The Effect of Pressure on the Ultimate Properties of Elastomers

Abstract

Abstract Many studies have been made on the effect of pressure on the mechanical properties of elastomers, but these studies have invariably been limited to small-strain behavior because of equipment limitations. This small-strain limitation has now been removed with the construction of a novel high-pressure chamber which allows large tensile deformations to be applied to samples at pressure up to 300 MPa and temperatures from 0°C to 200°C. The effect of pressure on the ultimate tensile properties of nitrile, butyl, EPDM, Viton®, silicone, and polyisoprene elastomers has been determined. The tensile strengths and moduli all increase with pressure, but not in a monotonic fashion. In several cases, the tensile strengths increase rapidly with increase in pressure up to about 60 MPa, but then they remain almost constant with further increases in pressure. The ultimate extensions show a more complex behavior. Although the ultimate extensions typically increase with pressure, several samples, e.g., nitrile, EPDM, butyl and Viton, show maxima in ultimate extensions vs. pressure. Other than butyl, these samples also show yielding behavior at large extensions. This is attributed to glass-transition effects for nitrile and Viton, and to pressure-induced crystallization effects for EPDM.