Abstract
Abstract. A continuum damage mechanics model has been derived within the framework of irreversible thermodynamics with internal variables in order to describe the behaviour of quasi-brittle materials under various loading paths. The anisotropic character induced by the progressive material degradation is explicitly taken into account, and the Helmholtz free energy is a scalar function of the basic invariants of the second order strain and damage tensors. The elastic response varies depending on the closed or open configuration of defects. The constitutive laws derived within the framework of irreversible thermodynamics theory display a dissymmetry as well as unilateral effects under tensile and compressive loading conditions. This approach verifies continuity and uniqueness of the potential energy. An application to uniaxial tension-compression loading shows a good adequacy with experimental results when available, and realistic evolutions for computed stresses and strains otherwise.
Highlights
Most geomaterials and concrete are regarded as isotropic and heterogeneous materials before any mechanical loading at mesoscopic scale
The application of a mechanical loading causes occurence of defects whose directions of propagation depends on the local stress field, Microcracks propagate in a direction normal to tension, but tend to close in the case of compression with possible frictional slip on the lips of discontinuities
Future work concerns the investigation of the predictive capacities of the anisotropic damage model with unilateral effects, by confronting Finite Element simulations with available experimental results, including conventional triaxial tests and real case studies
Summary
Most geomaterials and concrete are regarded as isotropic and heterogeneous materials before any mechanical loading at mesoscopic scale. Complete crack closure causes a recovery of the material stiffness in the direction of compressive stress, this phenomenon is called unilateral effect (Ramtani et al, 1992; Yazdani and Schreyer, 1988; Torrenti and Djebri, 1990; Krajcinovic, 1989). Under a simple mechanical test one observes that cancelation of loading leads to more or less important irreversible strains (Ortiz, 1985). These effects are caused by frictions at crack closure. More realistic damage model requires a tensorial formulation for a system of defects strongly influenced by the local field of stress.
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