Synchrotron Studies of Long Range Internal Stresses in Plastically Deformed Materials

非技术摘要材料在使用过程中经常有意或无意地承受载荷或应力。 有证据表明，由于材料中存在原子缺陷簇，这些应力可能不会均匀分布在材料中。这些缺陷负责促进或“承载”由外部应力引起的材料中的正常永久或塑性变形。然而，这种应力的重新分布可能会导致材料中产生长程内应力 (LRIS)。 表征和理解导致背应力的长程内应力的细节和起源至关重要。 首席研究员和他的学生将在阿贡国家实验室的先进光子源（同步加速器）中使用新的尖端 X 射线微束表征技术来研究这一问题。了解背应力的起源和大小的细节可以使人们对材料的重要性能方面有新的理解。 这尤其包括疲劳和金属成型。 疲劳是结构材料中最常见的灾难性失效机制之一。更好地了解疲劳将有助于提高结构材料的性能。了解金属成形操作中的背应力可以为金属成形制造行业带来巨大的节省。该项目负责人还将与洛杉矶中南部的高中开展外展项目。技术摘要 过去，人们普遍认为塑性变形晶体材料中存在背应力或长程内应力 (LRIS)。变形微结构中位错密度或位错异质性升高的区域中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其重要。 X射线微束衍射实验将由首席研究员和学生使用同步加速器进行，该实验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的全弹性应变张量。这也将是此类类型的首次实验。 PI还将进行原位微束实验并测量样品在外部负载下的晶格参数。 PI 和他的学生将检查严重塑性变形 (SPD) 材料，这些材料被认为存在相对较高的 LRIS。这些实验将由 PI 和研究生在阿贡国家实验室高级光子源进行。总体而言，我们对塑性变形的理解有望得到加强。该项目将了解对疲劳很重要的背应力，这是大多数结构材料失效的原因，也是金属成型中的回弹。了解金属成形操作中的 LRIS 可以为制造业带来巨大的节省。该项目负责人还将与洛杉矶中南部的高中开展外展项目。

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.