(a) Strain sweep test. The region of linear viscoelasticity was first
assessed. When materials are tested in their linear range, in fact,
their characteristics do not depend on the magnitude of the stress
ordeforming strain, or the rate of application of the strain (Steffe,
1996). The linear domain limit, determined from the strain sweep
test, was 0.05% strain for all the samples. Beyond this limit, both the
elastic modulus (G0) and the viscous modulus (G00) decreased and,
as a result, tand increased (curves not reported). G0 and G00 are parts
of the complex modulus, G* ðG* ¼
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
ðG0Þ2 þ ðG00Þ2
q
Þ, reported in
Fig. 3a. In general, beyond the limit of 0.05% strain a progressive
dismantling of the original structure of the matrices was observed,
indicating that variations in the rheological properties of the
different doughs became dependent on the magnitude of the strain
imposed. NS-D and SL-D showed similar G* values, higher than
those exhibited by the other samples. A small difference was
observed between FR-D and SC-D, being G* higher in FR-D, thus
suggesting a prevalence of the elastic response. These behaviors
reflected those highlighted by the farinographic measurements,
even if in that case the deformations applied were much larger.