基于CT孔隙岩石三维变形及应变场的数字体图像相关法研究

Research on porous rock damage mechanism and porous structure model are significant to solve practical engineering problems in petroleum industry, geology,mining, metallurgy, civil engineering and hydraulic engineering.In this project,High-Resolution Computer Tomography(CT) combined with Digital Volume Correlation(DVC) is applied to measure the inter-deformation of porous rock under loading.A 3D enriched finite element kinematics which is used in Extended Finite Element(XFEM)to calculate the discontinuous deformation is introduced as an displacement shape function of DVC in order to measure the inter local discontinuous deformation of porous rock.With algorithm optimization and parallel computation,the accuracy,efficiency and robust of DVC are improved. With this high-efficiency DVC, the 3D displacement and strain field of porous rock,such as medium-grained sandstone, red sandstone and oil sands, are acquired and analized,the rules of deformation and damage are researched ,and then the damage mechanism is revealed.From the CT volume images of porous rock,the characteristical parameters are extracted.Combined Monte Carlo and Random Number Algorithm,the porous rock structure models with the same statistic parameters and probability density functions are obtained. Based on the analysis of 3D deformation and strain field from the numerical simulation and experiment, these structure models are made more perfect.This project closely tied the frontiers of rock mechanics and experimental mechanics. The results will provide new idea and new experiment method to porous rock and its structure model researches.

孔隙岩石破坏机理与孔隙结构模型的研究对解决石油、地质、采矿、冶金、土木和水利工程中的实际问题具有十分重要的意义。本课题利用高精度CT扫描技术结合数字体图像相关法，将扩展有限元计算三维非连续变形的富集函数作为数字体图像相关法位移形函数来测量孔隙岩石内部非连续变形；通过算法优化，并行计算提高数字体图像相关法的精度，计算效率与稳定性；测量计算分析孔隙岩石(以中砂岩,红砂岩和油砂岩为主)在不同加载条件下不同阶段的三维位移场及应变场,研究其变形破坏规律，揭示破坏机理；通过孔隙岩石的CT体图像,提取孔隙分布的特征参数,结合Monte Carlo 法和随机数算法生成具有相同统计参数和概率密度函数的孔隙结构模型,比较分析数值模拟与实验所得位移场及应变场,完善孔隙结构模型。本课题选题紧密结合岩石力学与实验力学的前沿领域，为研究孔隙岩石内部变形破坏提借新实验方法，同时为孔隙岩石结构模型研究提供新途径。

孔隙岩石内部变形破坏机理与孔隙结构模型的研究对解决石油、地质、采矿、冶金、土木和水利工程中的实际问题具有十分重要的意义。结合微焦点X射线CT，利用岩石内部非均质及孔隙形成的结构作为天然散斑场，提出了数字体散斑法(Digital Volumetric Speckle Photography, DVSP)测量岩石内部变形场，该方法可看作频率域内实现相关性搜索的数字体图像相关法。在DVSP法中，采用两步快速傅里叶变换，提高了计算效率，通过纯相位滤波器的设计提高相关性搜索的可靠性。结合空间域数字体图像相关法，引入子块体平移技术实现亚体素空间的搜索，提高测量精度，以砂岩为例：考虑噪声与伪影的情况下，测量不准确度为0.03体素。研制了系列与工业CT 配套的加载装置，能够实现单轴拉压、三点弯曲、三轴压缩等多种形式的原位加载扫描。试件尺寸φ25×50mm，分辨为45μm，轴压可达260MPa，围压为40MPa。获得了砂岩、泥岩、煤和混凝土等试件在不同加载条件下的三维体图像，利用DVSP法计算得到试件内部的变形场，实现了的内部变形的可视化。通过应变场的分析，获得了试件内部小于CT分辨尺度微裂隙引起的应变局部化产生及演化过程，揭示了试件破坏特征。通过对砂岩的CT 图像处理与分析，获得了内部孔隙结构及空间分布的统计特征，结合Monte Carlo 和随机数生成方法，建立了不同孔隙率的数值计算模型，对其破坏规律进行了研究。DVSP与CT相结合将会成为岩石实验力学中获取内部变形场的重要的方法。