Observation of yield in triaxial deformation of glassy polymers

Yield in amorphous glassy polymers has been studied in shear and uniaxial tension/compression, where the volume change is relatively small and the deviatoric components of the strain/stress tensor are dominate. In order to study volumetrically driven yield in a different geometry, a specially designed experimental set-up was developed to create a longitudinal deformation that is dilatationally dominated. The longitudinal stress response of an epoxy resin was measured at temperatures just below Tg, where for the first time yield of a glassy polymer is observed in a nearly triaxial extension deformation. The yield behavior in uniaxial tension and compression was also determined, where all the yield data can be described with pressure-modified von Mises yield criterion but now for much wider pressure range than has been previously accessible.