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

金属和合金是最重要的工程材料之一，影响着能源生产和分配、交通运输、民用基础设施和国防等各个行业。鉴于这些行业在经济中发挥的巨大作用，科学和工程界迫切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失效行为的鲁棒预测模型，这些模型可以与结构和材料设计以及安全性和可靠性评估的定量方法结合使用。拟议的努力将深入研究材料表征和建模，通过结合使用定量显微镜和数值模拟技术。这项研究将利用最近开发的实验工具，在多个长度尺度上表征材料的行为，并将它们与计算模型联合收割机相结合，大大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;一名研究生将攻读博士学位，而一名或两名本科生将被介绍给材料研究作为该计划的一部分。 技术总结拟议的研究将整合定量多尺度实验表征的变形和金属材料的损伤与建模和仿真。所提出的研究的主要假设如下：多晶材料中的变形通过亚晶粒尺度的非均匀变形（离散滑移）发生;我们假设持续（和演变）的非均匀性-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，特别是失效。因此，研究工作的目的是一方面发展一种对变形和失效的机械理解，另一方面发展微观结构模型。该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SEM实验，以识别，理解和量化变形和失效机制。(ii)开发/校准宏观尺度的现象学以及基于连续塑性，代表性体积模型，和离散位错动力学基于异质模型的机械模型。为此，将研究两种纯金属（铜和钽）和两种工程合金（Al 5083，Ti6 Al 4V）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.