Collaborative Research: A Unified Theory of Crack Nucleation and Growth for Materials Subjected to Repetitive Surface Acoustic Waves and Dynamic Impacts

Surface acoustic waves (SAWs) are prevalent in many naturally occurring destructive phenomena, such as earthquakes and tsunamis. Further, SAWs have long been speculated to contribute to surface damage produced by cavitation on ship propellers, high-speed impact on wind turbine blades, and fragmentation of rocks by jetting streams. In emerging medical applications, such as Nano-Pulse Lithotripsy, SAWs have also been postulated to play a vital role in ensuring the success of noninvasive disintegration of kidney stones in patients.

Despite this, the fundamental mechanisms by which SAWs trigger fracture on the surface of materials remain largely unknown. This is not an isolated phenomenon as the nucleation and propagation of cracks regardless of the loading type has been a vexing problem for decades. In this context, this award supports fundamental research to explain how the repeated application of SAWs and other dynamic loadings can give rise to the nucleation of cracks on the surface of brittle materials and affect their subsequent growth.

Insights from this project will significantly benefit scientists and engineers seeking to understand and predict a fundamental phenomenon that has remained elusive: the onset of damage in brittle materials in response to mechanical loads at large. The proposed research is interdisciplinary, bringing together engineers and computational scientists to fully explore this class of problems.

Importantly, it also includes outreach activities designed to encourage under-represented minority students in STEM fields at the high school and undergraduate levels to pursue research in mechanics of materials.

Despite recent theoretical progress in the field of fracture, the current scientific understanding of crack nucleation and its transition to growth in solids remains incomplete and under-explored. This research is focused on the experimental, theoretical, and computational study of crack nucleation and growth in brittle materials in response to repeated, dynamic loadings under a wide range of conditions.

Two prototypical systems will be studied: materials that are submerged and subjected to multiple shock loadings that also cause SAWs, and dry materials that are subjected to repeated impact loads. New experiments will be conducted on both glass and Begostone, an engineered material whose elasticity, strength, and toughness properties can be conveniently varied over a substantial range.

The experiments will be carried out in conjunction with simulations based on a new continuum theory that will incorporate inertial effects and low-cycle fatigue into a unified model of crack nucleation and growth. The results of these studies will shed light on the fundamental yet long-unresolved question of how low cycle fatigue and inertial loads can degrade the strength and toughness of material systems and ultimately result in their fracture and failure in response to arbitrary mechanical loads.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.