Interface and embedded joint methods for modeling dynamic fracture opening by explosive products

Abstract

Two computational approaches are proposed in the paper to model dynamic fracture opening by explosive products. The first method assumes that the fractures may be modeled using flow elements embedded along the mesh lines.This method models crack opening in a straightforward way by splitting the nodes of the computational grid. It can account for crack branching; however, the crack directions are constrained by existing mesh faces, which may lead to mesh dependence. Also, the stress in flow elements is calculated explicitly separate from the surrounding solid elements that can impose additional limits on the time step stability condition for explicit integration. The second approach uses embedded flow elements to model the cracks. Typical thickness of the cracks is much smaller than the element size. Therefore, gas pressure in the cracks is assumed to be in stress equilibrium with the element stress. To achieve this, the crack thickness and the state of the gas is updated simultaneously with the state of the solid element which contains the crack. Therefore, the time step is controlled by the explicit solver applied for the solid and does not depend on the thickness of the crack. The main disadvantage of the second approach is due to the complexity of modeling multiple intersecting cracks, which go through the same element. We discuss the areas of possible applications of these 2 methods and the ways to improve and enhance them for future practical applications.

Simulation of discrete cracks driven by nearly incompressible fluid via 2D combined finite‐discrete element method

“…18 The limitation of this type of coupling approach is that the critical time step required by the explicit integration algorithm is dominated by the size of the fluid elements needed to properly resolve the flow through the fractures. 19 Since, in most cases, the fluid elements are relatively small, the critical time step needed to resolve fluid transport can be several orders of magnitude smaller than the one for the solid. In order to circumvent this issue, and with the aim of improving the efficiency of the code, the authors adopted a "sub-stepping" scheme in the time integration, which uses different time step sizes for the two solvers.…”

“…For example, Fu et al proposed an explicitly coupled hydro‐geomechanical model where the finite volume method was combined with FDEM code and used to model the fluid behavior . The limitation of this type of coupling approach is that the critical time step required by the explicit integration algorithm is dominated by the size of the fluid elements needed to properly resolve the flow through the fractures . Since, in most cases, the fluid elements are relatively small, the critical time step needed to resolve fluid transport can be several orders of magnitude smaller than the one for the solid.…”