Mo Chengyang, Wisner Brian, Cabal Mike, Hazeli Kavan, Ramesh K T, El Kadiri Haitham, Al-Samman Talal, Molodov Konstantin D, Molodov Dmitri A, Kontsos Antonios
Theoretical & Applied Mechanics Group, Department of Mechanical Engineering, Drexel University, Philadelphia, PA 19104, USA.
Hopkins Extreme Material Institute, John Hopkins University, Baltimore, MD 21218, USA.
Materials (Basel). 2016 Aug 6;9(8):662. doi: 10.3390/ma9080662.
The Acoustic Emission of deformation twinning in Magnesium is investigated in this article. Single crystal testing with combined full field deformation measurements, as well as polycrystalline testing inside the scanning electron microscope with simultaneous monitoring of texture evolution and twin nucleation were compared to testing at the laboratory scale with respect to recordings of Acoustic Emission activity. Single crystal testing revealed the formation of layered twin boundaries in areas of strain localization which was accompanied by distinct changes in the acoustic data. Testing inside the microscope directly showed twin nucleation, proliferation and growth as well as associated crystallographic reorientations. A post processing approach of the Acoustic Emission activity revealed the existence of a class of signals that appears in a strain range in which twinning is profuse, as validated by the in situ and ex situ microscopy observations. Features extracted from such activity were cross-correlated both with the available mechanical and microscopy data, as well as with the Acoustic Emission activity recorded at the laboratory scale for similarly prepared specimens. The overall approach demonstrates that the method of Acoustic Emission could provide real time volumetric information related to the activation of deformation twinning in Magnesium alloys, in spite of the complexity of the propagation phenomena, the possible activation of several deformation modes and the challenges posed by the sensing approach itself when applied in this type of materials evaluation approach.
本文研究了镁中形变孪晶的声发射。将结合全场变形测量的单晶测试，以及在扫描电子显微镜内进行的多晶测试（同时监测织构演变和孪晶形核）与实验室规模的测试在声发射活动记录方面进行了比较。单晶测试揭示了应变局部化区域中分层孪晶界的形成，这伴随着声学数据的明显变化。显微镜内测试直接显示了孪晶的形核、增殖和生长以及相关的晶体学重取向。声发射活动的后处理方法揭示了一类信号的存在，这类信号出现在孪晶大量出现的应变范围内，原位和非原位显微镜观察验证了这一点。从这种活动中提取的特征与可用的力学和显微镜数据以及在实验室规模下为类似制备的试样记录的声发射活动进行了互相关。总体方法表明，尽管传播现象复杂、可能激活多种变形模式以及传感方法本身在应用于此类材料评估方法时带来挑战，但声发射方法仍可提供与镁合金中形变孪晶激活相关的实时体积信息。
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