São Bernardo do Campo, Brazil
São Bernardo do Campo, Brazil

Time filter

Source Type

Dos Santos D.C.,Praca Marechal Eduardo Gomes | Magnabosco R.,Ignatian Educational Foundation FEI | De Moura-Neto C.,Aeronautics Institute of Technology ITA DCTA
Corrosion | Year: 2013

The main purpose of this contribution was the study of the relation between sigma formation and pitting corrosion resistance of a UNS S31803 duplex stainless steel aged at 850°C. Solution-treated samples were isothermally aged at 850°C for up to 360 h. The corrosion resistance of aged UNS S31803 steel was analyzed through cyclic potentiodynamic polarization tests in 0.6 M sodium chloride (NaCl) solution. The main mechanism of sigma phase formation was nucleation and growth from ferrite, in agreement to the Johnson-Mehl-Avrami- Kolmogorov kinetics model. This model suggests a change on the mechanisms of sigma phase formation from nucleation and growth from ferrite to the growth from austenite. Pitting morphology was related to the material microstructure. The pitting growth mechanism occurred by selective corrosion of the chromium-depleted areas of the specimens. Both pitting and repassivation potentials decreased with an increase of sigma volume fraction. Recovery of the corrosion resistance was observed in the early stages of sigma formation, probably related to chromium redistribution to depleted areas. © 2013, NACE International.


Liberto R.C.N.,Villares Metals S.A. | Magnabosco R.,Ignatian Educational Foundation FEI | Alonso-Falleiros N.,University of Sao Paulo
Corrosion Science | Year: 2011

This work studied the electrochemical behavior of a solution treated or 550°C aged Cu10Ni-3Al-1.3Fe alloy, in 0.01M NaCl aqueous solution, through potentiodynamic polarization in both stagnant condition or under erosion process. Results showed the occurrence of a passivity break potential (Epb), related to the beginning of the denickelification process, which occurred as a localized attack under stagnant electrolyte. Under erosion conditions localized denickelification was not observed, despite of the presence of Epb. This could indicate that selective corrosion of Ni, which caused the observed Epb, occurred as a dissolution-redeposition process, with removal of the Cu deposits during erosion process. © 2011 Elsevier Ltd.


De Melo E.B.,Brazilian Technological Institute of Aeronautics | Magnabosco R.,Ignatian Educational Foundation FEI | De Moura Neto C.,Brazilian Technological Institute of Aeronautics
Materials Research | Year: 2013

This work evaluates the phase transformations during aging of an UNS S31803 DSS at 650°C and its influence on the DOS. The material was solution treated at 1175°C and then aged at 650°C for times up to 360 h. SEM-BSC images indicate the formation of Cr2N, σ and ÷ phases in the samples aged at 650°C. The analysis of DL-EPR curves, obtained in a 1 M H2SO4 + 0.25 M NaCl + 0.01 M KSCN solution, shows an increase in DOS values for samples aged at 650°C. Probably, this increase observed in DOS values is mainly related to the presence of Cr-and/or Mo-depleted á, as a result of σ phase, ÷ phase and/or Cr2N formation at 650°C. Moreover, a possible healing up of Cr-and/ or Mo-depleted areas is observed between 1 h and 4 h of aging at 650°C.


Donato G.H.B.,Ignatian Educational Foundation FEI | Moreira F.C.,Ignatian Educational Foundation FEI
ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) | Year: 2014

Fracture toughness and Fatigue Crack Growth (FCG) experimental data represent the basis for accurate designs and integrity assessments of components containing crack-like defects. Considering ductile and high toughness structural materials, crack growing curves (e.g. J-R curves) and FCG data (in terms of da/dN vs. AK or A J) assumed paramount relevance since characterize, respectively, ductile fracture and cyclic crack growth conditions. In common, these two types of mechanical properties severely depend on real-time and precise crack size estimations during laboratory testing. Optical, electric potential drop or (most commonly) elastic unloading compliance (C) techniques can be employed. In the latter method, crack size estimation derives from C using a dimensionless parameter (μ) which incorporates specimen's thickness (B), elasticity (E) and compliance itself. Plane stress and plane strain solutions for μ are available in several standards regarding C(T), SE(B) and M(T) specimens, among others. Current challenges include: i) real specimens are in neither plane stress nor plane strain - modulus vary between E (plane stress) and E/(1-v2) (plane strain), revealing effects of thickness and 3-D configurations; ii) furthermore, side-grooves affect specimen's stiffness, leading to an "effective thickness". Previous results from current authors revealed deviations larger than 10% in crack size estimations following existing practices, especially for shallow cracks and side-grooved samples. In addition, compliance solutions for the emerging clamped SE(T) specimens are not yet standardized. As a step in this direction, this work investigates 3-D, thickness and side-groove effects on compliance solutions applicable to C(T), SE(B) and clamped SE(T) specimens. Refined 3-D elastic FE-models provide Load-CMOD evolutions. The analysis matrix includes crack depths between a/W=0.1 and a/W=0.7 and varying thicknesses (W/B = 4, W/B = 2 and W/B = 1). Side-grooves of 5%, 10% and 20% are also considered. The results include compliance solutions incorporating all aforementioned effects to provide accurate crack size estimation during laboratory fracture and FCG testing. All proposals revealed reduced deviations if compared to existing solutions. Copyright © 2014 by ASME.


dos Santos D.C.,Ignatian Educational Foundation FEI | Magnabosco R.,Ignatian Educational Foundation FEI
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2016

This work presents an improved kinetic study of sigma phase formation during isothermal aging between 973 K and 1223 K (700 °C and 950 °C), based on Kolmogorov-Johnson-Mehl-Avrami (K-J-M-A) model, established from volume fraction of sigma phase determined in backscattered electron images over polished surfaces of aged samples. The kinetic study shows a change in the main mechanism of sigma formation between 973 K and 1173 K (700 °C and 900 °C), from a nucleation-governed stage to a diffusion-controlled growth-coarsening stage, confirmed by a double inclination in K-J-M-A plots and microstructural observations. A single inclination in K-J-M-A plots was observed for the 1223 K (950 °C) aging temperature, showing that kinetic behavior in this temperature is only related to diffusion-controlled growth of sigma phase. The estimated activation energies for the nucleation of sigma phase are close to the molybdenum diffusion in ferrite, probably the controlling mechanism of sigma phase nucleation. The proposed time-temperature-transformation (TTT) diagram shows a “double c curve” configuration, probably associated to the presence of chi-phase formed between 973 K and 1073 K (700 °C and 800 °C), which acts as heterogeneous nuclei for sigma phase formation in low aging temperatures. © 2016, The Minerals, Metals & Materials Society and ASM International.


Donato G.H.B.,Ignatian Educational Foundation FEI | Cavalcante F.G.,Ignatian Educational Foundation FEI
American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP | Year: 2015

High responsibility components operating under cyclic loading can have their resistance against initiation and growth of fatigue cracks highly influenced by previous thermomechanical processing. Within the interest of the present work, different manufacturing processes and installation techniques incorporate cold plastic straining to engineering structures; two typical examples on the oil and gas fields are: i) the offshore pipelines installation method called reeling; ii) the fabrication of pipes using the UOE method and pressure vessels through calendering. Within this scenario, this work investigates the effects of plastic prestrain on the fatigue crack growth rates (da/dN vs. ΔK) of a hot-rolled ASTM A36 steel. Different from previous results from the literature, in which prestrains were applied directly to machined samples, in this work uniform prestraining was imposed to steel strips (1/2" thick) and specimens were then extracted to avoid (or minimize) residual stress effects. Prestrain levels were around 4, 8 and 14% and C(T) specimens were machined from original and prestrained materials according to ASTM E647 standard. Fatigue crack growth tests were carried out under load control in an MTS 810 (250 kN) equipment using R = 0.1. Results revealed that plastic prestraining considerably reduced crack growth rates for the studied material, which was expected based on the literature and hardening behavior of the studied material. However, results also revealed two interesting trends: i) the larger is the imposed prestrain, the greater is the growth rate reduction in a nonlinear asymptotic relationship; ii) the larger is imposed ΔK, the more pronounced is the effect of prestraining. Crack closure effects were also investigated, but revealed no influence on the obtained mechanical properties. Consequently, results could be critically discussed based on effective crack driving forces and elastic-plastic mechanical properties, in special those related to flow and hardening. The conclusions and success of the employed methods encourage further efforts to incorporate plastic prestrain effects on structural integrity assessments. Copyright © 2015 by ASME.


Donato G.H.B.,Ignatian Educational Foundation FEI | Bianchi M.,Ignatian Educational Foundation FEI
Procedia Engineering | Year: 2011

Classical plasticity theories and yield criteria for ductile materials, such as Tresca and von Mises original formulations predict that yielding is independent on the hydrostatic stress state (pressure), which means that tensile and compressive stress-strain behaviours are considered equal and are equally treated. This approach is reasonable for ductile metallic materials but sometimes inaccurate for polymers, which commonly present larger compressive yield strength, therefore being characterized as uneven. Polymer unevenness can be of great interest for mechanical structural design since components that present regions operating under compression can be optimized taking this phenomenon into account. Compressive stress-strain data for polymers are very scarce in the literature, and as a step in this direction this work presents three key-activities: i) four selected polymers were tested under tension and compression to identify unevenness and assess its levels; ii) pressure dependent yield criteria applicable for polymers were briefly reviewed; iii) experimental results were incorporated in adapted design practices using modified yield criteria implemented in optimization and finite element computations. Results show that taking unevenness into account and implementing modified criteria in the numerical techniques for structural calculation can provide mass reductions up to ∼ 38% even with simple geometric changes, while keeping original safety and stiffness levels. © 2011 Published by Elsevier Ltd.


Moreira F.C.,Ignatian Educational Foundation FEI | Donato G.H.B.,Ignatian Educational Foundation FEI
American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP | Year: 2010

Experimental evaluation of geometry-dependent material's fracture resistance using constraint-designed SE(T) specimens has proved to be an accurate option to assess the structural integrity of pipelines and pressure vessels reducing excessive conservatism. In this context, this work presents procedures for experimental J-integral and CTOD (δ) evaluation using the eta (η) method applied to tension clamped SE(T) specimens made of homogeneous materials and also containing mismatched joints. Initially, the conceptual background is presented, followed by the description of the refined non-linear finite element models developed, which provide the necessary evolution of load with increased load-line displacement and crack mouth opening displacement. As results, are presented a variety of η factors for J -integral and CTOD calculations, which are not available in current standardized procedures. The main objective is to allow fracture resistance experimental evaluation using specimens of different a/W-ratios, material flow properties, weld joint configurations and levels of weld strength mismatch. The main motivation is the possibility of enhancing accuracy of pressure vessels and piping integrity assessments, since these later present very close fracture conditions if compared to SE(T) specimens. The present results, when taken together with previous developments, extend the knowledge about the use of clamped SE(T) specimens. The reader should enhance the studies about the topic with the complimentary paper with the same title beginning but involving pin-loaded SE(T) specimens. Copyright © 2010 by ASME.


Donato G.H.B.,Ignatian Educational Foundation FEI | Moreira F.C.,Ignatian Educational Foundation FEI
American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP | Year: 2013

Engineering procedures for design and integrity assessment of structural components containing crack-like defects are highly dependent on accurate fracture toughness and Fatigue Crack Growth (FCG) experimental data. Considering ductile and high toughness structural materials, crack growing curves (e.g. J-R curves) and FCG data (in terms of da/dN vs. ΔK or ΔJ) assumed paramount relevance. In common, these two types of mechanical properties severely depend on real-time and precise crack size estimations during laboratory testing. Optical measurement, electric potential drop or (most commonly) elastic unloading compliance (C) techniques can be employed. In the latter method, crack size estimation derives from C using a dimensionless parameter (μ) which incorporates specimen's thickness (B), elasticity (E) and compliance itself. Plane stress and plane strain solutions for μ are available in several standards regarding C(T), SE(B) and M(T) specimens, among others. Current challenges include: i) real specimens are in neither plane stress nor plane strain - modulus vary between E (plane stress) and E/(1-ν2) (plane strain); ii) furthermore, side-grooves affect specimen's stiffness, leading to an "effective thickness". Results from Shen et al. and from current authors revealed deviations larger than 10% in crack size estimations following existing practices, especially for shallow cracks and side-grooved samples. In addition, compliance solutions for the emerging SE(T) specimens are not yet standardized. As a step in this direction, this work investigates 3-D and side-groove effects on compliance solutions applicable to C(T), SE(B) and clamped SE(T) specimens. Refined 3-D elastic FE-models provide Load-CMOD evolutions. The analysis matrix includes crack depths between a/W=0.1 and a/W=0.7 on 1/2T, 1T and 2T geometries. The 1T geometry is taken as the reference and presents width to thickness ratio W/B = 2. Side-grooves of 5%, 10% and 20% are considered. The results include compliance solutions incorporating 3D and side-groove effects to provide accurate crack size estimation during laboratory fracture and FCG testing. The proposals were verified against current standardized solutions and deviations were strongly reduced. Copyright © 2013 by ASME.


Donato G.H.B.,Ignatian Educational Foundation FEI | Ganharul G.K.Q.,Ignatian Educational Foundation FEI
American Society of Mechanical Engineers, Pressure Vessels and Piping Division (Publication) PVP | Year: 2013

Simulations and structural integrity evaluations including severe plasticity have undergone significant expansion during recent years (e.g. fracture mechanics FE models including ductile tearing and/or generalized yielding), which demand accurate true stress-strain data until fracture. This is a consequence of the use of high toughness ductile materials subjected to severe loadings and high levels of operational efficiency and optimization. However, tensile tests present one inconvenience when providing such data, since the occurrence of plastic instability (necking) complicates the direct assessment of true stress-strain curves until final fracture. Two main difficulties can be pointed out: i) the nonuniform geometry assumed by the cross sections along its length and; ii) the imposition of a complex triaxial stress state. The first occurrence can only be overcome by real-time physical measurements. The second occurrence demands a correction model to provide an equivalent stress including triaxial effects. Current authors recently demonstrated that even the well-known Bridgman's correction presents limitations, particularly for strains greater than ∼ 0.50 - 0.60, which motivated proposals to better describe the geometrical evolution of necking minimizing the need for real-time physical measurements [1]. As a new step in this direction, this work presents three key contributions: i) first, experiments regarding the geometrical evolution of necking were largely extended incorporating 10 materials to corroborate the validity of the recently proposed model (including Carbon, stainless steels and copper); ii) second, and for the same materials, the necking region was investigated in more details to verify to which extent an osculating circle well describes the high deformation region. A new model could be proposed to better support future solid mechanics analyses regarding equilibrium and stress/strain fields; iii) finally, a modified Bridgman's model is proposed, followed by recommended practices for testing. The results provide further support to σ-ε assessment considering severe plasticity and demanding less physical measurements. Copyright © 2013 by ASME.

Loading Ignatian Educational Foundation FEI collaborators
Loading Ignatian Educational Foundation FEI collaborators