A well-defined yield point appears during the
tensile deformation of pure ST2. After the yield point,
the stress falls rapidly (strain softening), reaches a
minimum and again rises slowly (strain hardening).
This sample breaks at a strain and stress of 257% and
20 MPa, respectively. Macroscopically, the deformation
occurs via necking and drawing of the tensile
specimen. The yield point is visible in ST2/PS082
blends as well. However, they show only strain
softening. With increasing PS082, the extent of neckelongation
(drawing of the tensile bar) decreases and
the tendency for brittle fracture increases. The blends
exhibit macroscopic stress whitening that indicates
the formation of local deformation zones, such as
crazes. The stress whitening becomes pronounced
until a PS082 content of 40 wt%, and it becomes
less distinct with increasing PS082 content due to
extreme localization of the deformation zones (see
Section 5.4).