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A unified framework to understand ductility in glassy polymers : from crazing, brittle-to-ductile transition to rubber-toughened polymers
Shi-Qing Wang
Faculty of Department of Polymer Science, University of Akron, Akron, OH
Abstract
In my lab, we focus on building a molecular-level understanding of polymer mechanics in both liquid and solid states. This is a journey that involves three episodes or steps : a. Phenomenology and conceptual foundation of polymer melt rheology, b. Molecular mechanics of polymer glasses, c. Brittleness and ductility of semicrystalline polymers. The latter two subjects can only be understood after the molecular foundation [1] for polymer melt rheology has been established. In this talk, I will concentrate on subject b, exploring how we can understand the remarkable ductility of glassy polymers. In a pedagogical way, I will explain why a valid theory to explain yielding of glassy polymers must address when the polymers fail to remain ductile, i.e., unable to yield and undergo brittle fracture. The universally applied Eyring idea of activation alone is powerless to provide the foundation for the molecular mechanics of glassy polymers. Rich experiences with melt rheology have provided us the crucial ingredients to formulate the basis [2] for all aspects of mechanical behavior of polymeric glasses including brittle-ductile transition, crazing and rubber-toughening.
References
[1] Nonlinear polymer rheology : macroscopic phenomenology and molecular foundation, S. Q. Wang, Wiley (2018)
[2] A phenomenological molecular model for brittle-ductile transition and yielding of polymer glasses, S. Q. Wang et al., J. Chem. Phys. 141, 094905 (2014).