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

该学院的早期职业发展（CAREER）计划将解决在理解机械工作如何在快速变形事件期间转换为热量方面的基本未解决问题。目前的近似假设百分之九十的机械功在变形过程中转化为热，这是由于对纳米和微米尺度变形机制如何影响功到热转化过程的不完全理解。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百分之九十的近似值，这可能是完全不准确的。这些不准确性潜在地阻碍了有前途的轻质镁合金作为汽车、航空航天和铁路应用中的安全关键结构部件的实施。在这项研究中，全面了解各个变形过程如何影响镁合金的热状态，可以使它们取代相对较重的钢和铝部件，从而为提高燃油效率、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，应变率和加载模式对塑性功转换为热的依赖性。本项目将重点研究使用织构化热轧镁合金AZ 31 B的应变和加载模式依赖性。四个加载方向，三个晶粒尺寸，和两个温度状态被明智地选择系统地激活（或抑制）预选变形机制，具体地说，基底滑移，棱柱滑移，金字塔滑移，金字塔C-滑移，和延伸孪晶。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成像技术对样本进行热变形。实验将提供宏观尺度的力学行为，全场变形图，和局部温度演变的措施。尸检，电子背散射衍射和透射电子显微镜将被用来确定主要的缺陷排列和缺陷相互作用。合作，这些原位测量和尸检观察将使PI？的实验室，以实现该项目的目标，以确定个别机制的贡献变形材料？的热态。这一新的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。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值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.