These findings are consistent with previous studies that found that extensional thickening stabilizes film blowing for polyethylene and bubble blowing for bubble gum, a trait necessary for bubble gums but not chewing gums. The one exception was sample B2 with a maximum stress % 3.0 Â 10 5 Pa, reminiscent of a typical chewing gum. To be quantitative, the peak extensional stresses of bubble gums were > 2.0 Â 10 6 Pa versus 2.0 Â 10 6 Pa for chewing gums. Bubble gums typi- cally sustained larger stresses and had more significant strain hardening than commercial chewing gums. This conclusion is supported by the observation of decreasing G 1 00 along with the negative leading-order viscous third-harmonic v 3 1). Similarly, we find that the viscous features of the critical gel network are also disrupted by large strain rates. Quantitatively, this elastic concavity corresponds to positive third-harmonic Chebyshev coefficient e > 0, and we interpret this as elastic softening driven by large strain rate, i.e., at this frequency, large strain rates are disrupting the elastic features of the critical gel network. In the context of the global elastic softening of G 1 0, the concavity of the decomposed elastic stress curve shows that the most extreme local softening occurs at locally large values of shear rate (which occur at zero local strain, since they are out of phase).

The concavity of the decomposed stresses, represented at leading order by the signs of third-harmonic Chebyshev coefficients, indicate if these deviations are driven by locally high rates or high strains, as outlined by Ewoldt and Bharadwaj (2013) (their Fig. We interpret higher-harmonics to mean that local elastic energy storage and local viscous energy dissipation are changing through the deformation cycle (i.e., oscillating about the cycle-averaged values of the first-harmonics). All gum materials tested showed qualitatively similar shapes to the Lissajous curves in Fig. At this strain amplitude, the total stress curves are nonelliptical (and the decomposed stresses nonlinear), indicating that higher-harmonic nonlinearities are present.

The right Lissajous curve is normalized shear stress versus strain rate (the viscous perspective), and the dotted line is the decomposed viscous stress, a single-valued function of stress versus strain rate. is normalized shear stress versus strain (the elastic perspective), with the dashed line showing the decomposed elastic stress, a single-valued function of stress versus strain defined by Cho et al.

Grape bubble gum strain