Towards a Fundamental Basis for Controlling Shear Flow Instabilities in HCP Metals

为控制 HCP 金属剪切流不稳定性奠定基础

• 批准号: 1610094
• 负责人: Kevin Trumble
• 金额: $ 45万
• 依托单位: Purdue University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-09-01 至 2020-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1610094&HistoricalAwards=false
• 关键词: Towards; Fundamental; Basis; Controlling; Shear

Non-Technical Abstract When metals are deformed to large strains they often undergo a transition from smooth, steady flow to unstable flow modes, which are usually undesirable. Shear banding, in which the strain becomes concentrated in highly localized bands is one mechanism for the flow instability. Another mechanism, recently discovered, is sinuous flow, which is characterized by a folding process near surfaces, analogous to vortex-like fluid flow. These instabilities can cause failure during the deformation itself, as well as leave behind defects that initiate failure in service. They are thus of critical importance in product quality for a wide range of applications (e.g., biomedical, automotive and aerospace). The instability phenomena will be characterized in model metal systems (magnesium, titanium, zinc) using a controlled shear deformation apparatus, in concert with direct, high-speed imaging of the microscopic flow fields and image analysis. Complementary ex situ characterization of the flow will be done using advanced microscopy methods, and low-load indentation. The experiments will be coupled with analytical and numerical modeling to develop flow mechanism maps that depict the various instabilities and the conditions of their occurrence. The research will provide a fundamental basis for developing methods of broad applicability for controlling flow instabilities in advanced metals, advance experimental techniques for flow analysis, and facilitate understanding of other types of instability phenomena in nature. The research results will broadly impact synthesis of metal structures for energy absorption, friction and wear, metals processing and discrete products manufacturing. Complementing the research is an education program involving undergraduate and graduate students in creating a video gallery of flows in materials; and a modest focus on fostering entrepreneurship in graduate study. Technical Abstract The proposed research seeks to advance our understanding of meso-scale plastic flow instabilities in large-strain deformation of metals, and how these instabilities mediate transitions from laminar to unsteady fluid-like flows, e.g., shear band, sinuous and serrated flows. Prior work has established a suite of experimental techniques to characterize flow fields at high resolution that will be built upon in this work. Three coordinated thrusts will study flow instabilities at the meso-scale to establish a fundamental basis for controlling unsteady flows. First, key flow attributes will be mapped, combining direct in situ analysis at high spatial and temporal resolution, with complementary ex situ characterization by microscopy and profilometry. Second, modeling approaches will be developed to describe the flow instabilities and development of unsteady flow dynamics. Third, by integrating the experimental results with model analyses, a phase diagram will be constructed for flows, demarcating unstable regimes and flow transitions in terms of quantitative deformation parameters. The study will be conducted specifically on model HCP alloys (Mg, Ti and Zn) selected for their experimental suitability and range of deformation responses. The resulting flow phase diagram will provide a basis for tailoring and controlling simple-shear flows, from suppressing flow instabilities to enhancing unsteady flows for energy dissipation. The research will foster an education program involving graduate and undergraduate students in developing video galleries to illustrate diverse flow and instability phenomena; student internships in research labs; and graduate student entrepreneurship.

当金属变形为大型菌株时，非技术抽象通常会经常从光滑，稳定的流动到不稳定的流量模式过渡，这些模式通常是不受欢迎的。剪切带浓缩在高度局部带中是流动不稳定性的一种机制。 最近发现的另一种机制是弯曲的流动，其特征是表面附近的折叠过程，类似于涡流样流体。 这些不稳定性可能会在变形本身期间导致故障，并留下启动服务失败的缺陷。因此，对于广泛的应用（例如生物医学，汽车和航空航天），它们在产品质量中至关重要。 不稳定性现象将在模型金属系统（镁，钛，锌）中使用受控的剪切变形设备进行表征，并与微观流场的直接高速成像和图像分析一起进行。流动的互补现场表征将使用高级显微镜方法和低负载压痕进行。 实验将与分析和数值建模相结合，以开发流动机制图，以描述各种不稳定性及其发生条件。 这项研究将为开发用于控制高级金属中流动不稳定性的广泛适用性方法的基本基础，用于流动分析的提前实验技术，并促进对自然界中其他类型的不稳定性现象的理解。研究结果将广泛影响金属结构的合成，以吸收能量，摩擦和磨损，金属加工和离散产品制造。补充这项研究的是一项教育计划，涉及本科生和研究生创建材料流的视频库；并适度地关注培养研究生研究的企业家精神。技术摘要拟议的研究旨在促进我们对金属大型变形中的中尺度塑料流量不稳定性的理解，以及这些不稳定性如何介导从层流到不稳定流体样流的过渡，例如，剪切带，弯曲和锯齿状的流。先前的工作已经建立了一套实验技术，以在这项工作中建立的高分辨率以高分辨率来表征流场。 三个协调的推力将在中尺度研究流动不稳定性，以建立控制不稳定流动的基本基础。首先，将映射键流属性，将直接原位分析在高空间和时间分辨率下结合，并通过显微镜和辅助学来互补的外部表征。其次，将开发建模方法来描述不稳定流动动力学的流动不稳定性和开发。第三，通过将实验结果与模型分析整合在一起，将根据定量变形参数来构建一个相图，以流量为流，划定不稳定的制度和流动过渡。该研究将专门针对用于实验性适用性和变形响应范围的模型HCP合金（MG，TI和ZN）进行。 所得的流相图将为剪裁和控制简单剪切流的基础，从抑制流量不稳定性到增强不稳定的流量以耗散能量。 这项研究将培养一项涉及开发视频画廊的毕业生和本科生的教育计划，以说明多样化的流动和不稳定现象；研究实验室的学生实习；和研究生企业家精神。