著者

小林 良二 酒井 昇 松木 浩二

出版者

一般社団法人 資源・素材学会

雑誌

日本鉱業会誌 (ISSN:03694194)

巻号頁・発行日

vol.99, no.1140, pp.81-86, 1983-02-25 (Released:2011-07-13)

参考文献数

12

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It is well known that rocks are more or less deteriorated by sudden cooling after being heated. Furthermore, by repeating the cycle of heating-cooling, rocks might be expected to be weakened more severely.In this paper, measuring the changes of the physical and mechanical properties of rocks including apparent specific gravity, P-wave velocity, Young's modulus and uniaxial compressive strength, the thermal fatigue process of rocks is characterized for four kinds of rocks, namely, OGINO tuff, EMOCHI welded tuff, AKIYOSHI marble and INADA granite. The cylindrical specimens are suddenly submerged into water after being heated and the cycle is automatically repeated in the testing machine.The maximum temperature and the maximum cycles in the experiment are 600°C and 54, respectively.The main results obtained are as follows:(1) The main failure mechanism is different between the crystalline rock and the sedimentary rock. The failure of the former takes place by the thermal interaction between minerals and that of the latter by the transient thermal stresses. As the result, crystalline rocks collapse to be particles or powders and sedimentary rocks are fractured initiating regular thermal cracks (Fig.6).(2) The strengths of the rocks except welded tuff decrease remarkably within 5 cycles if the temperature is sufficiently high and the cooling time is larger enough (Fig.3).(3) The strengths of the rocks except marble decrease as the cooling time increases. However, the additional effect is very small if the cooling time is larger than that needed for the specimens to be perfectly cooled (Fig.4).(4) The cycles at which the specimens collapse exponentially increase as the temperature decreases (Fig.5).

著者

松木 浩二 狩野 祐一 坂口 清敏 木崎 彰久

出版者

一般社団法人資源・素材学会

雑誌

Journal of MMIJ (ISSN:18816118)

巻号頁・発行日

vol.126, no.12, pp.668-678, 2010-11-25 (Released:2011-11-25)

参考文献数

26

被引用文献数

1 1

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Using joint elements for a mechanical model of grain boundaries, we performed a preliminary 3D finite element analysis of uniaxial tensile fracture for specimen models of monomineral polycrystalline rock under the assumption that fracturing occurs only at the grain boundaries. The specimen models were created on a computer by the method previously proposed by the authors, and the constitutive law of the grain boundaries was derived by applying the associated flow rule in the plastic theory and a tension-shear-softening curve to an extended Coulomb criterion. Tensile fracturing initiates at grain boundaries with a small angle of the normal direction relative to the loading axis, which are followed by grain boundaries with a larger angle of the normal direction. Unloading of intergranular cracks occurs before the peak strength when the intergranular cracks do not compose the final failure plane that is completely formed near the inflection point of the axial stress-axial strain curve after the peak. During the completion of the final failure plane, the conversion of failure mode from tension to shear occurs at intergranular cracks that have a large angle of the normal direction relative to the loading axis. For these intergranular cracks, the axial displacement given at an end of the specimen is converted to a shear displacement, rather than an opening displacement, and the normal stress becomes to be compressive due to shear dilation. Furthermore, the number of tensile intergranular fracturing at the peak strength increases with a decrease in the constant α that characterizes the rate of decrease in the tensile strength in the tension-shear-softening curve of the grain boundaries, and as a result, the tensile strength of the rock specimen increases with a decrease in the constant α. However, the effect of the residual frictional coefficient is small and limited to the stage after the final failure plane is completely formed, since the residual friction coefficient affects the mechanical behavior of the grain boundaries only after the failure plane is completely formed.