Title

AVALIAÇÃO DA EFICÁCIA DO FECHAMENTO E DO PARÂMETRO K* NA MODELAGEM DE PROPAGAÇÃO DE TRINCAS POR FADIGA EM MATERIAIS ESTRUTURAIS DE INTERESSE AERONÁUTICO

EVALUATION OF THE CRACK CLOSURE AND K* APPROACHES FOR FATIGUE CRACK GROWTH DESCRIPTION ON TWO AERONAUTICAL STRUCTURAL MATERIALS

Authorship

Adib, Anthony M.L.; Baptista, Carlos A.R.P.; Torres, Marcelo A.S.; Souza, Renato C.

Adib, Anthony M.L.

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Baptista, Carlos A.R.P.

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Torres, Marcelo A.S.

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Souza, Renato C.

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DOI

10.5151/2594-5327-0243

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Abstract

Partindo dos vários enfoques que buscam uma expressão genérica para a propagação de trincas por fadiga, este trabalho avalia dois modelos conceitualmente diferentes, porém com mesmo objetivo: descrever os efeitos da razão de tensões na taxa das trincas. O conhecido modelo de Elber, que emprega o conceito de fechamento da trinca ao definir o valor de

From among the various approaches adopted in search of a general fatigue crack growth expression, two distinct concepts are evaluated in the present work: the crack closure model introduced by Elber and the K* parameter recently proposed by Kujawski. Both of them are aimed to describe the so- called R-effects that affect the crack growth rate when asymmetric loadings are applied, and the latter one is an adaptation of the well-known Walker’s model. Two structural materials were chosen for this work: Aluminum alloy Al 2524 T3 and commercially pure titanium (ASTM grade 2). Although morphologically distinct, these materials show very similar mechanical properties. The former was developed during the 1990s to replace its predecessor Al 2024 in fuselage panels; whereas grade 2 titanium is used in aircraft engine bleed ducts and other parts where high strength-to weight ratio and corrosion resistance are needed. The fatigue crack growth tests were conducted under load control and 6 different values of R ratio for each material: 0.05, 0.1, 0.15, 0.30, 0.50 and 0.60. Closure measurements were made using the linear-quadratic method. The performances of the employed methods for crack growth description were compared in terms of the normalized sum of residuals. It is shown that the Kujawski method provides a slightly better description of the crack growth curves.

Keywords

Fadiga; Propagação de trinca; Fechamento de trinca; Carregamentos assimétricos.

Fatigue; Crack propagation; Crack closure; Asymmetric loadings.