岩盤 つくばでの最近の研究 （３） 砂岩のサブクリティカルなクラック成長とそれに基づく引張強度のひずみ速度依存性推定の試み

Abstract

Double torsion tests in ambient air and liquid water have been used to establish stress intensity factor (KI )-crack velocity (V ) diagrams for propagation of single tensile crack in dry or water-saturated sandstones, Kimachi sandstone and Shirahama sandstone. The following main results were obtained: 1) All the experimental data for dry specimens in ambient air and water-saturated specimens in water pertain to region I of the typical KI-V curve, while even region II was clearly observed in KI-V curve of dry specimens tested in water. The appearance of region was particularly clear in Shirahama sandstone. 2) No stress corrosion limit was encountered in the specimens tested in water even at nearly 20 % of critical stress intensity factor (KIC ). But, dry Kimachi sandstone specimen tested in ambient air possibly exhibits the stress corrosion limit at nearly 50 % of critical stress intensity factor (KIC ). 3) The KI-V data of Kimachi sandstone were used to generate a diagram predicting the influence of strain rate on tensile strength. These predictions were in good agreement with the tensile strength determined by Brazilian experiments in ambient air and liquid water. Both the predictions and the experimental results are consistent with a monotonic reduction in tensile strength as strain rate is reduced from nearly 10-2 s-1 to nearly 10-8 s-1.