CAREER: Towards Fatigue Behavior Prediction of Structural Materials through Computationally-Informed Textural and Microstructural Characteristics

University Of Tennessee Knoxville, Knoxville TN

Investigators

Abstract

This Faculty Early Career Development Program (CAREER) project will integrate mechanics of deformations at multiple length scales to discover how the microstructure of a metal influences the distribution of local stress (force over nominal area) that drive failure under cyclic loading. Failure of structural materials by fatigue -- the accumulation of damage under cyclic loading -- remains one of the major challenges in mechanics and materials science. Crucially, the mechanisms through which applied mechanical loading distributes between regions called grains within the microstructure are not fully understood. The novelty of the computational approach to be used in this project is to explicitly target the grain boundaries, which will inherently connect multiple scales relevant to fatigue crack nucleation and growth. Knowledge of the correlations between the microstructure and fatigue crack driving forces will enable tailored material design. Recent advances in additive manufacturing technology have enabled control of microstructure during material deposition. This research will yield a theoretical and computational framework for designing structural components to capitalize on this flexible manufacturing technology. Thus, the research will advance national health, prosperity, welfare, and defense, while progressing science. The research outcomes of the project will be integrated with specific K-12 and underrepresented minority outreach activities as well as support foundational research in vectors education. Making physics concepts easier will empower students to succeed and bring new perspectives to their future STEM careers. Curriculum enhancements will directly impact courses at the 11th grade up to graduate level; broader impact is achieved through teaching new pedagogies to educators. The goal of this research is to advance the understanding of microstructural and textural influences on fatigue behavior of polycrystalline materials by understanding how stress applied at the bulk scale is redistributed at the grain scale. The primary research objective is to discover how grain interactions, called the neighborhood effect, influence the distribution of local stresses that drive fatigue crack nucleation and growth. The novel approach involves decomposing the balance of forces and displacement jumps along grain boundaries into contributions from the granular uniform field (mesoscale) and fluctuation field (microscale). A multi-resolution Discontinuous Galerkin method is developed to measure the neighborhood effect that is ideally-suited for capturing discontinuities along grain boundaries, allowing contributions from mesoscale and microscale to be distinguished but not having to be separated. Hypotheses are pursued to reveal the relative zone of influence of mesoscale versus microscale stress components, thereby elevating the empirical nature of fatigue threshold design to account for microstructural and textural features that increase resistance to small crack growth. Insight as to how these local effects propagate through the microstructure and affect material fatigue would provide a better understanding of why some flaws nucleate cracks while others do not. This project launches the PI towards becoming a national leader in the prediction of engineering scale fatigue properties for polycrystalline structural materials. 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.