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

表面声波(SAW)普遍存在于许多自然发生的破坏性现象中，如地震和海啸。此外，长期以来，锯子一直被认为是导致船舶螺旋桨空化、高速撞击风力涡轮机叶片以及喷射气流使岩石破碎而造成表面损坏的原因之一。在新兴的医疗应用中，如纳米脉冲碎石术，SAW也被认为在确保患者成功地非侵入性粉碎肾结石方面发挥了至关重要的作用。尽管如此，锯子在材料表面引发断裂的基本机制在很大程度上仍不清楚。这并不是一个孤立的现象，因为无论加载类型如何，裂纹的形核和扩展都是几十年来一直令人头疼的问题。在此背景下，该奖项支持基础研究，以解释反复使用锯子和其他动态载荷如何导致脆性材料表面的裂纹成核并影响其随后的生长。来自该项目的见解将对寻求理解和预测一个仍然难以捉摸的基本现象的科学家和工程师大有裨益：脆性材料在普遍的机械载荷作用下开始损伤。拟议的研究是跨学科的，将工程师和计算科学家聚集在一起，全面探索这类问题。重要的是，它还包括旨在鼓励高中和本科生STEM领域中代表性不足的少数族裔学生从事材料力学研究的外联活动。尽管断裂领域最近在理论上取得了进展，但目前对固体中裂纹形核及其向扩展的转变的科学理解仍然不完整和探索不足。本研究主要对脆性材料在多种条件下重复加载下裂纹的形核和扩展进行了实验、理论和计算研究。将研究两个原型系统：浸入水中并承受多重冲击载荷的材料和承受反复冲击载荷的干燥材料。新的实验将在玻璃和Begostone上进行，Begostone是一种工程材料，其弹性、强度和韧性特性可以在很大范围内方便地变化。这些实验将与基于新的连续统理论的模拟一起进行，该理论将把惯性效应和低周疲劳纳入裂纹形核和扩展的统一模型。这些研究的结果将揭示一个长期悬而未决的基本问题，即低周疲劳和惯性载荷如何降低材料系统的强度和韧性，并最终导致它们在任意机械载荷下的断裂和失效。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.