Segmental orientation in plastically deformed glassy PMMA

Strain hardening of polymer glasses: Effect of entanglement density, temperature, and rate

“…A recent experimental result 48 is consistent with our observation of strain hardening for chains with N < N e . Wendlandt et al found that the level of segmental orientation during plastic strain well below T g is indicative of an effective constraint density much higher than the entanglement density in the melt.…”

Viscoplasticity and large-scale chain relaxation in glassy-polymeric strain hardening

“…A key difference from most previous theories is that instead of invoking entanglements, we relate the timescale τ for large scale chain relaxation to the segmental relaxation time τ α . This is consistent with: (i) the picture that stress arises predominantly from local plasticity [12], (ii) recent dielectric spectroscopy experiments indicating connections between relaxations on small and large scales [13], and (iii) recent NMR experiments [14] that have found the effective "constraint" density for deformed glasses is much larger than the entanglement density measured in the melt. By relating strain hardening to interactions on the scale of monomers and segments, we make a novel prediction of its magnitude.…”

“…This value is much closer to the effective constraint density measured in (NMR) experiments of deformed glassy samples [14] than to the entropic prediction G R = ρ e k B T . It must be noted that increasing l K also increases ρ e [52].…”

The Influence of Molecular Orientation on the Yield and Post‐Yield Response of Injection‐Molded Polycarbonate

“…The fact that no influence of preorientation above T g is observed on the post-yield response at temperatures below T g can be rationalized by the results of Wendlandt et al [35] . They found by solid-state NMR for PMMA that the finite deformation, both above and below T g , can be described by an affine deformation scheme of entanglement points, albeit that the scale of affine deformation is significantly smaller below T g than above T g .…”

“…No clear picture of the physics behind the strainhardening response of polymers below T g exists, although the search for its origin receives a lot of attention both from experimental and continuum modeling approaches, [21,25,[31][32][33][34][35] as from direct atomistic modeling. [36][37][38][39] Currently, the most frequently used approach for describing the strain-hardening behavior is by using a rubber-elastic spring, [40] with or without finite extensibility.…”