不同断裂模式下低温对砂岩断裂韧度的影响研究

Effect of low temperature on fracture toughness of sandstone under different fracture modes

为了研究不同低温条件下砂岩峰值载荷和断裂韧度的变化规律,对经过低温处理的5组干燥砂岩试件和常温砂岩试件进行半圆盘三点弯曲断裂试验。研究结果表明:低温对不同断裂模式的砂岩试件峰值强度和断裂韧度产生了明显的影响,纯Ⅱ型砂岩试件在20~-60℃的峰值强度和断裂韧度随温度的降低逐渐增大,-80℃时略有下降;纯Ⅰ型和Ⅰ+Ⅱ复合型砂岩试件峰值强度和断裂韧度在20~-20℃随着温度的降低呈增大趋势,-20~-60℃随着温度的降低呈减小趋势。在不同温度条件下,纯Ⅰ型断裂模式的砂岩试件峰值强度最低、断裂韧度K_(IC)最高;Ⅰ+Ⅱ复合型砂岩试件断裂模式的峰值强度与等效断裂韧度K_(eff)均居中;纯Ⅱ型砂岩试件断裂模式峰值强度最高、断裂韧度K_(IIC)最低。K_(IC)与K_(eff)受低温影响的变化幅度较大,K_(IIC)受低温影响的变化幅度最小。

In order to study the variation law of peak load and fracture toughness of sandstone under different low-temperature conditions,five groups of dry sandstone specimens treated at low temperature and normal-temperature specimens were tested by three-point bending fracture test of half disk.The results show that low temperature has an obvious influence on the peak strength and fracture toughness of different fracture modes.The peak strength and fracture toughness of pure mode-Ⅱspecimens from 20℃to-60℃gradually increase with the decrease of temperature,and slightly decrease at-80℃;the peak strength and fracture toughness of pure mode-Ⅰand mixed fracture mode(Ⅰ+Ⅱ)increase with the decrease of temperature from 20℃to-20℃and decrease with the decrease of temperature from-20℃to-60℃.Under different temperatures,the peak strength of pure mode-Ⅰfracture mode is the lowest,and the fracture toughness K_(ⅠC) is the highest;the peak strength and equivalent fracture toughness K_(eff) of mixed fracture mode(Ⅰ+Ⅱ)are in the middle;the pure mode-Ⅱfracture mode of sandstone specimens has the highest peak strength and the lowest fracture toughness K_(ⅡC),K_(ⅠC) and K_(eff) changed in a wider range are affected by low temperatures,and K_(ⅡC) is less affected by low temperatures.