细观尺度下岩石沿晶断裂应力强度因子计算研究

Study of intercrystalline facture stress intensity factor of rock in meso-scale

大量的细观试验研究发现,岩石破坏主要是裂纹沿着岩石晶体颗粒边界的扩展造成的(沿晶断裂),裂纹沿弯折晶界的扩展则构成了不同材料边界上翼裂纹的扩展。基于以上细观试验结果,建立奇异单元的有限元模型,通过对节点位移的数值外插法,得到了岩石材料沿晶断裂翼裂纹应力强度因子,并研究了晶粒几何特征和材料非均质性(Dundurs参数)对裂纹扩展的影响。研究表明:在均质情况下,晶粒的几何形状在接近正六边形的情况下最适合裂纹扩展。随着非均质性的增强,各主翼裂纹比和晶粒几何角度所对应的KI值都要较均质模型的结果更高,最大的KI所对应的晶粒的内角角度也有所增加。综合所有计算结果可以看出,岩石中晶粒的非均质程度越高,越利于岩石破裂。

All naturally formed rocks belong to multicrystal material;and abundant mesascopic experimental studies reveal that the rock failure is mainly caused by intercrystalline fracture which occurs along the boundaries of crystalline grains of the rocks.The extension of the cracks along the kink grain boundaries constitutes the form of winged crack extension among different materials.At present,there are many methods to calculate the winged cracks;and most results are obtained based on equivalent method under the condition of homogeneous medium.This paper establishes the computational process by using ANSYS Parametric Design Language and obtains winged crack tip stress intensity factor at the interface of the intercrystalline fracture via using the numerical extrapolation method for the nodes displacement.Then a comparison is made with the HN approximate calculation model brought forward by H.Horri and S.Nemat-Nasser;the similarities and differences of crack extension between the heterogeneous brittle material and the homogeneous material are analyzed;and also,the influence exerted by the geometrical characteristics of the crystalline grain and the heterogeneity degree（Dundurs parameter） of the material on the crack extension are studied.The result takes the multicrystallinity and heterogeneity of the rocks into consideration and reveals the changing process of the stress intensity factor when the intercrystalline crack extends in the rock.