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COB26 COMPORTAMENTO À FADIGA DE JUNTAS SOLDADAS DE LIGAS DE ALUMÍNIO / FATIGUE OF ALUMINIUM ALLOY WELDED JOINTS
Alfredo a Silva Ribeiro1, António Augusto Fernandes2
1Secção de Engenharias - Universidade de Trás-os-Montes e Alto Douro/IDMEC. Quinta de Prados 5000 Vila Real
2Faculdade de Engenharia, Rua dos Bragas, 4099 Porto Codex, Portugal- E- mail: aaf@garfield.fe.up.pt
The design of welded joints coupled with the presence of weld defects can impair severely the fatigue resistance of fabrications subjected in service to cyclic loads. Traditionally the design of welded structures has been based on the use of SN curves, defined experimentally, which do not take into account the presence of weld defects. New means of fatigue behaviour prediction are thus needed. For this purpose a comparative analysis of fatigue prediction models, based on analytical and experimental methods, was carried out, taking into account, in particular, the initiation phase. The methodologies proposed by Neuber, Glinka and Heuler were compared.
The models were validated by an experimental programme carried out with welded 6061-T651 aluminium alloy.
Keywords: Fatigue, stress concentration factors, fatigue initiation, fatigue propagation, failure, fatigue cracks.
COB361 ANISOTHERMAL ANALYSIS OF THE DAMAGE LOCALIZATION IN METALLIC BARS SUBMITTED TO CYCLIC LOADINGS
Pedro Manuel Calas Lopes Pacheco
Departamento de Engenharia Mecânica - CEFET/RJ
Av. Maracanã 229, Maracanã - 20271-110, Rio de Janeiro, Brasil - E-mail: calas@cefet-rj.br
Heraldo S. Costa-Mattos
Departamento de Engenharia Mecânica - UFF, Rua Passo da Pátria, 156 - 24210-240, Niterói, Brasil - E-mail: heraldo@caa.uff.br
The present paper presents a mechanical model to study the thermomechanical coupling effects on low cycle fatigue life of metallic materials. The ASTM standard for low cycle fatigue testing establishes that the gradient of temperature during a test must not exceed ± 2 K. For high inelastic amplitudes and/or high frequencies it is recommended the use of cooling devices in order to maintain the specimen temperature in the established range. Experimental curves obtained in such controlled conditions are often used to predict the lifetime of real structures, assuming the hypothesis of isothermal processes. In real problems without cooling devices, such assumption may lead to inadequate predictions if small safety factors are adopted. Simple numerical simulations of 316L stainless steel bars are presented and analysed showing that the hypothesis of isothermal processes may be inadequate when cyclic inelastic deformations are involved. The results show that part of plastic work is transformed into heat, resulting in a temperature rise that affects substantially the mechanical behaviour of the material.
Keywords: Low-Cycle Fatigue, Thermomechanical Coupling, Damage Mechanics, Modelling.
COB390 UMA ANÁLISE DO COMPORTAMENTO À FRATURA DE AÇOS ESTRUTURAIS MICROLIGADOS UTILIZADOS EM APLICAÇÕES ÁRTICAS
Celso P. M. Pereira*, C. Moura Branco** & A. Sousa e Brito**
* Faculdade de Engenharia de Guaratinguetá - FEG/UNESP, CEP 12500-000 Guaratinguetá-SP, Brasil - Fax 012 525 24 66
** Departamento de Engenharia Mecânica, Instituto Superior Técnico - ICEMS/IST
Av. Rovisco Pais, 1 - 1096 Lisboa Codex , Portugal - Fax 01 847 40 45
The fracture toughness behaviour of four microalloyed structural steel, with different composition and process routes was evaluated for artic applications. CTOD three point bend tests were carried out at a range of temperatures between +10ºC and -110ºC in HAZ of submerged arc butt welded specimens. Microstructural analysis and hardness (HV) profiles mensurement were also carried out to complement the mechanical tests. The results show that all the four steels can work at -50ºC and withstand a CTOD value in excess of 0.2 mm .
Keywords: Fracture Toughness, Microalloyed Steels, Weld Microstructures, Welding and HAZ Properties.
COB558 COMPORTAMENTO DOS POROS NO LIMITE DE FADIGA DE ALTO NÚMERO DE CICLOS EM MATRIZ MONOFÁSICA / BEHAVIUOR OF POROUS IN LIMIT ENDURENCE HIGH CICLIC IN THE MICROSTRUCTURE MONOPHASIC
Gabriel Federico Calle Sotelo
Departamento de Engenharia de Materiais, Universidade Estadual de ponta Grossa
Ponta Grossa - Paraná. Rua Nabuco de Araujo s/n Campus Universitário
CEP.: 84031 - 510 Brasil - E mail: gcsotelo@ ufpg.br
Fatigue life curves were get up adopting two criterion: one fracture and other of infinit life. The scattering of results of the same tension the make necessary of analysis statistic. Actually the industry aeronautic and automotive analyse of test fatigue assumed that distribution of logaritmic life is normally. Four groups of diferent size were evaluated with the same porosity. The result showed that porous with small area increase of fatigue limit up 59.9% in comparison with the group higher size porous. There is coalescense of porous without reach of critic size crack
Keywords: Sintered, Fatigue, Fracture, Porosity, Crack, Sinterizado, Fadiga, Fratura, Porosidade, Trinca
COB618 Propriedades mecânicas monotônicas e cíclicas de um aço microligado ao Ti e Nb nas condições como-fornecido e normalizado/Monotonic and cyclic mechanical properties of a titanium and niobium microalloyed steel in as-received and normalized conditions.
Enrico José Giordani, Tácito Brandão Pinto, Peterson Ferrandini, Valdir Alves Guimarães & Itamar Ferreira
Departamento de Engenharia de Materiais, Faculdade de Engenharia Mecânica - UNICAMP
C.P. 6122 - CEP 13.083-970 Campinas, Brasil - E-mail: itamar@fem.unicamp.br
The purpose of this work is to analyze the
monotonic and cyclic mechanical properties of the API 5L X65
steel, a titanium and niobium microalloyed low carbon steel, in
two microstructural conditions: as-received -CF- and normalized
(from 1193 K)-N1-. Tension and low cycle fatigue tests have been
conducted in order to analyze the tension properties [yield
strength (s e), tensile strength (s t), fracture
stress (s f), reduction in area (RA), and strain
hardening exponent (n)] and low cycle fatigue properties [fatigue
strength coefficient and exponent (
and 
), fatigue ductility coefficient and exponent (
and c), and cyclic
strain hardening exponent (n')]. It was observed that the N1
condition showed better behavior, in the range 
, when comparing to the
CF condition. In high cycle fatigue, for low levels of strain,
the CF condition presented better behavior when comparing to the
N1 condition, in spite of the values of 
for these conditions, they are
practically the same and equal to 1075 MPa, due to the big
difference between the fatigue strength exponent: 
for the CF condition and
for the N1
condition. The CF condition presented cyclic softening for all
strain range, and the N1 condition presented cyclic softening for
and cyclic
hardening for 
. The Incremental
step (IS) method was very efficient for obtaining the cyclic
stress-strain curve for the CF condition, when comparing to the
conventional method (by using several specimens). However, for
the N1 condition the results from IS method were not
satisfactory.
Key words: Mechanical properties, Low cycle fatigue, Microalloyed steel. Propriedades mecânicas, Fadiga em baixo ciclo, Aço microligado.
COB933 PROPRIEDADES MECÂNICAS DE FADIGA DE BAIXO E ALTO CICLO DE UM AÇO Cr-Mn-N / LOW AND HIGH CYCLE FATIGUE MECHANICAL PROPERTIES IN A Cr-Mn-N STEEL
Luiz Vicente Vareda1 & Dirceu Spinelli2
1Departamento de Engenharia de Estruturas, Escola de Engenharia de São Carlos-USP. Av. Dr. Carlos Botelho, 1465, CEP 13560-250 - São Carlos - SP. Fax: (016)274-9261.
2Departamento de Engenharia de Materiais, Escola de Engenharia de São Carlos-USP. Fax: (016)274-9213. E-mail: dspinell@sc.usp.br
In the present work, the low and high cycle fatigue mechanical properties in a Cr-Mn-N austenitic stainless steel used for application in drill collars were investigated. The temperature dependence of the tensile properties was determined and it was found that the yield strength, ultimate strength and elongation values decrease significantly with the temperature. The low and high cycle fatigue testing were carried out at room temperature according to ASTM E606 and ASTM E466 standards, with R= -1. At high temperature, the low cycle fatigue properties were estimated from monotonic properties obtained in the tensile testing. The results showed small influence of temperature in the fatigue life in the short-life range and great influence in the long-life range. Near fatigue limit a great scattering of data was observed. The obtained fatigue limit was 452 MPa which represents 47% of the ultimate tensile strenght of material.
Keywords: Low cycle fatigue; high cycle fatigue; austenitic stainless steel / Fadiga de baixo ciclo; fadiga de alto ciclo; aço inoxidável austenítico.
COB940 PROPAGAÇÃO DE TRINCAS DE FADIGA EM JUNTAS SOLDADAS POR SAW NO AÇO C-Mn 516-70N/FATIGUE CRACK PROPAGATION IN WELD JOINTS OF C-Mn 516-70N STEEL
Isabel Cristina Ramos Antunes, Nazareno das Neves & Herman Jacobus Cornelis Voorwald
Departamento de Materiais e Tecnologia, Faculdade de Engenharia - UNESP - Guaratinguetá CEP: 12.500-000 Guaratinguetá - E-mail: voorwald@feg.unesp.br
In this paper the fatigue crack propagation in weld metal, deposited with submerged arc welding on carbon-manganese steel is investigated. Five combinations flux-wire were studied, with fatigue samples subjected to cyclic loading. Experimental and theoretical results were compared using Paris equation, and was also possible to identify the best combination regarding fatigue crack propagation.
Keywords: Fadiga, Aço, C-Mn 516-70N, Propagação de trincas, Equação de Paris/ Fatigue, C-Mn 516-70N steel, crack propagation, Paris equation.
Rodrigo Rossi & Marcelo Krajnc Alves
Departamento de Engenharia Mecânica, UFSC, Trindade, CEP 88010-970 Florianópolis, Brasil, E-mail: Krajnc@grt03.grante.ufsc.br
We present, in this work, a theory and propose an algorithm for the analysis of the damage of low cycle fatigue in mechanical components. A return mapping type of algorithm is used in the integration of the fully coupled elastoplastic and damage equations. The damage theory used in this work, proposed by Lemaitre (1992), is well-founded in the framework of thermodynamics of irreversible process. The model takes into account a non-linear isotropic and kinematic hardening rule. The algorithm proposed for the integration of the set of evolution equations is based on the algorithm presented by Benallal et al (1988) and uses the Newton-Raphson method in order to solve not only the set of local nonlinear equations but also the set of global nonlinear equations. A Galerkin finite element method is employed in the discretisation of the problem where a Quad9 element has been implemented. A two-dimensional plane stress problem, concerning a plate with a hole, is solved with the objective of illustrating the evolution of damage variable.
Keywords: damage, fatigue, low cycle fatigue, material degradation
COB1152 Modelos de Confiabilidade para a Previsão da Vida à Fadiga / MODELS FOR FATIGUE RELIABILITY ANALYSIS
Jorge Luiz de Almeida Ferreira & José Luiz de França Freire
Departamento de Engenharia Mecânica - PUC-Rio, Rua Marquês de São Vicente, 225 - Gávea, Rio de Janeiro, RJ, CEP 22.453-900
The present work describes two analytical models for fatigue reliability analysis. These models are developed under the assumption that cumulative fatigue damage and its critical value follow a lognormal or a Weibull distribution. To verify the predicted results the Monte Carlo analysis was used. From this analysis it was verified that the interference statistical model, based on a lognormal distribution, describes better the behavior of the fatigue’s reliability.
Keywords: acumulação de Dano, confiabilidade / cumulative damage, fatigue reliability.
.