非均质煤样细观力学特性的双轴压缩数值模拟

煤的微观结构特征对煤的力学特性起着重要作用。为了更加真实准确地研究非均质煤样的细观力学特性,首先通过扫描电镜(SEM)获取煤样放大8 000倍的微观结构图像;然后采用数字图像处理技术对SEM图像进行处理,构建能反映煤样较为真实结构特征的CAD矢量结构模型,并将其导入颗粒流离散元软件(PFC)建立符合煤样结构特征的数值模型;最后开展了煤样细观力学特性的双轴压缩颗粒流数值模拟。结果表明:煤作为一种混合物,它所包含的矿物质和微孔裂隙对其力学性能有重要作用;应力应变曲线有明显的峰值转折点,可以分为弹性阶段、应变软化阶段和残余阶段;煤样在双轴压缩条件下产生的宏观裂纹主要受拉伸力影响,其破裂形态不规则;在应力峰值位置附近,裂纹的增长速率最快,此时的颗粒体间平均接触力也最大,能够达到3.25×10⁸N;另外随围压和加载速率增大,应力-应变曲线形式基本保持不变,但轴向应力峰值及裂纹数逐渐增加;应力峰值对应的轴向应变与围压无确定的规律,而与加载速率呈正比关系。

Numerical simulation for the micro-scopic mechanical features of the het-erogeneous coal samples based on the biaxial compression

The given paper is aimed first of all to trace and disclose the micromechanical features of the heterogeneous coal samples authentically so as to obtain the microstructure figures of the coal samples at a size magnification of 8 000 times through the SEM test. The micromechanical features of the coal sample authentic analysis can then be further analyzed by the digital image processing technology so as to preprocess and binary-process their SEM image,and then,to reconstruct more realistic coal sample microstructures. And,so,the CAD vector structure model of the structural features can be transformed into the particle flow dispersion element software( PFC) so as to build up a numerical model in conformity with the structural features of the coal samples under study. And,eventually,the program code can be compiled by using the fish program language in PFC,with the contact constitutive model of the particles set up as a paralleled bonding model to finish the numerical simulation of the micromechanical properties of the coal samples at the biaxial compression condition. The results show that,coal,as a mixture,ought to contain minerals and micro-porous cracks,which can play an important role in its mechanical properties. Their stressstrain curve may have an obvious peak turning point,which can be divided into elastic stage,strain softening stage and residual stage. In such a case,the macrocracks produced by the coal samples under the biaxial compression have been mainly affected by the tensile force,and the fracture morphology may turn out to be irregular under the condition of stress. And,what is more,with the increase of the confining pressure and loading rate,the form of the stress-strain curve has been basically remaining unchanged,though the peak value of the axial stress and the number of cracks may tend to be increasing gradually. Thus,the axial strain in correspondence with the peak stress would not have been definite due to the confining pressure of its own,but can only be proportional to the loading rate. Thus,it can be seen that the above contents may not be integrated with the SEM image directly into the study of the coal deformation and failure behavior. Hence,for what is said above,the modeling method of the particle flow simulation of the mechanical behaviors of heterogeneous coal samples we have brought about can be expected to promote further understanding of the mechanical features of the interior microstructure of the coal under mining in the given mine.