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

该学院早期职业发展(Career)计划将解决在快速变形事件中如何将机械功转换为热的基本悬而未决的问题。目前的近似假设是90%的机械功在变形过程中被转换为热，这是因为对纳米和微米尺度的变形机制如何影响功到热的转换过程的了解不够深入。在动态事件中，如快速金属成形、高速加工和车辆碰撞，材料强度和失效的计算预测使用90%的近似值，这可能是完全不准确的。这些不准确潜在地阻碍了在汽车、航空航天和铁路应用中作为安全关键结构部件的前景光明的轻质镁合金的实施。在这项研究中，全面了解单个变形过程如何影响镁合金的热状态，可能会使它们取代相对较重的钢和铝组件，从而为提高燃料效率、减少排放和节省燃料成本提供一条直接的途径。作为该项目的一部分，PI还将为STEM中代表性不足的社区提供实践学习机会，并通过实验室研究支持本科生和研究生的培训。基于机制的调查有可能解释实验观察到的应变、应变率和将塑料功转换为热量的加载模式相关性。本项目将使用织构热轧镁合金AZ31B来研究应变和加载模式的相关性。合理地选择了四种加载方向、三种晶粒度和两种温度状态，以系统地激活(或抑制)预先选定的变形机制，特别是基面滑移、棱柱滑移、金字塔a滑移、金字塔c-a滑移和伸展孪生。样品将使用分离式霍普金森压杆结合超高速成像和多点红外热像仪进行绝热变形。实验将提供宏观力学行为、全场变形图和局部温度演变的测量。将利用尸检、电子背向散射衍射和透射电子显微镜来确定主要的缺陷排列和缺陷相互作用。通过协作，这些现场测量和尸检观察将使皮？S实验室能够实现项目目标，以确定对变形材料-S热态-的个别机制贡献。这一新知识可以被纳入到数值模型中，以更全面地预测绝热变形条件下的材料行为和温度。这一奖项反映了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。

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.