The yielding and the linear-to-nonlinear viscoelastic transition of an elastoviscoplastic material

Abstract

Elastoviscoplastic materials present a transition from a gel-like to a liquidlike state induced by shearing: While the first is primarily elastic, the second is predominantly viscous. The point that characterizes this transition is usually known as the yield point, which is associated to critical quantities such as yield stress and/or yield strain. Another characteristic of elastoviscoplastic materials is the transition from linear to nonlinear viscoelasticity. In the current work, a commercial hair gel, which is an elastoviscoplastic material, was tested in two rotational rheometers in order to evaluate these two transition points. Stress oscillatory amplitude sweeps at different frequencies were performed and a Fourier-Transform analysis was applied to the results in order to determine the linear viscoelastic limit. The linear viscoelastic limit stresses and strains at different frequencies were then compared to quantities that are usually associated to the yield point: The extrapolated zero-shear-rate stress obtained from the equilibrium flow curve, the minimum stress required to start up flows in creep experiments, the stress overshoot reached in constant shear rate experiments and the G′-and-G″ crossover stress determined through oscillatory amplitude sweeps. The results showed that the stresses and strains obtained as the linear viscoelastic limits were smaller than the critical quantities associated to the yield point for all evaluated cases. Although the critical quantities depend on the experimental condition, the linear viscoelastic limit strain was remarkably constant. Additionally, the linear viscoelastic limit strain was found to be in the same order of magnitude of the strain that characterizes the onset of plastic behavior in recovery experiments. This suggests that the beginning of the transition from a completely structured state of elastoviscoplastic materials to an unstructured state might be associated to the threshold of nonlinear viscoelasticity.

Elucidating the G″ overshoot in soft materials with a yield transition via a time-resolved experimental strain decomposition

“…This has led to the predominant description of yielding as being a binary phenomenon, as evidenced by the ubiquity of models in existence with a single yield stress (5,(16)(17)(18)(19)(20). There have been challenges to the existence of a yield stress in the past (5,21), and a number of recent studies (22)(23)(24) have explicitly shown that attempts to define a single yield threshold are ambiguous, at best. Furthermore, the fact that Bingham chose to only investigate the steady-state properties of plastic materials, and did not consider any time dependence, led to the furtherance of the idea that yielding is an instantaneous phenomenon.…”

“…It is now known that the transition requires a finite amount of time to complete (23). As a result, it has been difficult to develop an understanding of the processes and mechanisms (both rheological and microstructural) that occur during yielding (5,7,(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33). This has, in turn, reduced the availability or development of structure-property relations for the yielding transition, which has rendered the tailored design of novel plastic soft materials difficult (10,11).…”

Mechanical Properties of Paste Slurry under Constant Shear Rate in Initial Structure Failure Process

“…Fully immersed the vane rotor in the slurry and rotated at a constant speed, the shear stress was measured as a function of shear strain or time as shown in Figure 2. e curve was divided into two parts: AB segment was the stress rise phase which was the initial structural failure process [20][21][22] and BC segment was the stress decay phase which was the thixotropic process [23,24].…”

Determination of the Yield Stress of Disperse Systems

“…Consequently, we can extend the definition of the yield stress to include all rheological systems-the rheological systems must have a three-dimensional network at low shear rates, but it is not necessary to be an elastic solid. The yield stress can be determined from the region of the flow curve, where the shear stress does not change significantly with the increase of the shear rate [19,[21][22][23][24][25][26][27] by extrapolation of the shear stress to the y-axis.…”