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首页> 外文期刊>Materials Science & Engineering. A, Structural Materials: Properties, Microstructure and Processing >Cyclic stress-strain response and dislocation structures in polycrystalline aluminum
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Cyclic stress-strain response and dislocation structures in polycrystalline aluminum

机译：多晶铝的循环应力-应变响应和位错结构

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摘要

Fully reversed strain-controlled fatigue tests were performed on polycrystalline specimens of commercially 99.0 percent purity aluminum. The objective was to reveal the influence of plastic strain amplitude and fatigue cycles on dislocation arrangements and investigate the role of dislocation structures on cyclic deformation behavior of aluminum. The test specimens were cylindrical in shape having an effective gauge length section 6.5 mm in diameter and 25 mm long. The fatigue tests were run using symmetrical tension-compression loading under constant strain amplitude in laboratory air environment and room temperature. The longitudinal strain amplitudes used for the testing were in the range of 1.0 X 10~(-3) - 1.1 X 10~(-2) with a constant strain rate of 0.0001 s~(-1). Cyclic deformation behavior was characterized by analyzing the cyclic hardening response, and microstructural observations by means of transmission electron microscopy. The cyclic stress-strain curve of polycrystalline aluminum is characterized with the occurrence of cyclic strain hardening at which the saturation stress increases with plastic strain at all plastic strain amplitudes tested. In addition, the cyclic stress-strain behavior obtained in this study showed grain size dependence, which is in agreement with an equivalent Hall-Petch effect of grain size on cyclic deformation behavior. An investigation on the effect of changing strain amplitude on cyclic hardening reinforces the analysis that dislocation cell structures control fatigue properties. In all strain ranges investigated, microstructures are mainly formed by dislocation cells due to high stacking fault energy, which favors an activation of multiple glide systems and formation of three-dimensional dislocation structures. Persistent slip bands and labyrinth structures were not observed. The observed dislocation cellular structures are low energy structures, which govern plastic hardening (saturated stress) behavior of commercial purity polycrystalline aluminum.
机译：在市售99.0％纯度的铝的多晶试样上进行了完全反向的应变控制疲劳测试。目的是揭示塑性应变幅度和疲劳周期对位错排列的影响，并研究位错结构对铝循环变形行为的作用。测试样品是圆柱形的，具有有效的标距长度部分，直径为6.5mm，长为25mm。在实验室空气环境和室温下，在恒定应变振幅下，使用对称的拉伸压缩载荷进行疲劳测试。用于测试的纵向应变幅度在1.0 X 10〜（-3）-1.1 X 10〜（-2）的范围内，恒定应变率为0.0001 s〜（-1）。通过分析循环硬化响应，并通过透射电子显微镜观察微观结构，表征了循环变形行为。多晶铝的循环应力-应变曲线的特征在于发生了循环应变硬化，在该循环应变硬化曲线下，在所有测试的塑性应变幅度下，饱和应力均随塑性应变而增加。另外，在这项研究中获得的循环应力-应变行为显示出晶粒尺寸依赖性，这与晶粒尺寸对循环变形行为的等效霍尔-帕奇效应一致。关于改变应变幅度对循环硬化的影响的研究加强了位错胞结构控制疲劳性能的分析。在所有研究的应变范围内，由于高的堆垛层错能，微结构主要由位错单元形成，这有利于多重滑移系统的激活和三维位错结构的形成。没有观察到持久的滑带和迷宫结构。观察到的位错细胞结构是低能结构，可控制商业纯度多晶铝的塑性硬化（饱和应力）行为。

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