不同温度热处理后砂岩三点弯曲的断裂特性

通过三点弯曲试验研究了不同温度影响下小尺度砂岩试件的断裂特性,证实温度的影响是明显的.125℃是个临界温度点,此时不仅砂岩的平均断裂韧性达到最大值,而且这时砂岩的裂纹扩展模式也发生了根本性的变化,即低温(低于125℃)热处理后砂岩的断裂以沿颗粒断裂机制为主;而高温(大于125℃)热处理后的砂岩的断裂以破断颗粒和沿颗粒的混合断裂机制为主.在100℃-150℃的温度范围内,砂岩的力学特性变得不稳定,这可能是由于粘土物质内部部分吸附水及层间水的蒸发使得粘土物质孔隙结构发生了变化及力学行为变得不稳定所造成的.从125℃到600℃,砂岩的断裂韧性整体有下降趋势,有约50%的降幅,这不仅与温度影响了粘土物质与矿物的胶结情况有关,也与高温处理后砂岩表面出现的热开裂有关,还与因矿物颗粒及粘土物质的热学性质差异导致冷却后存在的残余应力相关.

INVESTIGATION ON FRACTURE CHARACTERISTICS OF SANDSTONE AFTER THERMAL EFFECTS THROUGH THREE-BENDING POINT EXPERIMENTS

The aim of this paper is to investigate the influence of temperature on fracture behavior of sandstone through three-point bending test with pre-crack.The paper indicates that the effects of temperature on sandstone fracture behavior are obvious.And the temperature of 125℃ is a critrical point.At this point,the average fracture toughness of sandstone reaches maximum,and the crack propagation mode also change.Namely,the intergranular fracture mechanism and the mix fracture mechanism of intergranular and transgranular dominate before and after the effects of 125℃,respectively.In the domain of 100-150℃,the mechanical behavior of sandstone is unstable.The main reasons maybe that the change of pore structure and mechanical behavior of clay material due to the evaporation of internal adsorbed water and interlayer water.From 125℃ to 600℃,the average fracture toughness of sandstone decrease approximately 50%.Some potential reasons,such as the effects of temperature on the consolidation degree between clay and minerals,thermal cracking on sandstone,and the residual stress due to the different thermal property of mineral particles and clay materials after cooling,have been discussed in the paper.