Multiaxial yield behaviour of polypropylene

¹ Borealis Polyolefine GmbH, St. Peter Str. 25, 4021 Linz, Austria
² Polymer Competence Center Leoben GmbH, Roseggerstr. 12, 8700 Leoben, Austria
³ Institute of Polymer Materials, Altenberger Str 69, Johannes Kepler University Linz, Austria
⁴ Center for Mechanics of Materials, Solids and Structures, The University of Texas at Austin, 1 University Station, TX 78712, USA
⁵ Institute of Polymer Product Engineering, Altenberger Str 69, Johannes Kepler University Linz, Austria

^a e-mail : michael.jerabek@borealisgroup.com

Abstract

In order to characterize the yield behavior of polypropylene as a function of pressure and to verify the applicability of the Drucker-Prager yield function, various tests were conducted to cover a wide range of stress states from uniaxial tension and compression to multiaxial tension and confined compression. Tests were performed below and above the glass transition temperature, to study the combined effect of pressure and temperature. The pressure sensitivity coefficient as an intrinsic material parameter was determined as a function of temperature. Increasing pressure sensitivity values were found with increasing temperature, which can be related to the change in the free volume and thus, to the enhanced molecular mobility. A best-fit Drucker-Prager yield function was applied to the experimental yield stresses and an average error between the predictions and the measurements of 7 % was obtained.