Light clusters and the pasta phase

The effects of including light clusters in nuclear matter at low densities are investigated within four different parametrizations of relativistic models at finite temperature. Both homogeneous and inhomogeneous matter (pasta phase) are described for neutral nuclear matter with fixed proton fractions. We discuss the effect of the density dependence of the symmetry energy, the temperature and the proton fraction on the non-homogeneous matter forming the inner crust of proto-neutron stars. It is shown that the number of nucleons in the clusters, the cluster proton fraction and the sizes of the Wigner Seitz cell and of the cluster are very sensitive to the density dependence of the symmetry energy.Comment: 14 pages, 14 figures; Accepted for publication in Phys. Rev.

DD3MAT: a code for yield criteria anisotropy parameters identification

This work presents the main strategies and algorithms adopted in the DD3MAT in-house code, specifically developed for identifying the anisotropy parameters. The algorithm adopted is based on the minimization of an error function, using a downhill simplex method. The set of experimental values can consider yield stresses and r - values obtained from in-plane tension, for different angles with the rolling direction (RD), yield stress and r - value obtained for biaxial stress state, and yield stresses from shear tests performed also for different angles to RD. All these values can be defined for a specific value of plastic work. Moreover, it can also include the yield stresses obtained from in-plane compression tests. The anisotropy parameters are identified for an AA2090-T3 aluminium alloy, highlighting the importance of the user intervention to improve the numerical fit.The authors gratefully acknowledge the financial support of the Portuguese Foundation for Science and Technology (FCT) via the projects PTDC/EME-TME/118420/2010 and UID/EMS/00285/2013. The first author is also grateful to the FCT for the PhD grant SFRH/BD/98545/2013.info:eu-repo/semantics/publishedVersio

Apicultura e bovinocultura de corte: comparativo econômico da implantação hipotética dessas atividades no Pantanal.

Esta publicação foi realizada na forma de um comparativo econômico hipotético entre duas atividades econômicas que podem ser desenvolvidas, simultaneamente ou não, nas propriedades da região pantaneira: a apicultura (alternativa) e a bovinocultura de corte (tradicional). Dessa forma, buscou-se que os parâmetros, produtivos e econômicos de ambas as atividades, considerados nos cálculos fossem os mais realistas possíveis para as condições de uma propriedade (fazenda São Luiz), localizada no Pantanal do Abobral, que foi dedicada tradicionalmente à bovinocultura de corte e na qual o proprietário futuramente pretende instalar a apicultura. Portanto, os critérios e parâmetros avaliados neste comparativo econômico podem contribuir para a tomada de decisões de outros produtores rurais que pretendem desenvolver essas duas atividadesprodutivas em outras propriedades pantaneiras.bitstream/CPAP/56603/1/DOC84.pdfFormato Documento Eletrônico

Modeling of tension–compression asymmetry and orthotropy on metallic materials: numerical implementation and validation

The details concerning the implementation of the yield criterion developed by Cazacu et al. 2006 (CPB06), which accounts for both tension–compression asymmetry and orthotropy of the plastic flow, in the fully implicit FE solver DD3IMP (contraction of ‘Deep Drawing 3-D IMPlicit') are presented in this work. The implemented constitutive model is extensively described, including the analytical first and second order derivatives required to the stress update algorithm. A set of anisotropy parameters describing the mechanical behavior of two metallic materials at room temperature, namely Zirconium and AZ31-Mg alloy, are identified with the DD3MAT (contraction for ‘Deep Drawing 3-D MATerial’) in-house code (Alves, 2004) [2]. The anisotropy parameters are identified for both the CPB06 and the Cazacu and Barlat (2001) (CB2001) yield criteria, in order to emphasize the importance and role of the strength differential effect. The results clearly show that the CPB06 yield criterion is able to accurately describe both the in-plane anisotropy and tension–compression asymmetry, as well a different anisotropic behavior in uniaxial tension and uniaxial compression. The numerical simulation of a four-point bending test is performed, considering different orientations of the beam, i.e. of the hard/soft to deform direction relatively to the load direction, allowing to validate the implementation. The results obtained with the CPB06 show its ability to describe with accuracy the strain fields in the beam's central cross-section, the distribution of the tensile and compressive layers and, consequently, the shift of the neutral layer. The comparison with the results obtained with CB2001 indicates that the strength differential effect affects the final deformed shape of the beam, particularly for materials exhibiting strong tension–compression asymmetry.The authors gratefully acknowledge the financial support of the Portuguese Foundation for Science and Technology (FCT), Portugal via the projects PTDC/EME-TME/118420/2010, UID/EMS/00285/2013 and by FEDER, Portugal funds through the program COMPETE - Programa Operational Factores de Competitividade, under the project CENTRO-07-0224-FEDER-002001 (MT4MOBI). The first author is also grateful to the FCT for the Ph.D. Grant SFRH/BD/98545/2013.info:eu-repo/semantics/publishedVersio

Study of the frictional contact conditions in the hole expansion test

The adoption of advanced high-strength steels is growing in the automotive industry due to their good strength-to-weight ratio. However, the frictional contact conditions differ from the ones arising in mild steels due to the high values of contact pressure. The objective of this study is the detailed numerical analysis of the frictional contact conditions in the hole expansion test. The Coulomb friction law is adopted in the finite element model, using different values for the (constant) friction coefficient, as well as a pressure dependent friction coefficient. The increase of the friction coefficient leads to an increase of the punch force and a slight decrease of the hole expansion. The results show that increasing the friction coefficient postpones the onset of necking, but the localization does not change.Fundação para a Ciência e a Tecnologia(SFRH/BPD/101334/2014

Study on the influence of orthotropy and tension–compression asymmetry of metal sheets in springback and formability predictions

Most yield criteria possess a point-symmetry with respect to its center, meaning that a stress state and its reverse state have the same absolute value. However, this can be an unrealistic approximation, even for cubic metals (both face-centered cubic and body center cubic)), which can present a small asymmetry between the yield stress in tension and compression, i.e. a strength differential (SD) effect. This work analyzes the influence of taking or not into account the SD effect in the modeling of the sheet orthotropic behavior in the numerical simulation of a cylindrical cup drawing process. The yield criterion adopted is the CPB06 [1], including its version with two linear transformations [2], allowing a better fitting of the experimental data available. The material analyzed presents a quite small tension-compression ratio of 0.963. However, this small SD effect leads to a slightly higher punch force during the bending dominated stage, resulting in a very small influence on the springback prediction. The influence on the thickness evolution during the process is negligible.Fundação para a Ciência e a Tecnologia(SFRH/BPD/101334/2014