Spall failure of alumina at high-strain rates using femtosecond laser experiments and high-fidelity molecular dynamics simulations

Ceramic materials are widely used in high-strain-rate applications due to their exceptional strength-to-weight ratio. However, under these extreme conditions, spall failure becomes a critical concern, which is driven by a large hydrostatic tensile stress state. This study introduces a novel two-laser setup to generate controlled hydrostatic stress states at specific locations within test specimens. By inducing and manipulating shock wave interactions, we achieve large hydrostatic compressive and tensile stresses at very high-strain-rates, enabling the controlled nucleation and growth of nanovoids leading to spall failure. Our experiments demonstrate that shock wave interference can precisely trigger spallation at arbitrary locations in the specimen thickness. To further validate our approach, we investigate alumina spall failure using molecular dynamics (MD) simulations with a custom-designed graph neural network potential. The MD results show strong agreement with experimentally estimated spall strength. These findings highlight the potential of the two-laser technique as a powerful tool for studying the early stages of spall failure in ceramics, paving the way for advanced materials testing methodologies.