Investigating nature of stresses in extension and compression of glassy polymers via stress relaxation. (12th August 2020) - Liu, Jianning
Abstract: Our experiments show for both uniaxial extension and compression that the post-yield stress relaxation can be slower than the pre-yield stress relaxation on all time scales. Such phenomena reveal that high stresses may result from chain tension due to large deformation of the chain networking in glassy polymers. In combination with molecular dynamics (MD) simulation, we demonstrate that even in the case of compression the stress buildup stems from the mechanical resistance against the lateral expansion of the chain network, which produces bond distortion such as bond stretching. As further evidence of how chain network dictates the mechanical responses, it is shown that significant network deformation produced by large deformation can suppress segmental relaxation in compression. Thus, the present study has made a first combination of experiment and MD simulation to elucidate (a) the remarkable effects that the chain network has in response to large post-yield deformation and (b) the direct (indirect) chain-network contributions to the macroscopic stress in extension (compression). Graphical abstract: Image 1 Highlights: Stress relaxation after post-yield deformation can be slower than preyield stress relaxation. Chain network resists lateral extension, resulting in buildup of high compressive stress. Post-yield stress relaxation is nearly temperature independent. Sufficiently large compression suppresses segmental relaxation.