Table 1.
Input and recovery error of non-linear viscoelastic coefficients.
Fig 1.
Non-linear stress-relaxation fits.
The proposed numerical integration direct fit method for non-linear viscoelastic characterization was able to accurately fit the idealized stress-relaxation experimental data, including the non-linear stress-strain behavior during the ramping phase and the strain-dependent relaxation indicative of non-linear viscoelastic behavior.
Fig 2.
Linear stress-relaxation fits.
The linear viscoelastic formulation was not able to capture the idealized strain-dependent stress-relaxation data, resulting in large RMSE values compared to those of the non-linear viscoelastic formulation.
Fig 3.
Non-linear dynamic cyclic fits.
The proposed direct fit method accurately fit the idealized dynamic cyclic response at three frequencies. These curves were fit simultaneously but are plotted separately to improve visualization of the higher frequency fits. Images in the right column show the first cycle of the fit for each frequency.
Fig 4.
The linear viscoelastic formulation was unable to fit the idealized dynamic cyclic response, resulting in very large RMSE values compared to those of the non-linear viscoelastic formulation. These curves were fit simultaneously but are plotted separately to improve visualization of the higher frequency fits. Images in the right column show the first cycle of the fit for each frequency.