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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Imaging strain localisation in porous andesite using digital volume correlation
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Imaging strain localisation in porous andesite using digital volume correlation

机译：使用数字体积相关性的多孔岩中成像应变定位

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Strain localisation structures, such as shear fractures and compaction bands, are of importance due to their influence on permeability and therefore outgassing, a factor thought to influence eruptive style. In this study, we aim to develop a better understanding of strain localisation in porous volcanic rocks using X-ray tomographic images of samples of porous andesite (porosity = 0.26) acquired before and after deformation in the brittle and ductile regimes. These 3D images have been first analysed to provide 3D images of the porosity structure within the undeformed andesite, which consists of a large, well-connected porosity backbone alongside many smaller pores that are either isolated or connected to the porosity backbone by thin microstructural elements (e.g., microcracks). Following deformation, porosity profiles of the samples show localised dilation (porosity increase) and compaction (porosity reduction) within the samples deformed in the brittle and ductile regimes, respectively. Digital volume correlation (DVC) of the images before and after triaxial deformation was used to quantify the tensor strain fields, and the incremental divergence (volumetric strain) and curl (used as an indicator of shear strain) of the displacement fields were calculated from the DVC. These fields show that strain localisation in the sample deformed in the brittle regime manifested as a similar to 1 mm-wide, dilatational shear fracture oriented at an angle of 40-45 degrees to the maximum principal stress. Pre- and post-deformation permeability measurements show that permeability of the sample deformed in the brittle regime increased from 3.9 x 10(-12) to 4.9 x 10(-12) m(2), which is presumed to be related to the shear fracture. For the sample deformed in the ductile regime, strain localised into similar to 1 mm-thick, undulating compaction bands orientated sub-perpendicular to the maximum principal stress with little evidence of shear. Taken together, our data suggest that these bands formed during large stress drops seen in the mechanical data, within high-porosity zones within the sample, and within the large, well-connected porosity backbone. Pre- and post-deformation permeability measurements indicate that inelastic compaction decreased the permeability of the sample by a factor of similar to 3. The data of this study assist in the understanding of strain localisation in porous volcanic rocks, its influence on permeability (and therefore volcanic outgassing), and highlight an important role for DVC in studying strain localisation in volcanic materials. (C) 2020 Elsevier B.V. All rights reserved.
机译：由于它们对渗透性的影响和偏移来说，应变定位结构（例如剪切骨折和压实带）具有重要性，因此旨在影响喷发风格的因素。在这项研究中，我们的目的是利用在脆性和韧性制度之前和之后获得的多孔骨灰（孔隙率= 0.26）的样品的X射线断层图像更好地了解多孔火山岩中的应变定位。首先分析了这些3D图像以在未变形的洞穴内提供孔隙率结构的3D图像，其包括通过薄的微观结构元件（例如，微裂纹）。在变形之后，样品的孔隙率谱分别显示出局部扩张（孔隙率升高）并分别在脆性和延性制度中变形的样品内的压实（孔隙率降低）。使用三轴变形之前和之后的图像的数字体积相关性（DVC）来量化张量应变场，并且计算出位移场的增量发散（体积菌株）和卷曲（用作剪切应变的指示灯）。 DVC。这些字段表明，在脆性制度中变形的样品中的应变定位表现为与最大主应力为40-45度的角度的类似于1mm宽的，扩张的剪切断裂。预变形渗透率测量表明，在脆性调节中变形的样品的渗透率从3.9×10（-12）增加到4.9×10（-12）m（2），这被推测与剪切有关断裂。对于在延性状态下变形的样品，应变局部地定位成1mm厚的起伏压实带，其取向亚垂直于最大主应力，几乎没有剪切证据。我们的数据结合在一起，建议在机械数据中看到的大应力下降期间形成的这些带，在样品内的高孔隙区内，以及在大连接的孔隙骨架内。后和后后渗透性测量表明，非弹性压实将样品的渗透率降低了类似于3.本研究的数据有助于了解多孔火山岩中的应变局部化，其对渗透性的影响（以及因此火山突出），并突出了DVC在研究火山材料中的应变定位方面的重要作用。 （c）2020 Elsevier B.v.保留所有权利。

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