Rheological fingerprints for a Bautista-Manero-Puig model-variant with Elasto-Visco-Plastic features under a true yield-stress approach

In this work, a new model-variant in the Bautista-Manero-Puig (BMP) model is proposed, with the peculiarity of providing true yield-stress features under vanishing deformation rates. This proposed model is devised to predict an Elasto-Visco-Plastic (EVP) rheological response through the assumption of a null fluidity (infinite viscosity) limit, and inherits the BMP ability to track the material-structure temporal evolution through a thixotropic kinetic equation. This new model, termed BMP-EVP, is systematically compared against the parent original BMP model, which provides solid-like features in an apparent yield-stress modality, through diminishing solvent fractions. The rheological fingerprints of both BMP and BMP-EVP models are exposed and contrasted under typical steady and transient rheometrical tests, under shearing and extensional deformations, alongside oscillatory protocols under Small and Large Angle Oscillatory Shear (SAOS and LAOS, respectively). Here, plasticity is measured through the definition of critical deformations for material fluidisation that appeared explicitly and directly correlated with the BMP thixotropic parameters. Conventional steady-state simple shear and uniaxial extensional flows render the BMP and BMP-EVP models comparable in their material-function predictive capabilities. In contrast, non-linear transient tests show attractive differences across these models, for which secondary loops in LAOS and non-monotonic stress-growth coefficient in start-up flows, evidence the interplay between the thixo-viscoelastic features of these models and their distinct plastic responses.