A study on the boundary of linear viscoelasticity in simple shear flows: model calculations

Linear viscoelastic region is important to investigate material properties. We investigated boundary of linear viscoelasticity for simple shear flows with various time functions of shear strain. We used Phan-Thien and Tanner (PTT) model and Giesekus model in order to extract the linearity criterion. We determined critical strain (γc) as a function of dimensionless number such as De or Wi and the nonlinear parameter of the models. We found a superposition of the critical strain at start-up shear flow and oscillatory shear flow. Replacing relaxation time by mean relaxation time ( $$\left({\overline {\rm{\lambda }} = {J_{\rm{e}}}{{\rm{\eta }}_{\rm{o}}}} \right)$$ ), we checked the validity of the equation with experimental data.