Strains in an inflated rubber sheet

A technique to measure the strain distribution of an inflated membrane is described, and applied to natural rubber inflated to pole biaxial strains of 12%, 26%, and 33%. The radial strain was found to be nearly constant over the entire surface, while the circumferential strain falls to zero at the edge. Thus, biaxial deformation is limited to a narrow region in the vicinity of the pole. These results are quite different from (the very limited) data published previously. The stress-strain behavior was also measured in uniaxial tension, and the strain distribution of the inflated membrane calculated using finite elements. The experiment results and the modeling were in good agreement.