Probability Density Function of Dislocation Free Path Length: Experimental Determination through GND Measurements

技术总结：位错平均自由程长度是理解所有相关长度尺度塑性变形的统一概念。直接解释位错运动的塑性公式是随机过程，因为位错的非确定性行为与固体力学的确定性方程相结合。平均自由程长度（MFPL）仅部分成功地量化位错自由程长度。还需要量化位错自由程长度的概率密度函数（PDF）。 本研究的总体目标是通过实验测量位错自由程长度的MFPL和PDF，并将它们与单个晶体滑移系中塑性剪切应变的变形量联系起来。进行这种测量的概念已经存在了几十年，但直到现在才有能力进行这种实验。该计划将开发和使用的方法和程序，使这些实验测量。在这种情况下，本提案的总体教育目标不仅是公布研究目标的结果，而且还公布基本的力学概念以及向更大的研究界进行此类研究所需的实验方法和程序。国家基础设施和运输系统的安全性和可靠性取决于科学家和工程师预测材料，特别是金属，用来建造这些基础设施。由于存在称为位错的缺陷，金属会发生机械故障，这些缺陷在金属内部移动时会导致永久变形。该项目的目标是测量金属永久变形时位错移动的平均距离和距离变化，并将这些量与发生的变形量联系起来。这些量对于预测金属失效的理论的发展和验证非常重要。对金属缺陷运动的新的基本理解有可能导致更好的理论，以更高的保真度预测国家基础设施中材料的行为。该项目的主要教育目标是通过技术文章以及科学会议上的教学研讨会向工程师和科学家介绍进行测量所需的新概念和方法。博士学位学生将在这个项目中得到支持，从而提高国家的人力资源。

TECHNICAL SUMMARY:The dislocation mean free path length is a unifying concept in understanding plastic deformation across all pertinent length scales. Plasticity formulations that account directly for the motion of dislocations are stochastic processes because of the non-deterministic behavior of dislocations combined with the otherwise deterministic equations of solid mechanics. The mean free path length (MFPL) succeeds only partially in quantifying the dislocation free path length. It is also necessary to quantify the probability density function (PDF) of the dislocation free path length. The overall research objective of this proposal is to measure experimentally the MFPL and the PDF of dislocation free path length and relate them experimentally to the deformation quantity of plastic shear strain in individual crystallographic slip systems. The concept of making such measurements has existed for several decades, but the capabilities to perform such experiments have not existed until now. This program will develop and use the methods and procedures to make these experimental measurements. In that context, the overall educational objective of this proposal is to promulgate not only the results from the research objective, but also the underlying mechanics concepts as well as experimental methods and procedures necessary to perform research of this type to the larger research community.NON-TECHNICAL SUMMARY:The safety and reliability of the nation's infrastructure and transportation systems depend upon the ability of scientists and engineers to predict the behavior of materials, especially metals, used to build that infrastructure. Metals experience mechanical failure due to the presence of defects called dislocations that cause permanent deformation as they move throughout the interior of the metal. The goal of this project is to measure the average distance and the variation in distances that dislocations travel as metals are deformed permanently and to relate these quantities to the amount of deformation that occurred. These quantities are very important for the development and validation of theories that predict the failure of metals. New fundamental understanding of the motion of defects in metals has the potential to lead to better theories that predict the behavior of materials in the nation's infrastructure with greater fidelity. The main educational goal of this project is to introduce the novel concepts and methods necessary to make the measurements to engineers and scientists through technical articles as well as teaching seminars at scientific conferences. A Ph.D. student will be supported in this project, thus enhancing the nation's human resources.