This communication addresses the localization properties of a coupled damageplasticity formulation for concrete materials to provide informations on the onset of material bifurcation and the critical failure modes. Two separate loading functions are considered, one for damage and one for plasticity. A three-invariant yield surface is used to model plasticity and to consider the significant role of the intermediate principal stress and the Lode parameter on the failure of concrete materials. A non-associated flow rule is employed to control inelastic dilatancy. To model degradation of the elastic stiffness a scalar-valued isotropic damage formulation is introduced based on the total strain energy formulation is used. Monotonic and cyclic uniaxial compression experiments are performed on concrete cylinders under displacement control and photogrammetric images are collected for Digital Image Correlation Analysis. The triaxial based
This paper revisits the stress concentration problem in the proximity of circular perforations of different diameters and presents results of an experimental program on flat bars made of high strength steel, mild steel, cast iron and aluminum alloys. A digital image correlation (DIC) system is used to monitor the experiments and provide displacement and strain fields on the surface of the specimens at different stages of axial loading. The extended finite element method (XFEM) is introduced and applied to the inelastic deformation regime by coupling localization analysis and XFEM to discretely follow crack propagation into the ductile response regime.
In the field of experimental solid mechanics, conventional strain measurement devices such as LVDT and strain gauges provide mean values of strains and displacements at selected locations and gauge lengths; this result is inadequate for the evaluation of a non homogeneous material behaviour. Consequently, during the last decades various full-field non-contact measurement techniques have been proposed for the material characterization and have become more and more popular in the experimental mechanics community. In this work, the Digital Image Correlation (DIC) non-interferometric technique has been used to monitor experiments on aluminum flat bars and to measure displacement distribution on the surface of the specimen for further evaluation and calculation of strains.The results obtained by a Digital Image Correlation System are assessed and the error associated with the post processing of the experimental field data, obtained through the use of the Aramis software, is evaluated and analyzed with the aid of a least square approximation code. This code uses a finite element approximation of the displacement field in order to cover all the target points. A least square approximation of these data is performed and the best nodal displacement values are determined. Based on the nodal data, infinitesimal and finite strain distributions are determined over the surface image window of the specimen. It is observed that this post processing technique provides better results near perforations and edges that are not sensitive to the density of the captured displacement data.
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