1,721,097 research outputs found
Multiscale damage contact-friction model for periodic masonry walls
No full textIn the present paper, a multiscale analysis of periodic masonry walls is developed. In particular, a micromechanical
analysis is presented for the unit cell, introducing nonlinear constitutive laws, based on damage
and friction models, for the mortar and for the blocks. In order to deduce the overall response of
regular masonry arrangements to be used for the multiscale analysis, the Transformation Field Analysis
(TFA) homogenization procedure is extended to the case of nonuniform eigenstrain. A multiscale procedure
is proposed implementing the nonlinear homogenization technique at Gauss point level, in 2D plane
state finite element. A nonlocal integral model is adopted in order to overcome problems due to the localization
of strain and damage. Numerical examples of homogenization are carried out, comparing the nonlinear
mechanical response of the masonry, obtained by adopting the proposed homogenization
technique, with the results recovered by evolutive nonlinear finite element analyses. Moreover, numerical
applications regarding the mechanical response of masonry structures are performed in order to validate
the efficiency of the multiscale approach. In particular, a comparison with experimental data,
available in literature, is presented
Computational homogenization of 3D printed materials by a reduced order model
No full textThe aim of this paper is to study the effective mechanical behavior of 3D printed materials. To this purpose a micromechanical study is developed in order to investigate the influence of the heterogeneity of the 3D printed material at the microscale on the overall response. A reduced order model, usually adopted for the analysis of heterogeneous materials, is extended to model the response of the printed material, considered as periodic. In particular, the Mixed Transformation Field Analysis (MxTFA), based on a mixed-stress variational formulation of the elasto-plastic theory, considering the inelastic strain based on a representation of the self-equilibrated stresses, is developed. A unit cell, representative of the 3D printed material's microstructure, comprising a fiber and interstitial voids is defined and divided in subsets. In each subset, a self-equilibrated stress is considered introducing a constant, linear, or quadratic approximation and the plastic multiplier is assumed constant. Some numerical applications are developed considering different unit cells and different loading conditions. The obtained results are compared with some experimental results, available in literature, and with results obtained from non-linear finite element analyses. The application of a TFA-based method to the 3D printed materials could provide an effective tool for the prediction of the mechanical behavior with a significant reduction of the history variables defining the evolution problem
Multiscale technique for the analysis of 3D-printed materials
No full textThe mechanical behaviour of structural elements made of 3D-printed materials is numerically investigated. With this aim a multiscale approach that allows to determine the macroscopic response, as depending on the material heterogeneity at the microscale level, is conceived. A non-linear laminate finite element that employs a reduced homogenization technique at each integration Gauss point is developed. In detail, the Piecewise Uniform Transformation Field Analysis is implemented. In order to validate the procedure, some numerical applications are developed. The obtained results are compared with evidence of experimental tensile and bending tests, available in literature. The application of a multiscale strategy, employing a reduced order method at the Gauss point level for the analysis of 3D-printed structural elements, could represent a good compromise in terms of accuracy of the results and computational efficiency
Computational homogenization of composites experiencing plasticity, cracking and debonding phenomena
No full textAim of the present paper is the development of a homogenization technique able to determine the overall mechanical response
of composite materials taking into account the cracking and plastic behavior of its constituents and the decohesion process among
them. A representative volume element of a composite material is studied. The plastic effects in the constituents are considered
introducing a plastic model with isotropic and kinematic hardening. The debonding between constituents and the cracking process
are described introducing a cohesive damage interface model that takes into account also the unilateral contact and frictional
effects. In particular, a new procedure based on the nonuniform Transformation Field Analysis is presented. The plastic strains in
the constituents and the inelastic relative displacements along the interfaces are approximated as linear combinations of inelastic
scalar modes that are functions of the spatial variables. The coefficients of the linear combinations are the internal variables of the
problem that are computed solving the evolutive problem. Some numerical applications are carried out to verify the efficiency of the
proposed homogenization approach in reproducing the overall mechanical response of composites characterized by cracking and
plastic phenomena in the constituents and debonding between them. The homogenization results are compared with the solution
obtained by micro-mechanical nonlinear finite element analyses
VEM-based tracking algorithm for cohesive/frictional 2D fracture
No full textThe present paper proposes an innovative nucleation and propagation algorithm for fracture evolution in 2D cohesive media, based on virtual element method (VEM) technology. Initially, an interface cohesive law is described, which is able to account for the crack opening due to the evolution of a damage variable in mode I, mode II, and in mixed mode; the model includes unilateral contact and frictional effects. The VEM, which is used to model the elastic behavior of the bulk material, is presented in a simple and viable way, illustrating the projection operation necessary for defining strain and stress in a typical element, and discussing the stabilization technique. Then, the numerical algorithm for reproducing the crack nucleation, the fracture path generation and evolution is described. The procedure fundamentally consists in two steps, i.e. the nucleation and propagation criteria, and the topological adaptive mesh refinement. Numerical applications are developed in order to assess the ability of the proposed procedure to satisfactorily reproduce the crack nucleation and growth in solids. Comparisons with numerical results available in literature are reported, remarking the reliability of the implemented algorithm
High-order virtual element method for the homogenization of long fiber nonlinear composites
No full textA high-order virtual element method (VEM) for homogenization of long fiber reinforced composites is presented. In particular, periodic composites are considered studying square or rectangular unit cell arrays and circular inclusions. A suitable displacement representation form is adopted reducing the three-dimensional problem to an equivalent two-dimensional one. Material nonlinearity is taken into account for the matrix which can be plastic or visco-plastic. The formulation is proposed for linear and high-order virtual elements. Numerical applications are performed to assess the accuracy of the VEM formulation in comparison with the classical finite element approach. In particular, convergence investigations on the overall elastic moduli and on the Mises equivalent stress are performed. Elasto-plastic and visco-plastic analyses are carried out exploiting the local mesh refinement features typical of VEM showing efficiency of polygonal discretizations
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