尺寸效应和应变速率对岩石力学特性影响的试验研究

Effect of the size and strain rate on the mechanical behavior of rock specimens

采用MTS 815.02型电液伺服岩石力学试验系统,对6种规格岩样应变速率在1×10^(-5)~5×10^(-3) s^(-1)范围内进行了6级应变速率下的单轴压缩试验,分析了岩样尺寸、应变速率对岩样峰值强度、弹性模量、峰值应变、声发射特性及破坏形态等力学性质的影响.结果表明,岩样的峰值强度与岩样尺寸呈负相关,与应变速率呈正相关,两者均可采用二次多项式进行描述.当岩样尺寸较小(L/D<2.0)时,岩样声发射振铃数在峰值应力前后呈先逐渐增多后减少的渐变规律,声发射模式属于渐进发射型;当岩样尺寸较大(L/D≥2.0)时,在达到峰值应力之前声发射数量较少,在应力峰值处突然爆发显著的声发射事件,声发射模式属于突跃发射型.当岩样高径比较小(L/D<2.0)时,随着应变速率的增加,岩样的声发射振铃数与振铃次数增多,声发射活动越强烈,岩样破坏形式较为复杂,沿轴向出现较多的劈裂面或岩样产生圆锥形破坏;当岩样高径比较大(L/D≥2.0)时,岩样基本为单一剪切破坏.当应变速率较小(ε′<5×10^(-4) s^(-1))时,岩样破坏形式为剪切破坏或拉剪混合破坏;当应变速率较大(ε′≥5×10^(-4) s^(-1))时,随着应变速率的增加,岩样易产生圆锥形破坏.

In order to well understand the effects of the size and strain rate on measured properties,the uniaxial compression tests of 6samples with different sizes were carried out under 6strain rates ranging from 10^-5 s^-1 to 5× 10^-3 s^-1 using the MTS 815.02electric-hydraulic servo rock mechanics testing system.The results show that the sample size and strain rate significantly affect the peak strength,elastic modulus,peak strain,acoustic emission characteristics and failure pattern of rock samples.Particularly,the peak strength value shows a negative correlation with sample size and a positive correlation with strain rate.The two relationships can be described by aquadratic polynomial function.When the size of the rock sample is small（L/D2.0）,the acoustic emission gradually increases and then decreases before and after the peakstress and acoustic emission,which belongs to the model of gradual emission.When the size of the rock sample is large（L/D≥2.0）,there are relatively few acoustic emission events before the peak stress,but at peak stress,it increases suddenly and dramatically,which belongs to the pop-in emission type.Moreover,the acoustic emission events increase as the strain rate,which implies the enhancement of acoustic emission activities.When the ratio of height to diameter is less than 2.0,the failure pattern of the rock sample is relatively complicated,with a fracture plane appearing along the axial direction;conical failure is also present.When L/D≥2.0,rock samples primarily fail with a single shear failure plane.Atε′〈5×10^-4 s^-1,the rock sample fails in a pattern of shear failure or tensile-shear mixed failure.With an increase in the strain rate（ε′≥5×10^-4 s^-1）,the rock sample tends to fail in a conical failure pattern.