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Mixed-mode (I and II) fracture behavior of a basal-textured magnesium alloy
Acta Materialia ( IF 9.4 ) Pub Date : 2020-07-01 , DOI: 10.1016/j.actamat.2020.03.023
K.V. Vaishakh , R. Narasimhan , K.U. Yazar , S. Suwas

Abstract Mixed-mode (I/II) fracture experiments on rolled AZ31 Mg alloy are conducted using notched four point bend specimens along with in-situ imaging. Digital Image Correlation (DIC) technique is used to analyze the images and map out the deformation and strain fields. With increase in mode II component of loading, a monotonic reduction in the notched fracture toughness (Jc) is observed. Fractographs reveal that the fracture mechanism transitions first from (ductile) micro-void growth and coalescence to twin induced quasi-brittle failure and then to shear cracking as the loading changes from mode I to II. Detailed optical micrographs and EBSD maps show profuse tensile twinning in the ligament, especially near the far-edge of the specimen leading to pronounced texture changes. However, the micro void size near the notch tip as well as the twin density in the ligament reduce with higher mode II component. The pronounced drop in fracture toughness and the changes in the associated mechanism with increase in mode-mixity are rationalized from the combined effects of hydrostatic stress, plastic strain localization and tensile twinning.

中文翻译:

基底织构化镁合金的混合模式(I 和 II)断裂行为

摘要 使用缺口四点弯曲试样和原位成像对轧制 AZ31 镁合金进行了混合模式 (I/II) 断裂实验。数字图像相关 (DIC) 技术用于分析图像并绘制变形和应变场。随着加载的模式 II 分量的增加,观察到缺口断裂韧性 (Jc) 单调降低。断口图显示,随着载荷从模式 I 变为模式 II,断裂机制首先从(延展性)微孔洞生长和合并转变为孪晶诱导的准脆性破坏,然后转变为剪切开裂。详细的光学显微照片和 EBSD 地图显示韧带中有大量的拉伸孪晶,尤其是在样本远缘附近,导致明显的纹理变化。然而,缺口尖端附近的微空隙尺寸以及韧带中的孪晶密度随着模式 II 分量的增加而降低。由于静水应力、塑性应变局部化和拉伸孪晶的综合影响,断裂韧性的显着下降和相关机制随着模式混合度的增加而发生变化。
更新日期:2020-07-01
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