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Abstract The yielding behavior of isotactic polypropylene (iPP) sheets prepared by hot pressing was studied by tensile testing. The corresponding microstructural changes in the specimens after testing were investigated by image analysis, optical microscopy (OM), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). The yielding of iPP was found to follow a two‐process Eyring yielding model. In the necked regions, stress‐whitening occurred only in specimens tested over a certain range of strain rates and temperatures. The occurrence of the stress‐whitening was correlated well with the activation of Process II in the two‐process Eyring model. SEM revealed that the stress‐whitening in the necked regions was associated with the formation of craze‐like structures that were parallel to the loading direction. Furthermore, DSC analysis showed that the necked regions of the unwhitened tensile specimens had an additional low‐temperature melting peak. However, no additional melting peaks were found in the stress‐whitened specimens. © 1994 John Wiley & Sons, Inc.
Liu et al. (Thu,) studied this question.