Eventos Anais de eventos
ENCIT 2016
16th Brazilian Congress of Thermal Sciences and Engineering
Experimental investigation of the yielding of an elastoviscoplastic material
Submission Author:
Rubens Rosario Fernandes , PR
Co-Authors:
Rubens Rosario Fernandes, Diogo Elias da Vinha Andrade, Admilson Franco, Cezar Otaviano Ribeiro Negrao
Presenter: Rubens Rosario Fernandes
doi://10.26678/ABCM.ENCIT2016.CIT2016-0138
Abstract
Elastoviscoplastic materials present a transition from a gel-like to a liquid-like state induced by shearing: while the first is predominantly elastic, the second is predominantly viscous. The point that characterizes this transition is usually known as the yield point, which is traditionally associated to critical quantities such as a yield stress and a yield strain. The viscoelastic nature of elastoviscoplastic materials also leads to another characteristic transition from the linear to nonlinear viscoelasticity. In the present study, a commercial hair gel, which is a non-thixotropic elastoviscoplastic material, was tested in two rotational rheometers. Constant shear rate start-up tests and stress oscillatory amplitude sweeps at different frequencies were performed, aiming to characterize the linear viscoelastic limiting strain. This critical strain was determined as the limit of validity of the linear viscoelastic Maxwell model in the case of start-up experiments, and through a Fourier-Transform in the LAOS transient data for the oscillatory sweeps. Finally, the linear viscoelastic limiting strain was compared to the yield strain, which has been reported in literature as associated to the overshoot stress in constant shear experiments and to the crossover of G′ and G′′ in oscillatory amplitude sweeps. The results show that the linear viscoelastic limiting strain is smaller than the yield strain for all the evaluated cases, and although the yield strain varied through the different experimental conditions, the linear viscoelastic limit strain was remarkably constant. Also, the linear viscoelastic limit strain coincided with the strain in which irreversibilities were first observed in recovery experiments performed after successive steps on the strain. This suggests that the yielding process of elastoviscoplastic materials might be associated to the onset of nonlinearities of the viscoelastic behaviour rather than to the point in which the viscous behaviour overcomes the elastic one.
Keywords
Rheology, Elastoviscoplasticity, yield point, linear viscoelastic limit, critical quantities, Rheology, Elastoviscoplasticity, yield point, linear viscoelastic limit, critical quantities
