Influence of the Confined Behaviour and the Tensile Strength of Concrete Slabs Under Projectile-Impact

Abstract

Severe damage modes are observed in concrete structures when subjected to impulse loading as projectile-impact or blast loading. For instance, the impact of a kinetic penetrator generates scabbing on the front face, radial cracking in the whole target and, for high impact velocities or a thin target, spalling on the rear face. These damage mechanisms may strongly decrease the penetration resistance of concrete structures. On the other hand, high confining pressures in front of the projectile may lead to a micro-cracking and collapse of pores in the vicinity of the tunnel. Moreover both confined and tensile behaviours are influenced by humidity level of the concrete. Therefore the numerical modelling of concrete slabs under projectile-impact relies on the use of coupled modelling in which the hydrostatic and deviatoric behaviours of the concrete under high pressure is modelled in addition to the anisotropic damage induced in dynamic tensile loading. In the present work, a series of numerical simulations of impact tests have been conducted considering different humidity levels and target thicknesses. The confined behaviour of the concrete material is modelled through the KST (Krieg-Sweenson-Taylor) plasticity model. The so-called DFH (Denoual-Forquin-Hild) damage model combined with a cohesion model is used to describe the tensile strength and softening behaviour of concrete in tension. A series of computations have been performed to assess the influence of the confined behaviour and tensile strength on the ballistic performance of concrete slabs.