高温后砂岩动力特性应变率效应的试验研究

Experimental study of mechanical properties on strain rate effect of sandstones after high temperature

利用MTS652.02高温炉与φ50 mm分离式霍普金森压杆（SHPB）试验系统,对800℃加热后的砂岩试样进行单轴冲击压缩试验,分析17.904~62.600 s-1应变率范围内砂岩动力特性的变化规律。结果表明：800℃后砂岩动态应力-应变曲线大致经历压密、近似线弹性变形、微裂纹演化、裂纹非稳定扩展、应变软化以及卸载6个阶段;随着应变率提高,砂岩动态弹性模量、峰值应力随应变率的提高基本呈对数形式逐渐增加,峰值应变近似呈对数形式逐渐降低;较低应变率下,砂岩破坏为典型的张拉破坏,随着应变率的升高,剪切破裂面所占比例逐渐升高,砂岩破坏型式具有从张拉破坏向剪切破坏的变化趋势;800℃热处理后,砂岩破坏程度随应变率的提高逐渐提高,并且高应变率下破坏程度的应变率敏感性更加显著。

Dynamic compression test has been performed on sandstones subjected to 800℃ based on split Hopkinson pressure bar （SHPB） and high-temperature furnace MTS652.02. We study the dynamic properties of sandstone specimens whose strain rate varies within the range between 17.904 s ^-1 and 62.600 s ^-1. The test results show that, after heated to 800 ℃, dynamic stress-strain curves of sandstone can be roughly divided into compaction phase, elastic deformation stage, microcracks evolution stage, crack unstable growth stage, strain softening stage and unload stage. With the increasing strain rate, the dynamic elastic modulus and peak stress of sandstone increase with logarithmic trend, while the peak strain decreases with a logarithmic form. The failure mode of sandstone is mainly typical tensile failure in low strain rate, while the proportion of shear fracture surface gradually increases as the increasing of strain rate; failure mode changes from tensile failure to shear failure. Undergoing 800℃ heat treatment, sandstone failure is gradually severe with the elevated strain rate, and the degree of failure is more significant sensitivity at high strain rates.