基于单元质心对应法花岗岩热开裂及变形模拟研究

Meso-structure based numerical simulations of deformation and failure of granite: Thermal-mechanical coupling

基于SEM所获取的岩石非均质数字图像,提出了一种既能考虑预制和原生缺陷,又能近似反映材料非均匀性的三维细观结构有限元模型的方法,即单元质心对应法.应用该方法进行了热力耦合下岩石的热开裂及变形破坏数值模拟.结果表明,北山花岗岩热开裂临界温度大约为82℃,与实验值68～88℃基本吻合.低温时北山花岗岩热开裂以沿颗粒热开裂为主;而高温后既有沿颗粒热开裂,又有穿颗粒热开裂.温度的升高导致花岗岩由脆性向延性转变,破坏将由低温下以载荷裂纹为主的裂纹模式转为高温下以热裂纹为主的裂纹模式.对比实验结果发现,数值模拟得到的拉伸强度在低温下高于实验测试值,而中高温度下基本与实验结果吻合.

Scanning electron microscopy （SEM） was used to obtain non-homogeneous digital images of rocks. The corresponding element mass centroid method has been presented to estab- lish three-dimensional finite element model of rock based on SEM images in this paper. This method considers existing defects and approximates a truly non-homogeneous micro-structure characteristic of geo materials. Simulation of thermal-mechanical coupling on thermal cracking and failure in Beishan granite has been done. Thermal cracking in the granite is theoretically estimated to occur at 82 ~C, in good agreement with our recent experimental estimate of 68 to 88 ~C. Inter-granular thermal cracking is the main cracking mechanism at low temperatures. In this case cracks propagate along mineral grain boundaries. At high temperatures the cracking mechanism is a trans-granular coupled with an inter-granular mechanism. Deformation changes from brittle, at low temperatures, to ductile at high temperatures. Crack distributions at final failure change from that typical of low temperature, a load failure, to those typical of high tem- perature, namely thermal failure. Numerical predictions are higher than the experimental load at failure when working at low temperatures. However, the numerical predictions and experi- mental results are in good agreement at higher temperatures.