Idrissi Hosni, Samaee Vahid, Lumbeeck Gunnar, van der Werf Thomas, Pardoen Thomas, Schryvers Dominique, Cordier Patrick
Institute of Mechanics, Materials and Civil Engineering UCLouvain Louvain-la-Neuve Belgium.
Electron Microscopy for Materials Science University of Antwerp Antwerp Belgium.
J Geophys Res Solid Earth. 2020 Mar;125(3):e2019JB018383. doi: 10.1029/2019JB018383. Epub 2020 Mar 7.
The determination of the mechanical properties of serpentinites is essential toward the understanding of the mechanics of faulting and subduction. Here we present the first in situ tensile tests on antigorite in a transmission electron microscope. A push-to-pull deformation device is used to perform quantitative tensile tests, during which force and displacement are measured, while the evolving microstructure is imaged with the microscope. The experiments have been performed at room temperature on 2 × 1 × 0.2 μm beams prepared by focused ion beam. The specimens are not single crystals despite their small sizes. Orientation mapping indicated that several grains were well oriented for plastic slip. However, no dislocation activity has been observed even though the engineering tensile stress went up to 700 MPa. We show also that antigorite does not exhibit a purely elastic-brittle behavior since, despite the presence of defects, the specimens accumulate permanent deformation and did not fail within the elastic regime. Instead, we observe that strain localizes at grain boundaries. All observations concur to show that under these experimental conditions, grain boundary sliding is the dominant deformation mechanism. This study sheds a new light on the mechanical properties of antigorite and calls for further studies on the structure and properties of grain boundaries in antigorite and more generally in phyllosilicates.
确定蛇纹岩的力学性质对于理解断层作用和俯冲作用的力学机制至关重要。在此，我们展示了首次在透射电子显微镜中对叶蛇纹石进行的原位拉伸试验。使用推挽式变形装置进行定量拉伸试验，在此过程中测量力和位移，同时用显微镜对演化中的微观结构进行成像。实验是在室温下对通过聚焦离子束制备的2×1×0.2μm的梁进行的。尽管试样尺寸小，但它们并非单晶。取向映射表明，有几个晶粒的取向有利于塑性滑移。然而，即使工程拉伸应力高达700MPa，也未观察到位错活动。我们还表明，叶蛇纹石并不表现出纯粹的弹性脆性行为，因为尽管存在缺陷，但试样仍积累了永久变形，且未在弹性范围内失效。相反，我们观察到应变集中在晶界处。所有观察结果都一致表明，在这些实验条件下，晶界滑动是主要的变形机制。这项研究为叶蛇纹石的力学性质提供了新的认识，并呼吁对叶蛇纹石以及更广泛的层状硅酸盐中晶界的结构和性质进行进一步研究。
