In situ evaluation of deformation and failure in pure metals and alloys

金属和合金是影响能源生产和分配、运输、民用基础设施和国防等各个行业的最重要的工程材料之一。鉴于这些行业在经济中所起的巨大作用，科学和工程界非常需要提高结构和材料设计的效率和可靠性。这就需要开发这些材料的机械变形和破坏行为的可靠预测模型，这些模型可以与结构和材料设计的定量方法以及安全性和可靠性评估结合使用。提出的努力将通过结合使用定量显微镜和数值模拟技术来深入研究材料的表征和建模。该研究将利用最近开发的实验工具来表征材料在多个长度尺度上的行为，并将它们与计算模型相结合，以极大地提高我们预测工程应用中材料的机械变形和失效的能力。这项研究还将通过学生的参与影响STEM领域的教育和人力资源开发；一名研究生将攻读博士学位，而一到两名本科生将被介绍到材料研究作为该计划的一部分。本研究将把金属材料变形和损伤的多尺度定量实验表征与建模和仿真相结合。提出的研究的主要假设是：多晶材料的变形是通过亚晶尺度上的非均匀变形（离散滑移）发生的；我们假设持续的（和不断发展的）非均质性——即变形的波动而不是平均场变形——决定了这些材料的变形，特别是破坏。因此，研究工作的目的是一方面与定量测量相结合，一方面发展变形和破坏的机制理解，另一方面发展微观结构驱动的模型。研究项目的主要任务如下：(1)对选定的金属材料和合金进行原位SEM实验，识别、了解和量化其变形和破坏机制。（ii）开发/校准宏观尺度的现象学模型以及基于连续塑性的力学模型、代表性体积模型和基于异质模型的离散位错动力学模型。为此，将研究两种纯金属（铜和钽）和两种工程合金（Al 5083, Ti6Al4V）的行为。

Non-technical summaryMetals and alloys form one of the most important classes of engineering materials that affect various industries such as energy production and distribution, transportation, civil infrastructure, and national defense. In view of the large role these industries play in the economy, there is a great need in the scientific and engineering community for improving the efficiency and reliability of structural and material design. This requires the development of robust predictive models of the mechanical deformation and failure behavior of these materials that can be used in conjunction with quantitative methods of structural and material design, and safety and reliability assessment. The proposed effort will delve into material characterization and modeling through the combined use of quantitative microscopy and numerical simulation techniques. The research will leverage on recently developed experimental tools for characterization of material behavior at multiple length scales and combine them with computational models to advance greatly our ability to predict mechanical deformation and failure in materials used in engineering applications. This research will also influence education and human resource development in the STEM areas through the involvement of students; one graduate student will work towards a doctoral degree while one or two undergraduate students will be introduced to materials research as part of the program. Technical SummaryThe proposed research will integrate quantitative multiscale experimental characterization of deformation and damage in metallic materials with modeling and simulation. The main hypothesis of the proposed investigation is the following: deformation in polycrystalline materials occurs through heterogeneous deformation (discrete slip) at the subgrain scale; we postulate that the persisting (and evolving) heterogeneities - i.e., the fluctuations in the deformation rather than the mean-field deformation - dictate the deformation and particularly failure of these materials. Hence, the research effort is aimed at developing a mechanistic understanding of deformation and failure coupled with quantitative measurements on the one hand, and developing microstructurally motivated models on the other hand. The main tasks of the research project are as follows: (i) to perform in situ SEM experiments on selected metallic materials and alloys to identify, understand, and quantify the deformation and failure mechanisms. (ii) to develop/calibrate macroscale phenomenological as well as mechanistic models based on continuum plasticity, representative volume models, and discrete dislocation dynamics based heterogeneous models. Towards this end, the behavior of two pure metals (copper and tantalum) and two engineering alloys (Al 5083, Ti6Al4V) will be investigated.