deformation Using Both Acceleration and Traction Force Data

Abstract

This paper describes an experimental technique for characterizing the uniaxial stress–strain relationship of rubbers under medium strain rate deformation. This method combines the virtual fields method (VFM) and high-speed imaging with digital image correlation. The VFM can be expressed so that force measurement during dynamic loading is no longer required; instead, surface measurements of acceleration, which occurs as a result of wave propagation in the specimen, are used as a ‘virtual load cell’. In a previous paper, the authors have utilized this technique for characterizing material parameters for the dynamic behaviour of rubbers using a drop-weight apparatus. One limitation of this technique is that the stability of the parameter estimation depends on the length of the specimen. When the loading stress wave reaches the fixed end of the specimen, a static equilibrium state is instantaneously achieved. At this instant, the acceleration fields are no longer able to provide information, and the identification is unstable. In order to overcome this limitation, the present paper proposes a VFM based method able to produce stable identification even at this equilibrium instant. This procedure utilizes both inertial and external forces, and a new experiment apparatus has been developed for simultaneously measuring these two sets of data. This new procedure is described using results from simulations; then, the experimental system and results will be presented.