One of the distinctive features of these experiments is that if the strain or stress is suddenly removed, the system starts to recover. You can switch between the two sets of units. For soft-matter rheology it makes sense to use Pa. ![]() The original papers are "polymer" papers so the key values are in terms of MPa. When b is very small then we have a simple dashpot. A is the response rate or frequency, and b controls the non-linearity. This is the hardening spring made from two components which I've called E 1 & E 11, though in the literature these are called η 1 & η 2. ![]() So it's important to get a feel for what each one means We need 5 parameters for this (rather than the two each for Maxwell and Kelvin-Voigt). The key is that the parallel spring is a "strain hardening" one, with no strength at zero strain, and we use a non-linear "Eyring" dashpot. Here we use a "modified standard solid" model developed by Evagelia Kontou and others 1 which has a spring and dashpot in series plus a spring and (the same) dashpot in parallel. A spring and dashpot in parallel give you a Kelvin-Voigt solid which can simulate Creep but not Relaxation A spring and dashpot in series give you a Maxwell fluid which can simulate Relaxation, but not Creep.
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