Experimental characterization and comparison of planar and corrugated aluminum sheets

To evaluate the effect of the corrugation [1] on the mechanical behavior of aluminum plates, a corrugated sheet on aluminum alloy Al1050 is characterized under tensile mechanical tests at room temperature. To characterize anisotropic behavior of the material, tensile experiments are carried out in three different tensile directions i.e. 0, 45 and 90° with respect to the rolling direction. All experiments are performed until final failure using both planar and corrugated sheets for comparison issues. Concerning the experimental supplies, a tensile testing machine is used which can handle forces until 5 kN and can perform monotonic tensile as well as cyclic displacement and force controlled tests. The tensile machine is connected with a digital image correlation background. The measurement apparatus is equipped with two cameras for the detection of displacement fringes. The equipment is able to detect transversal and longitudinal displacements and calculate strain values at also virtual rectangular gauges or along straight lines. The responses of both planar and corrugated plates are compared in the macroscopic level within the force-displacement curves, damage localization zones and macroscopic crack propagation paths. The experimental data for Al1050 is quite interesting because it will be used for the material parameters identification of anisotropic elasto-plastic models combined with mixed hardening and isotropic damage [2]. The implemented models are validated later by comparisons between finite element simulations of Marciniack tests in the FE code Abaqus® and complementary experimental data

2D adaptive FEM simulation of failures in high-speed impacts

The simulation of high-speed impacts needs the use of advanced constitutive equations required for the accurate prediction of the different thermomechanical fields and their mutual interactions (temperature, large strains, hardening, damage, friction …). Since these fields localize inside intense shear bands (ISB), ductile micro-cracks initiate inside these ISB leading to the initiation of macroscopic crack and its fast propagation until the final fracture occurs. Accordingly, these advanced constitutive equations should take into account not only the strong thermomechanical coupling but also the ductile damage and its strong effect (coupling) on the other thermomechanical fields. In this work a complete set of advanced and fully coupled thermo-elasto-viscoplastic-damage constitutive equations accounting for mixed nonlinear isotropic and kinematic hardening fully coupled with the ductile isotropic damage and the thermal softening for time dependent finite plasticity is presented. Related numerical aspects in the framework of a fully adaptive 2D finite element strategy are developed and briefly discussed. This adaptive procedure is applied to the simulation of simple high velocity impact of thick sheets with dynamic ductile fracture occurrence. Attention is paid to the localization of the main thermomechanical fields inside the ISB as well as to the macroscopic cracks initiation and growth under high velocity impact

O letramento crítico e o ensino de inglês no 1º ano do ensino médio da Escola Estadual Quintela Cavalcanti em Arapiraca/Alagoas

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPESEm nosso trabalho, debruçar-nos-emos sobre questões de letramento crítico dentro e fora da escola, e como estes letramentos estão sendo abordados por professores de língua inglesa na atualidade. A pesquisa conta com o suporte teórico de pesquisadores que abordam o tema, como Franco e Tezza (2001), Leavis (1969), Carraher (1999), Monte Mór (2002), as OCEM (2006), Paulo Freire entre outros. O trabalho está dividido em dois momentos, no primeiro momento iremos tratar de uma reflexão sobre o letramento crítico no ensino, entendendo, portanto, como o letramento crítico pode contribuir na formação do ser crítico. Em nosso segundo momento, abordaremos o letramento crítico no ensino de inglês no ensino médio, em escola estadual participante do Programa Institucional de Bolsa de Iniciação à Docência/PIBID no interior de Alagoas. Através de leituras iniciais do aporte teórico utilizado neste trabalho, percebemos que em pleno século XXI, em muitas escolas, as aulas de línguas não abordam o letramento crítico, tornando-se então motivo de reflexão, uma vez que o letramento deve ser entendido como um processo de construção do conhecimento crítico que leve o aluno a usar esse conhecimento em suas práticas sociais.São Cristóvão, S

An elasto-plastic self-consistent model for damaged polycrystalline materials: Theoretical formulation and numerical implementation

Elasto-plastic multiscale approaches are known to be suitable to model the mechanical behavior of metallic materials during forming processes. These approaches are classically adopted to explicitly link relevant microstructural effects to the macroscopic behavior. This paper presents a finite strain elastoplastic self-consistent model for damaged polycrystalline aggregates and its implementation into ABAQUS/Standard finite element (FE) code. Material degradation is modeled by the introduction of a scalar damage variable at each crystallographic slip system for each individual grain. The single crystal plastic flow is described by both the classical and a regularized version of the Schmid criterion. To integrate the single crystal constitutive equations, two new numerical algorithms are developed (one for each plastic flow rule). Then, the proposed single crystal modeling is embedded into the self-consistent scheme to predict the mechanical behavior of elasto-plastic polycrystalline aggregates in the finite strain range. This strategy is implemented into ABAQUS/Standard FE code through a user-defined material (UMAT) subroutine. Special attention is paid to the satisfaction of the incremental objectivity and the efficiency of the convergence of the global resolution scheme, related to the computation of the consistent tangent modulus. The capability of the new constitutive modeling to capture the interaction between the damage evolution and the microstructural properties is highlighted through several simulations at both single crystal and polycrystalline scales. It appears from the numerical tests that the use of the classical Schmid criterion leads to a poor numerical convergence of the self-consistent scheme (due to the abrupt changes in the activity of the slip systems), which sometimes causes the computations to be prematurely stopped. By contrast, the use of the regularized version of the Schmid law allows a better convergence of the self-consistent approach, but induces an important increase in the computation time devoted to the integration of the single crystal constitutive equations (because of the high value of the power-law exponent used to regularize the Schmid yield function). To avoid these difficulties, a numerical strategy is built to combine the benefits of the two approaches: the classical Schmid criterion is used to integrate the single crystal constitutive equations, while its regularized version is used to compute the microscopic tangent modulus required for solving the self-consistent equations. The robustness and the accuracy of this novel numerical strategy are particularly analyzed through several numerical simulations (prediction of the mechanical behavior of polycrystalline aggregates and simulation of a circular cup-drawing forming process)

Preface

An advanced numerical methodology is developed for metal forming simulation based on thermodynamically-consistent nonlocal constitutive equations accounting for various fully coupled mechanical phenomena under finite strain in the framework of micromorphic continua. The numerical implementation into ABAQUS/Explicit is made for 2D quadrangular elements thanks to the VUEL users’ subroutine. Simple examples with presence of a damaged area are made in order to show the ability of the proposed methodology to describe the independence of the solution from the space discretization