基于原子力显微镜的板岩杨氏模量宏微观跨尺度表征方法研究

Cross-scale characterization of the Young’s modulus of slate using atomic force microscopy

岩石材料的微观非均匀结构和微观力学特性是制约其宏观变形与破坏力学行为的关键因素。针对川藏铁路隧道板岩,采用原子力显微镜测试技术,结合粉晶X射线衍射、扫描电子显微镜和能谱分析技术,获得了板岩纳米尺度下的矿物构像和微观结构,并揭示了微观尺度板岩矿物杨氏模量空间分布;进而采用混合高斯模型对160多万个试验数据进行反卷积分析,确定了高、中、低强度三相的平均杨氏模量和概率;最后基于Mori-Tanaka模型对板岩杨氏模量进行尺度升级,建立了板岩杨氏模量宏微观跨尺度表征方法。结果表明:(1)纳米尺度下板岩中嵌入的石英呈凸面多边形块体,伊利石薄片紧密、定向排列呈明显的层理性,而绿泥石作为基质松散地分布在孔隙中;(2)石英、伊利石、绿泥石和微观孔隙对原子力探针的黏附力依次递增,杨氏模量依次递减;(3)微观测试结果和图像分析表明,板岩孔隙度为16.61%、宏观杨氏模量为56.17 GPa。该方法适用于破碎、小尺度、任意形状岩石的力学参数精细测量分析,为通过饼化、破碎岩芯估算硬岩的宏观杨氏模量等力学参数提供了一种新的技术路线,具有较好的实用价值。

It is essential to expose the rock’s heterogeneous microstructure and micro-mechanical properties for understanding the macroscopic deformation and failure.In this paper,atomic force microscopy(AFM),combined with powder X-ray diffraction(XRD),scanning electron microscopy(SEM)and energy dispersive spectrum(EDS)techniques,is used to analyze the nanoscale mineral composition and microstructure of slate taken from Sichuan-Tibet railway tunnels.The spatial distribution of Young’s modulus is revealed at the microscale.The average Young’s modulus and probability of high,medium and low strength phases are determined by statistical deconvolution of more than 1.6 million test data using a mixed Gaussian model.The upscaling of Young’s modulus of slate is carried out based on the Mori-Tanaka model.A cross-scale characterization method of Young’s modulus is proposed based on the Mori-Tanaka model and micro-mechanical properties of minerals.The results show that:(1)The quartz embedded in the slate is a convex polygon block,the thin illite sheets are closely arranged with obvious stratification,and the chlorite is loosely distributed in the micro-pores as the matrix;(2)The adhesion of quartz,illite,chlorite and micro-pore to the probe increases in turn,and the Young’s modulus decreases;(3)The porosity of slate is 16.61%,and the equivalent Young’s modulus at the macroscale is 56.17 GPa.This approach can be used to determine the mechanical properties of fractured,small-size and arbitrary-shaped hard rock,which can overcome the difficulty of collecting large-size samples of engineering rock.