The nature of strain hardening in glassy polymers is investigated by studying the mechan-ical response of oriented polycarbonate in uniaxial extension and compression. The yieldstress in extension is observed to increase strongly with pre-deformation, whereas it slightlydecreases in compression (the so-called Bauschinger e®ect). Moreover, oriented specimenstend to display increased strain hardening in extension, whereas this nearly vanishes incompression. It is shown that these observations can be captured by the introduction of aviscous contribution to strain hardening in terms of a deformation dependence of the flowstress. This can originate either from a deformation-induced change in activation volume,as observed for isotactic polypropylene, or from a deformation-induced change of the rate constant, as observed for polycarbonate, which causes the room temperature yield kineticsof this material to shift from the alpha into the (alpha + beta) regime.
|Number of pages||12|
|Journal||Journal of Polymer Science, Part B: Polymer Physics|
|Publication status||Published - 2010|