Determine the cause of the near-vertical stress drop at load reversal

Determine whether a machine response time governs the nearly vertical decrease in measured stress immediately after load reversal during high-rate uniaxial compression of the digitally mixed Agilus–Vero polymers.

Background

The constitutive model does not reproduce the almost vertical stress decrease observed in the experiments immediately after load reversal at higher strain rates. Instead, the model predicts a steep unloading slope followed by nonlinear reverse flow. The authors suspect that the discrepancy is caused by the response time of the testing machine rather than by the material constitutive behavior, but they were unable to verify this explanation. Establishing the origin of this transient response would clarify whether the discrepancy reflects experimental apparatus dynamics or a missing feature of the constitutive model.

References

We suspect a machine response time governs this near-vertical drop, but could not confirm it.

— Composition-dependent nonlinear viscoelastic-viscoplastic behavior and constitutive framework for digitally mixed polymers spanning the glass transition  (2609.04399 - Shen et al., 3 Sep 2026) in Section 5.1, “Intermediate mixtures across the transition” (within Section 5, “Model evaluation across compositions and rates”)