Local second gradient models and damage mechanics: 1D post-localisation studies in concrete specimens

Continuum damage mechanics is often used as a framework for describing the variations of the elastic properties of due to micro-structural degradations. Experimentally, concrete specimens exhibit a network of microscopic cracks that nucleate sub-parallel to the axis of loading. Due to the presence of heterogeneities in the material (aggregates surrounded by a cement matrix), tensile transverse strains generate a self-equilibrated stress field orthogonal to the loading direction, a pure mode I (extension) is thus considered to describe the behaviour even in compression. This rupture mode must be reproduced numerically. This is the reason why the failure criterion of the chosen constitutive law is expressed in terms of the principal extensions and that a tension test is modelled at the end of this paper. The influence of micro-cracking due to the external loads is introduced via damage variables, ranging from 0 for the undamaged material to 1 for a completely damaged material