CAREER: A Deformation Mechanism-Based Approach to Understanding the Conversion of Plastic Work to Heat and Stored Energy

University Of Utah, Salt Lake City UT

Investigators

Abstract

This Faculty Early Career Development (CAREER) program will address fundamental unresolved issues in the understanding of how mechanical work is converted to heat during rapid deformation events. Current approximations assume ninety percent of mechanical work is converted to heat during deformation due to an incomplete understanding of how nano- and micro-scale deformation mechanisms influence the work to heat conversion process. Computational predictions of material strength and failure during dynamic events, such as rapid metal forming, high-speed machining, and vehicle crash, use the ninety percent approximation, which can be wholly inaccurate. These inaccuracies have potentially hindered the implementation of promising light-weight magnesium alloys as safety critical structural components in automotive, aerospace and railway applications. In this research, a comprehensive understanding of how individual deformation processes contribute to the thermal state of magnesium alloys may allow them to supersede comparatively heavy steel and aluminum components, and thus provide a straightforward path to improved fuel efficiency, reduced emissions, and fuel-cost savings. As part of the project, the PI will also provide hands-on learning opportunities for underrepresented communities in STEM and support the training of undergraduate and graduate students through research in the laboratory. Mechanism-based investigations have the potential to account for experimentally observed strain, strain-rate, and loading mode dependencies of the conversion of plastic work to heat. This project will focus on investigating strain and loading mode dependencies using a textured hot-rolled magnesium alloy AZ31B. Four loading orientations, three grain sizes, and two temperature states are judiciously selected to systematically activate (or suppress) preselected deformation mechanisms, specifically, basal slip, prismatic slip, pyramidal a slip, pyramidal c-a slip, and extension twinning. Specimens will be deformed adiabatically using a split-Hopkinson pressure bar coupled with ultra-high-speed imaging and multi-point IR thermography. Experiments will provide measures of macroscale mechanical behavior, full-field deformation maps, and local temperature evolution. Post-mortem, electron backscatter diffraction and transmission electron microscopy will be leveraged to identify predominant defect arrangements and defect interactions. Collaboratively, these in-situ measurements and post-mortem observations will enable the PI?s laboratory to achieve the project goal to identify individual mechanism contributions to a deforming material?s thermal state. This new knowledge can be incorporated into numerical models to more comprehensively predict material behavior and temperature under adiabatic deformation conditions. 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.