Doutorado em Engenharia Mecânica

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Navegando Doutorado em Engenharia Mecânica por Assunto "Aço inoxidável duplex"

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    Estudo do comportamento mecânico em soldas do aço inoxidável lean duplex UNS S32304 utilizando modelos de encruamento
    (Universidade Federal do Espírito Santo, 2023-01-27) Caetano, Gabriela Aksascki; Orlando, Marcos Tadeu D Azeredo; https://orcid.org/0000000283876504; http://lattes.cnpq.br/3562894103432242; https://orcid.org/0000000333721835; http://lattes.cnpq.br/6385356041873036; Bozzi, Antônio César; https://orcid.org/0000-0003-4857-0216; http://lattes.cnpq.br/3017292130810807; Passos, Carlos Augusto Cardoso; https://orcid.org/0000-0002-6303-3569; http://lattes.cnpq.br/2528679879816545; Mucsi, Cristiano Stefano; https://orcid.org/0000-0002-8637-4999; http://lattes.cnpq.br/2583729137737338; Bezzon, Vinicius Danilo Nonato; http://lattes.cnpq.br/8711723831656721; Vieira, Estefano Aparecido
    Duplex stainless steels are characterized by their weldability, corrosion resistance, and good mechanical properties, the latter two properties being due to their biphasic microstructure of ferrite and austenite. The main focus of this research was to investigate the stress-strain behavior using work hardening models of the lean duplex stainless steel UNS S32304 with a thickness of 1.8 mm, welded by autogenous TIG process followed by heat treatment at different temperatures. In addition, initial investigations were carried out with laser beam welding using powder of duplex steel with TiB2 dispersion as a filler material. Microhardness tests, metallographic characterization with stereoscopy, optical and scanning electron microscopy, tensile test, and phase quantification by image processing were performed to evaluate the specimens welded by autogenous TIG process. The metallographic analysis showed that the heat treatments after TIG welding promoted an increase in the austenite phase content. An analysis of the stress-strain curves using work hardening models showed that the Voce and Hockett-Sherby models presented goodness-of-fit with the experimental data. In addition to the research, it was demonstrated that the parameters of both models are correlated with the volumetric content of austenitic phase in the fusion zone. Furthermore, laser beam welding with powder as filler material showed complete penetration, complete melting of the powder and the sheet, and no porosity was detected. It was verified through instrumented indentation measurements the dispersion of TiB2 and increased hardness and mechanical strength of the weld.
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    Um modelo constitutivo para o comportamento plástico em tração uniaxial de metais baseado na definição do expoente de encruamento instantâneo
    (Universidade Federal do Espírito Santo, 2023-04-03) Gonoring, Tiago Bristt; Orlando, Marcos Tadeu D'Azeredo; https://orcid.org/0000000283876504; http://lattes.cnpq.br/3562894103432242; https://orcid.org/0000-0002-6698-6701; http://lattes.cnpq.br/5654906035884625; Passos, Carlos Augusto Cardoso; https://orcid.org/0000-0002-6303-3569; http://lattes.cnpq.br/2528679879816545; Ferreira, Jetson Lemos; http://lattes.cnpq.br/7279360933683556; Alves, Haimon Diniz Lopes; https://orcid.org/0000-0002-3319-744X; http://lattes.cnpq.br/5728108084133745; Carneiro, Marcelo Bertolete; http://lattes.cnpq.br/5985238373861974; Castro, Nicolau Apoena; Vieira, Estefano Aparecido
    This work has developed a novel proposition for the strain-hardening equation. This proposition had its genesis in the phenomenological definition of the instantaneous strain-hardening exponent. The first part of the work describes a two-step method for the determination of the strain hardening curves, when submitted to high levels of plastic deformation. For this purpose, the plastic behavior of an Ti-stabilized interstitial-free steel sheet (EEP grau 3 – NBR5915-2) was evaluated in two steps. In the first stage, data from the symmetric biaxial expansion test, 'Bulge test', were used in conjunction with Hill's quadratic yield criterion 48 to generate an effective strainhardening curve, or transformed data. In the second step the isotropic hardening laws or hardening equations were fitted to this data. The strain-hardening equation that presented the best fit was the one that combines the Swift-Hockett-Sherby (S-HS) models. The results showed that the better the fit of a strain-hardening equation, the greater the tendency of its strain-hardening curve to describe experimental instantaneous strain-hardening exponent curves. Based on this first part of the work a new constitutive model was developed to describe the stress-strain curve. The constitutive equation is described by the product of two functions of polynomial exponential type. One is dimensionless and is responsible for generating the shape of the strain-hardening curve (true stress-true plastic strain curve), for a given polycrystalline metal alloy and is defined as the normalized strain-hardening function. The second function gives in stress units the points on the curve generated by the normalized hardening function, and furthermore, enables the transformation/shifting of the hardening curve for different stress levels as a function of the boundary conditions. This function is defined as the strain hardening amplitude function. Both functions depend on the determination of the polynomial coefficients generated by fitting an interpolating polynomial to the experimental true stress-true plastic strain data on a natural logarithmic scale, while only the strain hardening amplitude function depends on the values of true uniform elongation and true yield strength. An iterative method is proposed to determine for each metal alloy the amount of polynomial coefficients such that it minimizes the root mean square error (RMSE) between the experimental uniaxial tensile data and the values predicted by the model. These polynomial coefficients are used to predict the instantaneous strain hardening exponent curve. In addition, from the strain hardening equation, it was possible to deduce a strain hardening rate equation, which uses the model predicted stress values and the instantaneous strain hardening coefficient values. The model was validated to describe with excellent accuracy, based on mean square error and coefficient of determination values, the strain hardening behavior from experimental uniaxial tensile data on a duplex 2304 stainless steel alloy. The alloy showed parabolic shaped strain-hardening curves and sigmoidal strain-hardening curves. The new strain hardening model was able to predict the strain hardening behavior of the sigmoidal and parabolic shaped curves of the lean duplex 2304 stainless steel alloy. Additionally, the model was able to describe with very good approximation the experimental curves of the incremental strain-hardening exponent and incremental strain-hardening rate.