کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
5178055 | 1502488 | 2017 | 9 صفحه PDF | دانلود رایگان |
- Accurate WAXS measurement of crystal strain in the low strain domain.
- Determination of strain onset for local crystal yielding.
- Computing critical crystal stress at onset of crystal yielding.
- Evidence of variable stress transfer between lamellae depending on crystallinity.
The influence of microstructure and temperature on the initiation of yield stress and strain of high-density polyethylene are examined using a set of linear and branched polyethylenes. The polymers were crystallized in different ways in order to get samples covering the range of crystallinity 0.5 ⤠Xc â¤Â 0.8 and crystallite thickness 8 nm â¤Â Lc â¤Â 29 nm. In contrast to the conventional macroscopic yield strain and stress, the initiation strain εyi and stress Ïyi were estimated from the macroscopic stress-strain curves at the onset of local plasticity as judged from in situ WAXS experiments upon tensile deformation. Phenomenological linear relation was observed between Ïyi crystallinity at each draw temperature Td. The dislocation model was applied to check the correlation between Ïyi and crystal thickness. In order to also account for the chain topology, namely the concentration of stress transmitters ST, a modified Eyring's approach was proposed. This modelling provides a good prediction the Ïyi dependence on Lc and ST in the context of thermally activated rate processes. Finally, anelastic stress gauge, Ïccr, was determined from local strain measurements in crystals at the same local strain as for Ïyi. This critical elastic stress at initiation of crystal plasticity displayed a good correlation with Ïyi at high crystallinity. However, Ïccr was found to deviate from Ïyi with increasing Td particularly at low Xc values. This finding was attributed to the activation of the crystalline mechanical relation that involves a significant drop of Ïyi with increasing Td in the crystalline lamellae under shear yielding whereas it does not affect the theoretical Ïccr elastic stress.
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Journal: Polymer - Volume 118, 2 June 2017, Pages 192-200