A High Precision Experimental Method to Determine Poisson’s Ratios of Encapsulant Gels

A high precision technique for measuring Poisson’s ratios of elastomers was experimentally implemented. Test fixtures consisted of hollow metal cylinders fitted with matching pairs of pressure sensors at the top and bottom. Evaluation of a preliminary low-pressure fixture led to the development and testing of a high pressure version to investigate potential nonlinearities in the response. A series of elastomeric gels was evaluated by casting them into the cylinders and pressurizing the free end. The pressure at the closed end of the gel was attenuated by the resulting deformation in the gel. The resulting pressure profile obeys equations similar to classical shear lag behavior. Poisson’s ratio was easily calculated from the ratio of the two pressures and the aspect ratio of the gel specimen. A series of seven encapsulant gels was characterized. Consistent results for most gels were obtained to the fifth significant digit, confirming the high precision capabilities of this simple technique. Accurate information on Poisson’s ratio may be required for elastomeric materials that are used in constrained configurations where volumetric changes can be important.