Velocity criterion for rate-dependent deformation and failure mechanisms in glassy polymers under quasi-isentropic uniaxial strain tension

T Liu and MH Zhu and QM Li and LM Chen, POLYMER, 336, 128896 (2025).

DOI: 10.1016/j.polymer.2025.128896

Glassy polymers, owing to their sophisticated molecular structures and chain aggregation states, can undergo multiple micromechanisms in response to increasing strain-rate loading. Employing the quasi- isentropic (QI) technique, we systematically investigate the dynamic tensile behavior and the underlying molecular mechanisms of pyromellitic dianhydride (PMDA)/4,4 '-oxidianiline (ODA) polyimide (PI) across seven orders of magnitude in strain rate (10(8) to 10(15) s(-1)) through large-scale all-atom molecular dynamics simulations. Our results reveal three distinct strain-rate-dependent regimes in the dynamic tensile response of PI: low (10(8)-10(11) s(-1)), moderate (10(11)-10(14) s(-1)), and high (>10(14) s(-1)) strain rates. The predicted maximum sustained tensile stress, being consistent with experimental data, follows a three-segment power-law relationship with strain rate, exhibiting a slow-rapid-saturation increase trend. Concurrently, the mechanisms of deformation and failure transition from cavitation-crazing at low strain rates to uniform deformation-interchain decohesion at moderate rates, and ultimately to chain scission at high strain rates. Our detailed analysis indicates that the mismatch between deformation velocity (V-D) and thermal velocity (V-T) of polymer atoms is critical in governing the dynamic tensile behavior. Based on these results, we propose an analytical velocity criterion-specifically, the logarithmic ratio of log(V-D/V-T)-that quantitatively predicts the transition among the three distinct regimes. This study provides significant theoretical insights and molecular-level understanding of the rate-dependent tensile behavior of glassy polymers, offering a foundation for the design and development of advanced polymers capable of withstanding extreme loading conditions.

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