Abstract This study is based on the numerical simulation of the mechanical response of yttrium-stabilized zirconia ceramic (3Y-TZP) dental implants as a function of their intrinsic geometry and masticatory loads. Samples (n=20) of 3Y-TZP ceramics were compacted, sintered at 1500 °C - 2h, and characterized by relative density, X-Ray diffraction (XRD), and scanning electron microscopy (SEM). The elastic parameters (modulus of elasticity and Poisson ratio), used in the numerical simulations, were measured by the Impulse Excitation Technique, and the bending strength was obtained using piston-on-three-balls testing. An authorial implant design and, comparatively, commercial implant CAD models were used in this study as an initial geometry of dental implant in a typical adult mandible anatomy. From CAD and CAE techniques, finite element models were generated for all implant geometries. Loading cases were considered based on different intensities (100N to 500N) and orientation angles (45° or 90°) to reproduce the human masticatory efforts. The numerical predictions were compared with finite element simulations of gold-standard titanium-based implants. The investigated 3Y-TZP sintered ceramics presented high densification (> 99%), with a microstructure formed by submicron equiaxed tetragonal zirconia grains. The 3Y-TZP average bending strength obtained from piston-on-three-balls testing is 1192 ± 99 MPa. For both dental implant geometries, the zirconia implants showed average strength of less than 550 MPa, which, in turn, is independent of the masticatory load value or orientation angle. All finite element predictions are 50% inferior to the corresponding measured flexural strength values and preliminarily enable the 3Y-TZP ceramics for dental implant applications without fracture risk.

RESUMO Nos últimos anos, vários estudos foram realizados buscando reduzir o peso de veículos automotores, a fim de diminuir as emissões de poluentes. Neste cenário os aços de baixa densidade do sistema Fe-Mn-Al-C podem ser considerados uma alternativa promissora para suprir essas exigências da indústria automotiva. Geralmente, nos aços de baixa densidade, uma quantidade considerável de alumínio é adicionada a fim de reduzir a densidade geral do aço. No entanto, altos teores de alumínio promovem características distintas na microestrutura, destes aços quando comparados aos aços convencionais, como a presença do carboneto k ((Fe, Mn)3AlC), além da necessidade de se entender a combinação deste elemento com outros elementos de liga que podem ser adicionados. Neste contexto, este trabalho tem como objetivo avaliar a microestrutura, a dureza e a densidade resultantes em função da influência do Al e do Nb em uma nova composição química pertencente ao sistema Fe-Mn-Al-C, na condição trabalhada a quente, a partir de análises de difração de raios X, microscopia eletrônica, medidas de dureza e densidade por princípio de Arquimedes. Os resultados permitiram indicar que o alto teor de Al adicionado promoveu uma redução de cerca de 13% na densidade, em relação aos aços estruturais tradicionais, e a estabilidade da ferrita δ até a temperatura ambiente. A condição avaliada apresentou a temperatura ambiente uma microestrutura formada por uma matriz de ferrita δ e α, juntamente com precipitados de carboneto k (AlFe3C) e carboneto de nióbio (NbC), estes dois últimos devido as adições de Al e Nb, resultando em uma dureza de 59,4 ± 1 HRA e uma estimativa do limite de resistência a tração de próximo a 800 MPa – dentro da faixa dos aços avançados de alta resistência (Advanced High Strenght Steels – AHSS).

ABSTRACT In recent years, several studies have been carried out seeking to reduce the weight of motor vehicles to reduce pollutant emissions. In this scenario, low-density steels from the Fe-Mn-Al-C system can be considered a promising alternative to meet these requirements of the automotive industry. Generally, in low-density steel, a considerable aluminum amount is added in order to reduce the overall density of the steel. However, high aluminum contents promote distinct characteristics in the microstructure of these steels when compared to conventional steels, such as the k carbide presence ((Fe,Mn)3AlC), in addition to the need to understand the combination of this element with other alloying elements that can be added. In this context, this paper aims to evaluate the resulting microstructure, hardness and density as a function of the Al and Nb influence in a new chemical composition belonging to the Fe-Mn-Al-C system, in hot worked condition from X-ray diffraction and eletron microscopy analyses, hardness, and density measurements by Archimedes’ principle. The results indicated that the high added Al promoted a reduction of about 13% in density, in relation to typical structural steels, and the δ ferrite stability up to room temperature. The condition evaluated at room temperature presented a microstructure formed by a matrix with δ and α ferrite, together with k-carbide (AlFe3C) and niobium carbide (NbC) precipitates, the latter two due to the Al and Nb additions, resulting in 59.4 ± 1 HRA hardness and an estimated tensile strength limit close to 800 MPa – within the range of the Advanced High Strength Steels (AHSS).

This work aimed to analyze the damage behavior of cold rolled TRIP780 steel sheet submitted to interrupted uniaxial tensile tests performed along the rolling direction. The formation of voids is investigated as a function of the straining level using digital image analysis of scanning electron micrographs to obtain the measures of void density, void area fraction, void aspect ratio and mean void size. The volume fractions of both ferrite/martensite and retained austenite constituents were obtained from X-ray diffraction measurements. An abruptly decrease of retained austenite was observed at early stages of deformation followed by a slow saturation. The resulting strain-induced martensite is responsible for improving the formability of the TRIP780 as observed by instantaneous strain-hardening exponent. In the lower strain range, growth and coalescence of existing microvoids prevailed at both in-plane directions whereas nucleation of microvoids was also observed along the loading direction. Conversely, nucleation prevailed at the transverse direction in the intermediate strain range whereas growth and coalescence were predominant aligned to the loading direction. At larger strain levels, growth and coalescence of microvoids prevailed at both directions. The microvoids were initially found around inclusions and at the interface of ferrite-martensite phases and lastly also at the ferrite matrix.

In this work, the formability of a hot-dip galvanized interstitial-free (IF) steel sheet was evaluated by means of uniaxial tensile and Forming Limit Curve (FLC) tests. The FLC was defined using the flat-bottomed Marciniak's punch technique, where the strain analysis was made using a digital image correlation software. A plastic localization model was also proposed wherein the governing equations are solved with the help of the Newton's method. The investigated hot-dip galvanized IF steel sheet presented a very good formability level in the deep-drawing range consistent with the measured Lankford values. The predicted limit strains were found to be in good agreement with the experimental data of the hot-dip galvanized IF steel sheet owing to the definition of the localization model geometrical imperfection as a function of the experimental surface roughness evolution and, in particular, to the yield surface flattening near to the plane-strain stress state authorized by the adopted yield criterion.

This paper describes a modeling procedure for tandem cold metal rolling, including the linearization step and system identification for control. The tandem cold rolling process is described by a mathematical model based on algebraic equations developed for control purposes and empirical relations. A state-space model is derived and detailed analyses in open loop are presented, concerning the sensitivity with regard to the variations in process parameters and results for the application of a new subspace identification method are compared with classical methodologies. Therefore, this work intents to be a contribution for developments in new control strategies for tandem cold rolling process that offer the potential to reduce the design efforts, the commissioning time and maintenance in rolling mills. The preliminary results obtained with this model have shown reasonable agreement with operational data presented at literature for industrial cold rolling process.

A Curva Limite de Conformação (CLC) é uma ferramenta muito útil, tanto na avaliação do comportamento plástico de chapas, quanto no projeto do ferramental para solucionar problemas de manufatura nas etapas de tentativas de erros-e-acertos. Esse trabalho apresenta o modelamento matemático da CLC com base em equações constitutivas em elasto-plasticidade e um critério de plasticidade anisotrópica. Demonstra-se, primeiro, que as deformações-limites no domínio de estiramento biaxial são controladas por um parâmetro material definido pela razão entre os limites de escoamento em deformação plana e tração biaxial simétrica. As previsões teóricas do modelo proposto apresentaram boa concordância com medidas experimentais disponíveis, na literatura, para uma chapa de alumínio A1100, e sugerem, igualmente, que os parâmetros do modelo de plasticidade, adotado para descrever anisotropia inicial de chapas metálicas, sejam identificados com bases em ensaios monotônicos de tração uniaxial e biaxial.

The Forming Limit Curve (FLC) is a very useful tool to assess either the plastic behavior of thin metallic sheets or the tooling design to solve manufacturing problems during the try-out steps. This work presents the mathematical modeling of the FLC based on elasto-plastic constitutive equations and anisotropic plasticity yield criterion. It is firstly demonstrated that the limit strains in the biaxial stretching domain are controlled by a material parameter defined by the ratio between the yield stresses in plane-strain tension and equibiaxial tension. The theoretical predictions of the proposed model showed a good agreement with the experimental data available in the literature for an aluminum A1100 sheet and also indicated that the parameters of plasticity model, adopted to describe the initial plastic anisotropy of metallic sheets, must be identified from monotonic uniaxial and biaxial tensile tests data.

In this work the theoretical solutions based upon the upper-bound theorem recently proposed by Pérez and Luri [Mech. Mater. 40 (2008) 617] for the equal channel angular extrusion process (ECAE) are analyzed by performing a 25 central composite factorial analysis. The uniaxial mechanical properties of commercial pure aluminium are considered by assuming isotropic nonlinear work-hardening combined to von Mises and Drucker isotropic yield criteria to predict the ECAE load and the effective plastic strain. From the proposed 25 factorial analysis, the main parameters affecting the ECAE pressure may be ranked as: (1) Friction factor, (2) die channels intersection angle, (3) outer and (4) inner die corners fillet radii and lastly, (5) plunger velocity. Alternatively, the effective plastic strain is mainly controlled by the die channels intersection angle and, in a less extent, by the outer and inner die corners fillet radii.