Application of Novel Structural Finite Elements Implemented Within Combined Finite-Discrete Element Methods

ABSTRACT: Simulating the structural response of concrete and reinforced concrete structures to blast loading conditions is a challenging task, as it requires modeling the fracture and fragmentation processes in this composite material with reasonable computational efficiency for large scale simulations. To address this problem, novel shell formulations have been incorporated within Los Alamos National Laboratory's implementation of the combined finite-discrete element method, called HOSS (Hybrid Optimization Software Suite). In this numerical study, these new finite element formulations are utilized for modeling thin concrete and metal linings for applications in building construction. Both unreinforced and reinforced concrete can be modeled with this method which opens the door for addressing many practical applications. 1. INTRODUCTION Since its inception, the combined finite discrete element method (FDEM) has become a tool of choice to address a variety of problems involving fracture and fragmentation processes in solids. FDEM combines the strengths of the finite element method (FEM) and the discrete element method (DEM). The key advantage of FDEM is the utilization of finite strain-based deformability combined with suitable constitutive material laws which are then merged with discrete element based transient dynamics, contact detection, contact interaction solutions, and objective discrete crack initiation and crack propagation solutions (Munjiza, 2004). The comparison of DEM and FEM with a schematic visualization of FDEM is shown in Fig. 1. In FDEM, the solid bodies are modeled as a collection of deformable particles that are bonded with each other (Rougier et al., 2014), Fig. 1. These solid bodies (called discrete elements) are discretized into finite elements where their finite displacements and rotations are assumed a priori (Munjiza, 2004; Munjiza et al., 2011, 2015). The bonding is numerically represented with cohesion points along the boundaries of the deformable particles (Rougier et al., 2014). The cohesion of these bonds is a combination of normal cohesion and tangential cohesion. When an FDEM model experiences fracture, failure, or fragmentation and the material is exposed to high enough levels of stress, these bonds become increasingly strained until they reach their ultimate strengths and eventually break resulting in the adjacent finite elements to also become unbonded (Rougier et al., 2014). The single discrete element domains are transformed into interacting domains upon which discretized contact solutions can be used for both contact detection and contact interaction (Knight et al., 2020).