采用点矩阵纳米压痕技术对渝东南酉阳地区下志留统龙马溪组页岩进行弹性模量、硬度、断裂韧性等力学参数测量,借助场发射扫描电镜和能量色散X射线荧光光谱对压痕形貌及压痕区域矿物组成进行定量分析,提出基于矿物强度分类的三组分页岩微观力学模型,采用Mori-Tanaka方法实现力学参数从纳米向厘米尺度升级,并利用页岩单轴压缩实验结果进行对比分析。实验结果表明,纳米尺度下的页岩弹性模量与硬度、弹性模量与断裂韧性之间具有良好的线性关系,垂直层理方向的页岩弹性模量、硬度、断裂韧性等略小于平行层理方向;力学参数具有Weibull分布特点,硬度结果离散性最强,分析主要为页岩本身非均质性和压痕投影不确定性所导致。对比纳米压痕均值统计、尺度升级模型与宏观单轴压缩实验结果发现,纳米尺度下力学参数结果要高于尺度升级模型和单轴力学实验参数结果,证实不同尺度下的力学参数存在差异性,岩心尺寸越大,包含颗粒间孔隙和内部缺陷越多,则会导致岩石力学参数值减小。图12表5参23
The mechanical properties such as Young’s modulus, hardness and fracture toughness of Lower Silurian Longmaxi shale samples from Youyang area in southeast Chongqing, China were investigatedusingdot matrix nanoindentation measurements. With the help of field emission scanning electron microscope (FESEM) and energy dispersive X-ray fluorescence spectroscopy (XRF), the indentation morphology and mineral composition in indentation area were quantitatively analyzed. According to mechanical strength classification, a micromechanical model with three components was introduced and the Mori-Tanaka model was used to upscale mechanical parameters from nano-scale to centimeter-size scale, which were further compared with uniaxial compression results. The experimental results show that there is a positive linear correlation between Young’s modulus and hardness and between the Young’s modulus and the fracture toughness under nano-scale; the Young’s modulus, hardness and fracture toughness perpendicular to the bedding are slightly lower than those parallel with the bedding. According to data statistics, the mechanical properties at the nano-scale follow Weibull distribution feature and the dispersion degree of hardness results is the highest, which is mainly due to shale anisotropy and nanoindentationprojection uncertainty. Comparing the results from nanoindentation test, with those from upscaling model and uniaxial compression test shows that the mechanical parameters at the nano-scale are higher than those from upscaling model and uniaxial compression test, which proves mechanical parameters at different scales have differences. It’s because the larger the core, the more pores and internal weakness it contains, the less accurate the interpreted results of mechanical parameters will be.
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