Applications of the virtual fields method to the mechanical behaviour of rubbers under dynamic loading

Experimental techniques for measuring the mechanical response of rubbers under dynamic loading are developed utilising the virtual fields method (VFM), to inversely identify constitutive behaviour from experimental observations. Rubbers and other âsoftâ materials are difficult to characterize using traditional dynamic techniques such as the split Hopkinson bar: the low sound speed makes it difficult to achieve static equilibrium and the small supported forces give low signal-to-noise ratios in the experimental data. In this research, the dynamic VFM with the aid of high-speed imaging is applied to dynamic tensile experiments to resolve these difficulties. The VFM is a mathematical technique that makes use of the principle of virtual work. Manipulation of this equation enables us to remove the need for traditional force measurement, instead exploiting acceleration full-field data as a virtual load cell. Thus, the aforementioned difficulties are no longer of concern: the technique requires that the specimen is not in static equilibrium and that inertial forces are significant compared to material forces. Two dynamic tests and dynamic VFMs are developed and applied to tensile drop-weight and gas-gun driven experiments. The first uses small amplitude dynamic deformation superposed on static pre-stretching. Dynamic identifications at a number of pre-strains are collated to identify the complete nonlinear behaviour. The second utilizes a large strain amplitude of dynamic loading: one experiment characterizes the full response. Further applications of the dynamic VFM are explored in order to improve the first method and to extend the identification capability, and experiments performed at non-ambient temperatures allow a preliminary exploration of time-temperature superposition