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

非技术概述金属和合金是影响能源生产和分配、交通运输、民用基础设施和国防等各个行业的最重要的工程材料类别之一。鉴于这些行业在经济中发挥的巨大作用，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。这就需要开发出这些材料的机械变形和失效行为的稳健预测模型，这些模型可以与结构和材料设计以及安全和可靠性评估的定量方法结合使用。拟议的工作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。这项研究将利用最近开发的用于在多个长度尺度上表征材料行为的实验工具，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使用的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；作为该项目的一部分，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领域。技术概述拟议的研究将把金属材料变形和损伤的定量多尺度实验表征与建模和模拟相结合。研究的主要假设如下：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(和演化)的非均质性--即变形中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，这项研究的目的是一方面发展对变形和破坏的力学理解并结合定量测量，另一方面发展微观结构激励模型。研究项目的主要任务如下：(I)对选定的金属材料和合金进行原位扫描电子显微镜实验，以识别、了解和量化变形和破坏机制。(Ii)开发/校准基于连续介质塑性、代表性体积模型和基于离散位错动力学的非均质模型的宏观尺度唯象模型和力学模型。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.