The mechanical behavior of poly(methyl methacrylate) under pressure

Tensile deformation of poly(methyl methacrylate) carried out under hydrostatic pressures up to 4 kbar has shown that the pressure‐transmitting fluid (silicone oil) strongly affects the mechanical properties of this polymer. Unsealed specimens fractured in a brittle manner at almost the same strain of 5% in the whole pressure range examined, while specimens sealed with Teflon tape and rubber showed a brittle to ductile transition at only 0.25 kbar. At this pressure, the craze initiation and shear band initiation stresses were found to become equal. The pressure dependence of the shear band initiation stress could be expressed well with a “nonlinear” pressure‐dependent von Mises criterion and the onset of the shear banding was proved to relate to the enthalpy energy density stored in the specimen. The combination of the nonlinear pressure‐dependent von Mises criterion and the enthaply energy density concept enabled us to predict the pressure dependence of Young's modulus.