权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

Microscopic Study on Mechanisms of Brittle Fracture and Ductile Deformation in Rocks under High Confining Pressures.

高围压下岩石脆性断裂和延性变形机制的微观研究。

基本信息

批准号：
61540289
负责人：
SHIMADA Mitsuhiko
金额：
$ 1.41万
依托单位：
Kyoto University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1986
资助国家：
日本
起止时间：
1986 至 1987
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-61540289/
关键词：
Rock High confining pressure Microscopy Microcrack Brittle fracture mechanism Scale effect on strength Cataclastic ductile flow カタクラッチック延性流動室温延性流動機構

项目摘要

Microstructures of four brittle-fractured rocks and a cataclastically-deformed rock were studied. They were compared with the mechanical properties which had been observed in the triaxial experiments up to 3 GPa confining pressure at room temperature.Fracture mechanism of four low-porosity rocks (granite, gabbro, dunite and eclogite) changed from the low- to high-pressure types when the compressive strength became equal to the frictional strength. The low-pressure type exhibited the equivalent features to the well-documented brittle fracture. The high-pressure type was different from it: the strength increases linearly at lower increasing rate with increasing confining pressure; the AE activity does not increase rapidly before fracture but stays constant followed by a sudden final fracture; and microcracks are not concentrated close tothe main fault being sharp and oriented at 45 to the maximum stress direction. The high-pressure type fracture might correspond to the transitional one between brittle and ductile regimes, considering the similarity in the faulting features to those found in high temperature experiments. Estimated size effect on strength under pressure gave the suggestion that fracture in the crust might be of the high-pressure type which earthquakes should be modeled upon. Possible faulting processes in the crust including the first faulting and movement of exisiting faults were modeled.A dry fine-grained basalt with 7% porosity, in the ductile regime, exhibited cataclastic deformation behavior. In the progressive stage of granulation at higher stress levels, the flow mechanism was found to change from the power-law creep with stress exponent of 3 to 1 at 2 GPa confining pressure. It was found to results from the remaining-pore closure and pervasion of highly granulated portions. The viscosity drop of -10^5 Pa・s was estimated associated with the mechanism change at the strain rate corresponding to that for the crust and mantle.

研究了四种脆性破裂岩石和一种碎裂变形岩石的显微结构。与室温下围压达3GPa的三轴实验结果进行了比较，发现当岩石的抗压强度与摩擦强度相等时，四种低孔隙度岩石（花岗岩、辉长岩、纯橄榄岩和榴辉岩）的断裂机制由低压型向高压型转变。低压型表现出与有据可查的脆性断裂相当的特征。高压型与之不同：强度随围压的增加呈线性增加，但增加速率较低; AE活动在破裂前并不迅速增加，而是在破裂后保持不变;微裂纹不集中在主断层附近，且尖锐，与最大应力方向成45 °角。考虑到断裂特征与高温实验中发现的相似性，高压型断裂可能对应于脆性和韧性之间的过渡型断裂。对压力下强度的尺寸效应的估计表明，地壳中的断裂可能是高压类型的，地震应该以这种类型为模型。结果表明，该地区一个孔隙度为7%的干细颗粒玄武岩在韧性体系中表现出碎裂变形行为。在颗粒化的进展阶段，在较高的应力水平，流动机制被发现改变从幂律蠕变与应力指数为3至1在2 GPa围压。结果表明，这是由于高粒化部分的孔隙封闭和扩散造成的。在对应于地壳和地幔应变速率的应变速率下，粘度下降约为-10^5Pa·s，这与机制变化有关。