Improved interpretation of asphalt binder parallel plate dynamic shear rheometer fatigue tests

The time sweep test, consisting of cyclic, torsional loading in the dynamic shear rheometer (DSR), has been employed for the fatigue characterisation of asphalt binders. The parallel plate geometry imposes radially inhomogeneous strain field, which results in a radial inhomogeneous stress field. Past efforts have inferred fatigue damage in DSR tests based on monitoring the apparent edge stress, which is calculated using linear radial mapping to the total torque. The assumption of linear variation in the shear stress response with radial distance from the specimen centre is erroneous of material or geometric nonlinearities such as cracking. To improve the interpretation of parallel plate fatigue tests, a means to account for the non-linear radial gradient in stress response is derived using simplified viscoelastic continuum damage (S-VECD) modelling. The developed methodology is validated through comparison to cone and plate results where the stress state is uniform. The results demonstrate that the developed methodology allows for accurate determination of S-VECD model coefficients using parallel plate testing alone.