Polymer Physics (lecture on the limitation of Eyring idea of activation)

Eyring's idea of stress-induced activation has played a powerful role in our description and understanding of yielding in solid materials. According to the idea, all solids would yield, i.e., there are no brittle materials. What's missing here? This lecture explains as part of Polymer Physics lecture series devoted to a unified view of mechanical characteristics of polymeric materials, especially plastics, why polymeric glasses such as PET can be ductile and why they turn brittle at low enough temperatures. For detailed analysis, see our JCP2014: https://aip.scitation.org/doi/pdf/10.... and Polymer2020: https://www.sciencedirect.com/science... Note that this discussion on Eyring activations pertains to all materials including metallic glasses. Surely, metallic glasses are governed by different microscopic physics than the polymer physics discussed here. Surely, the concept of chain network acting as the deliverer of the molecular force to lower the barrier height (within the language of Eyring) does not apply to metallic glasses, and therefore the yielding of metallic glasses cannot be used to reject the key role of chain network in plastics. On the other hand, for glassy materials such as metallic glasses to yield, one may have to identify a structural enabler equivalent to chain network in plastics (arising from chain uncrossability)