| dc.description.abstract | The present thesis address the issue of localization (or discontinuous failure) in quasi-brittle materials modelled as elastic-degrading media, using two dierent regularization strategies, applied individually as well as in a combined form: a regularization at the formulation level with the micropolar continuum theory, and a regularization at the numerical level using smoothed point interpolation meshfree methods. In order to allow the representation of quasi-brittle media with the micropolar continuum model, a unied monodissipative formulation for elastic degradation in micropolar media, dened in terms of secant tensors, loading functions and degradation rules, has been proposed, also deriving a number of scalar damage models within its general scheme. A peculiar compact representation for micropolar media has been introduced, in order to guarantee a formal compatibility between classic and micropolar constitutive models. Taking advantage of this compatibility, the micropolar models have been implemented within an existing object-oriented constitutive models framework originally conceived for classic media, characterized by its independence on the underlying numerical method and analysis model adopted during an analysis. Well-known concepts of acceleration waves propagation, such as the Maxwell compatibility condition and the FresnelHadamard propagation condition, have been derived for the proposed micropolar formulation, in order to obtain a proper localization indicator as a both analytical and numerical tool for the evaluation of the regularization eects induced by the micropolar material parameters. Existent smoothed point interpolation methods, originally developed for classic elasticity and elasto-plasticity, have been extended to the case of elastic degradation in classic media. The peculiar weakened-weak form which they are based on, has been also extended to the micropolar continuum, considering both elasticity and elastic degradation. These methods have been implemented within the same object-oriented project of the micropolar constitutive models framework. A number of simulations regarding problems of numerical and induced localization in damage models, allowed to point out the regularization eects of the micropolar theory in nite element analyses, as well as the regularization eects of smoothed point interpolation methods in classic elastic-degrading models. Both these strategies were capable to individually regularize the behaviour of a number of analyses. Furthermore, their combination allowed to improve the results in the cases where the use of just one of them wasnt sucient. The same results were obtained with another set of simulations performed using two dierent real experimental tests as a basis for the discrete models. In this case, beside the regularization of material instabilities, is was also possible to observe a certain capability of the smoothed point interpolation methods to provide mesh-objective results during the analyses. | |
