Yielding characterization of waxy gels by energy dissipation

The rheological behaviors of yield stress fluids are commonly interpreted from the energy perspective, yet this perspective has rarely been applied for waxy gel. In this study, we calculated the energy dissipated into the waxy gel caused by viscous strain during the deformation process with the aid of a well-tested elasto-viscoplastic thixotropic model. The energy dissipation shows a power-law dependence on the strain regardless of the stress ramping rate. The energy dissipation has been shown to be useful to characterize the ductility of waxy gel, that is, the larger the energy is dissipated during fracture, the more ductile the waxy gel is. When the waxy gel is induced to the same strain by different stress ramping rate, the energy dissipation during the deformation process shows little dependence on the stress ramping rate. However, if during the loading process the stress is increased to the same value by different ramping rate, a higher stress ramping rate causes lower energy dissipation. These findings are helpful to elucidate the widely observed experimental observation for waxy gels that the measured yield stress depends on the stress ramping rate whereas the measured yield strain shows little dependence.