Yield Strength Determination Based on Dissipative Energetic Transition: Theory and Validation on Rock Analogue

Mechanical yield strength is one of the most crucial rock properties to consider to remain operating underground in safe elastic regimes. Despite its importance, it remains ambiguous to measure as different disciplines acknowledge different definitions. Most common examples include the deviation from linear elasticity or the peak stress. This difference has significant consequences for the modelling of non-linear deformations since the yield point is the foundation of most plasticity models. We seek to find a criterion that is not empirical in comparison to most but based instead on energetic considerations. Indeed, the transition from elastic to plastic regime corresponds to a transition of energy dissipation. The energy potential we introduce for our new definition of the yield is based on equilibrium theory which states that instability happens when the second derivative of potential energy goes to zero. Practically, we measure this point in time where the maximum of the derivative of the mechanical work is found. The method is examined for numerical simulations and experiments on 3D-printed idealised rock samples. It shows similarities to the traditional offset method in uniaxial compression but is more accurate and differs at high confinements in the compaction cap. It exhibits consistency with the other energetic yield criterion of Gurson. In the future, we aim to make it a new experimental standard for mechanical testing on rocks.