Extending the Discrete Element Method to Account for Dynamic Confinement and Strain-Rate Effects for Simulating Hard Impacts on Concrete Targets

Concrete plays a pivotal role as a foundational material in critical infrastructure, particularly in nuclear plants. Given the imperative for robustness and safety in such contexts, the design of concrete structures necessitates methodologies capable of precisely predicting damage resulting from impacts. When subjected to impact, concrete experiences high loading rates and significant triaxial stresses in the vicinity of the impacting object, potentially resulting in fragmentation, pore closure and projectile penetration. In addressing these challenges, the discrete element method (DEM) emerges as a suitable approach primarily due to its inherent ability to model discontinuities such as cracking and fragmentation. Within this framework, DEM employing spherical discrete elements (DE) has been implemented into Europlexus, a fast transient dynamics finite element (FE) code. This paper presents a refined constitutive DEM model for concrete, especially accounting for porosity closure under high confinement and the effect of strain-rate on tensile strength and fracture energy. The calibration of constitutive parameters is conducted through the simulations of a series of quasi-static (QS) tests encompassing tension, compression and triaxial compression. The strain-rate dependency parameters are identified through dynamic tensile tests conducted using a split-Hopkinson pressure bar apparatus. The whole constitutive model is presented as well as its calibration. Finally, the validation of the DEM approach is demonstrated through simulations of penetration and perforation tests conducted on concrete targets.