Development of Micro-mechanical Constitutive Model for Alumina at High Strain Rates Using Unified Mechanics Theory

Ceramic materials used in mechanical applications show variations in their properties due to the presence of cracks. Micro-cracks within the material (size, orientation and density) affect the ceramic material’s strength and other mechanical properties. This study developed a micro-mechanics-based model that accounts for the original orientation of micro-cracks and their propagation as wing cracks. Unlike other micromechanics-based models, the current model defines failure based on entropy associated with crack propagation within the material. Entropy is calculated from energy dissipation from crack propagation from the pre-existing flaws in the ceramic. The Unified Mechanics Theory (UMT) is used to define entropy-based damage in the ceramic material, in which a parameter called thermodynamic state index (TSI) is employed to describe the state of the material. A representative volume element (RVE) with a pre-existing flaw is used to calculate the energy dissipated during the wing crack propagation. The effect of various crack lengths and orientations is incorporated with a probability density function. The strain rate effects are implemented using dynamic crack growth law. The stress-strain curve at strain rate from quasi-static to high strain rate (10^-3-10⁶) is plotted for Alumina under dynamic compression.