Compaction and tensile damage of concrete in impacts problems on concrete structures F. Gatuingt, L. Daudeville and G. Pijaudier-Cabot, M. ASCE LMT-Cachan, ENS Cachan / CNRS / Université P. et M. Curie, Cachan, F 94235, France Fabrice.Gatuingt@lmt.ens-cachan.fr Abstract: The objective of this study is to develop a model for concrete with an emphasis on tension and compaction. The non-linear response of the material in tension is captured with a coupled elastic- damage model. The non-linear response of the material in compaction is modelled with the help of a coupled plasticity – damage approach. The final model is based on mechanics of porous materials, damage and plasticity. In order to show the influence of compaction, simulations of split Hopkinson test performed on confined concrete and on a concrete rod submitted to an impact have been carried out. These simulations demonstrate the importance of compaction, which has a tendency of strengthening the concrete structure. Introduction In a concrete structure subjected to a shock or to an impact, for instance a concrete slab, the material is subjected to various states of stresses, which yield different failure modes. Near the striker, severe hydrostatic compression is observed. This state of stress produces irreversible compaction of the material. Farther from the impact location, the confinement stresses decrease and the material experiences compression with a moderate triaxial state of stress. Finally, compressive wave reflection may occur and can result in a tensile wave, which will interact with compressive waves and will produce scabbing, i.e. tensile cracking induced by wave interaction. Computational analysis of concrete and reinforced concrete elements subjected to this type of loading history requires the implementation of a constitutive relation capable of capturing the major features of the material response under such loads. The originality of the model presented here, compared to the approaches based on cap models in plasticity, is the description of the variations of the material elastic stiffness. The degradation of the elastic moduli is described in the model by two damage scalars: a tension damage variable and a compression's one. Tension damage is controlled by the positive elastic strains (Mazars 1984). In order to capture the evolution of irreversible strain we use a modified Gurson’s yield function with associated flow rules (Gurson 1977, Needleman and Tvergaard 1984). The evolution of the volume fraction of voids entering in the Gurson’s yield function is directly related to compression damage. When it decreases, it produces an increase of the material stiffness and therefore a decrease of material damage. Hence, the evolutions of compression damage and plastic strain are entirely coupled. Finally, computations on test cases, which exhibit the major properties and characteristics of the model, are presented. We do not intend to deal here with thorough comparisons with experimental results, but rather to exhibit the influence of the major characteristics of the proposed model on the response of small structures in transient dynamics.