Synchrotron Studies of Long Range Internal Stresses in Plastically Deformed Materials

非技术总结材料在使用过程中经常会有意或无意地承受载荷或应力。有证据表明，由于材料中原子缺陷的聚集，这些应力在材料中可能不是均匀分布的。这些缺陷负责促进或“携带”材料的正常永久或塑性变形，这些变形是由外部应力引起的。然而，这种应力的重新分布可能导致材料中的长范围内应力(LRIS)。描述和理解导致背应力的长范围内应力的细节和来源至关重要。这将由首席研究员和他的学生在阿贡国家实验室的先进光子源(同步加速器)上使用新的尖端X射线微束表征技术进行研究。了解背应力的来源和大小的细节可以使我们对材料的重要性能方面有一个新的理解。这尤其包括疲劳和金属成形。疲劳是结构材料最常见的灾难性失效机制之一。更好地了解疲劳将导致结构材料性能的提高。了解金属成形操作中的背应力可能会大大节省金属成形制造业的成本。PI还将与洛杉矶中南部高中的外展项目合作。技术概述背应力或长范围内应力(LRIS)在过去被广泛认为存在于塑性变形的结晶材料中。在变形的微结构中，位错密度升高或位错不均匀的区域可能存在升高的应力。长程内应力的存在对于理解循环变形和单调变形尤为重要。X射线微束衍射实验将由首席研究人员和学生使用同步加速器进行，该加速器能够首次确定位错细胞壁和内部的应变。这项工作包括尝试测量细胞内部和细胞壁上的全弹性应变张量。这也将是有史以来第一次进行这种类型的实验。PI还将进行原位微梁实验，并在试件承受外部载荷时测量晶格参数。PI和他的学生将检查严重塑性变形(SPD)材料，这些材料被建议存在相对较高的LRI。这些实验将由国际和平研究所和阿贡国家实验室高级光子源的研究生进行。总的来说，我们对塑性变形的理解有望得到加强。本项目将了解对疲劳很重要的背应力，它是大多数结构材料失效的原因，也是金属成形中回弹的原因。了解金属成形操作中的LRIS可能会在制造业带来巨大的节省。PI还将与洛杉矶中南部高中的外展项目合作。

Non-Technical SummaryMaterials are often intentionally or unintentionally subjected to loads, or stresses, during service. There is evidence that these stresses may not be uniformly distributed in materials due the presence of clustering of atomic defects in the material. These defects are responsible for facilitating or "carrying" the normal permanent or plastic deformation in materials that results from the external stresses. However, this redistribution of the stress can lead to long range internal stresses (LRIS) in materials. It is critical to characterize and understand the details and origin of long range internal stresses that lead to backstresses. This will be researched by the Principal Investigator and his students using, new cutting-edge, x-ray microbeam characterization techniques at the Advanced Photon Source (synchrotron) at Argonne National Laboratory. Learning the details of the origin and the magnitude of the backstresses can lead to a new understanding of important performance aspects of materials. This particularly includes fatigue and metal forming. Fatigue is one of the most common catastrophic-failure mechanisms in structural materials. Better understanding of fatigue would lead to enhanced structural-materials performance. Understanding backstresses in metal forming operations could lead to enormous savings in the metal-forming manufacturing sector. The PI will also work with outreach programs to high schools in south-central Los Angeles. Technical summaryBackstresses or long range internal stresses (LRIS) have been, in the past, widely suggested to exist in plastically deformed crystalline materials. Elevated stresses can be present in regions of elevated dislocation density or dislocation heterogeneities in the deformed microstructures. The existence of long range internal stress is especially important for the understanding of cyclic deformation but also monotonic deformation. X-ray microbeam diffraction experiments will be performed by the principal investigator and students using a synchrotron that are able to determine the strain within dislocation cell walls and interiors for the first time. This work includes an attempt to measure the full elastic strain tensor in the cell interiors and cell walls. This will also be the first experiment ever performed of this type. The PI will also perform in-situ microbeam experiments and measure the lattice parameter while the specimen is under external load. The PI and his students will examine severely plastically deformed (SPD) materials, where relatively high LRIS has been suggested to be present. These experiments will be performed by the PI and graduate students at the Advanced Photon Source at Argonne National Laboratory. Our understanding of plastic deformation, in general, is expected to be enhanced. This project will understand backstresses that are important to fatigue, the cause for most structural material failures, and also spring back in metal forming. Understanding LRIS in metal forming operations could lead to enormous savings in the manufacturing sector. The PI will also work with outreach programs to high schools in south-central Los Angeles.