Theoretical and Experimental Investigations of the Plane Strain Compression of Amorphous Polymers in the form of a Flat Plate

Abstract

This paper studies a test method which overcomes some of the disadvantages of the tensile test. It is based on the plane-strain compression test, initially developed by Green, and is suitable for large strains. The experimental investigation of plane-strain compression test is carried out on Polymethylmethacrylate (PMMA) in the form of a flat plate, over a wide range of experimental conditions which cannot be reached in tensile tests owing to the brittle nature of the material. Over the whole range investigated, load-compression curves exhibit a well-defined maximum followed by a part where the load is minimum. The maximum is taken as the yield point and the minimum corresponds to the stationary plastic flow mode. The Stress analysis is made on the basis of plasticity theory, taking into account the influences of geometry and friction at the interfaces dies-sample. The equivalent yield stress is shown equal to the one obtained with other stress systems (uniaxial compression, uniaxial extension, simple shear). The plot of the stationary value of equivalent plastic flow stress normalized to the shear modulus versus the temperature normalized to Tg, formally illustrates the existence of two deformation regimes. After plane-Strain compression test, the grid dug by scanning electron microscope into the sample on the surface normal to the longitudinal axis of the dies allows visualization of the deformation state under optical microscope.