EFFECT OF DEFORMATION RATE ON THE STRESS-STRAIN CURVES OF GELATIN GELS

We studied the large deformation theology of gelatin gels as a functio n of shear rate (shear deformation) and compression speed (compressive deformation). We fitted experimental stress-strain curves using the p henomenological BST equation and extracted: moduli, breaking stretch a nd stress, and a parameter that characterizes the non-linear elastic b ehaviour at large deformations (the elasticity parameter n). The resul ts could be explained in terms of a mechanism in which rupture of the cross-links is not instantaneous. However, the maximum in the degree o f non-linearity of the stress-strain curve (i.e. in n) as a function o f deformation rate is more difficult to explain, especially the decrea se at higher rates. Apparently, some kind of selection mechanism makes the elastic response of the gel more linear at high deformation rates . We propose that this is due to a combination of the fact that the sh ortest cross-links break earlier than the longer cross-links at these high deformation rates and the fact that the network bonds are non-lin ear elastic bonds.