基于VMIB的岩石围压破坏二维多尺度数值模拟

VMIB (Virtual Multi-dimensional Internal Bonds)模型是在VIB(Virtual Internal Bond) 模型基础上发展起来的一种多尺度力学模型.VIB认为,固体材料在微观上是由随机分布的质量微粒(Material particle)构成,微粒与微粒之间由一虚内键(virtual internal bond)连结,材料的宏观本构方程则直接由微粒之间的连结法则(Cohesive law)导出.而在VMIB中,微粒之间引入了切向效应,材料的宏观本构方程由虚内键刚度系数导出.由于考虑了微粒之间的切向效应,VMIB能够再现材料不同泊松比.依据VMIB,材料的宏观力学行为决定于微观虚内键的演化.岩石材料在围压条件下强度显著增强,破坏模式一般表现为剪切破坏,其微观机制在于虚内键的演化决定于自身的法向和切向变形,并且演化速度决定于连续层次上材料微元的应力状态.为描述这种微观虚内键的演化机制,提出了一种虚内键演化方程.通过该演化方程,可以宏观再现岩石材料在围压条件下的断裂破坏行为.作为初步应用,没有考虑材料的塑性变形机制,因此,还有待于进一步的理论完善.

2-D multiscale numerical simulation of rock failure subjected to confining pressure based on virtual multi-dimensional internal bonds

The virtual multi-dimensional internal bonds(VMIB) is a multiscale mechanics model developed from the virtual internal bond(VIB). VIB considers solid material to consist of randomized ‘material particles’ in microscopic. The material particles are connected with virtual internal bond. The macro constitutive relation is derived from a given cohesive law between material particles. Different from VIB, a shear effect is introduced into the interaction between material particles in VMIB and the macro constitutive relation is derived in terms of bond stiffness. Owing to accounting for the shear effect, VMIB can present the diversity of Poisson ratio. According to VMIB, the macro response of material results from the micro bond evolution. The mechanical resistance of rock material subjected to confining pressure is considerably strengthened and the failure under such conditions is usually of the shear kind. The underlying micro mechanism of these macro presentation is that the evolution of bond stiffness is governed by the normal and shear deformation of bond itself while the evolution velocity is subjected to the stress state of the microelement at the continuous level. To describe this micro evolution mechanism of bond, a phenomenological evolution function of bond is proposed. By this evolution function, the fractures of brittle materials subjected to confining pressure can be simulated. However, as a tentative application, the presented method couldn’t represent the plastic flow phase in the complete stress-strain relationship since the plastic deformation is not accounted.