Automated Fatigue Crack Growth Monitoring: Comparison of Different Crack-Following Techniques

Ranganathan, N.; Guilbon, G; Jendoubi, K.; Nadeau, André; Petit, J.

doi:10.1520/stp24014s

Cited by 2 publications

(3 citation statements)

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“…The present study, in which four different equivalent constant amplitude concepts were studied for the case of crack propagation under block loadings, permits us to present the following conclusions: lo08 N. RANOANATHAN AND J. R. DESFOROES (1) The root mean squared method leads to reasonably good life estimations only when the number of cycles per block is relatively high, in this case approximately 100 cycles.…”

Section: Discussionmentioning

confidence: 67%

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Equivalent Constant Amplitude Concepts Examined Under Fatigue Crack Propagation by Block Loading

Ranganathan

Desforges

1996

Fatigue Fract Eng Mat Struct

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Abstrad-Fatigue crack growth behaviour under block loading sequences has been studied on the aluminium alloy 2024 T351, using four different equivalent constant amplitude concepts. The root mean squared method gives acceptable results only for relatively long blocks. The equivalent method based on the Pans law (modified to take into account crack closure) gives good predictions for the observed growth rates as does Elbers' method. Finally, a new method based on energy considerations gives excellent results for the studied test conditions. NOMENCLATURE a = crack length BL = block loading da/dN =crack growth rate i = cycle number ECA =equivalent constant amplitude K = stress intensity factor KO = stress intensity factor at crack opening Kmus = maximum stress intensity factor in a block K,, K-= maximum and minimum K levels in a cycle m, rn' = slopes of Pans' law and Elbers' relation respectively N = number of cycles P = load Nq = number of equivalent cycles P , , = maximum load in a block P , , Pd =maximum and minimum loads at cycle i P = crack opening load B = effective mean level Q = energy dissipated per cycle Qi =energy dissipated at cycle i in a block Q,-, = enclosed energy RMS = root mean squared R = load ratio %p = equivalent R ratio R, = load ratio corresponding to cycle i in a block LIE = Elbers' efficiency factor VA = variable amplitude a = specimen compliance AK = stress intensity factor range Qm, = total energy dissipated per block AKem = effective AK 6 =crack mouth opening displacement 998 N. RANGANATHAN AND J. R. DESFORGES

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Section: Discussionmentioning

confidence: 67%

“…lo08 N. RANOANATHAN AND J. R. DESFOROES (1) The root mean squared method leads to reasonably good life estimations only when the number of cycles per block is relatively high, in this case approximately 100 cycles.…”

mentioning

confidence: 99%

Equivalent Constant Amplitude Concepts Examined Under Fatigue Crack Propagation by Block Loading

Ranganathan

Desforges

1996

Fatigue Fract Eng Mat Struct

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“…apply load P and specimen deflection δ for CT specimens. (Ranganathan et al, 1989) In order to calculate the crack length a, first was calculated the compliance C as the slope of the δ-P diagram, as shows Figure 40. In the case of a straight line it's a trivial calculation as happened in the present research but if the relation is another curve, the slope had to be calculated fitting a polynomial relation δ-P and deriving when force corresponds to P average.…”

Section: Measuring Crack Size By Codmentioning

confidence: 99%

Fatigue crack propagation in AA 7050-T7451 alloy considering environment, stress ratio, rolling direction and waveform effects

Barbosa¹,

Fernando²

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AcknowledgmentI'm so graceful with a lot of people who helped me to realize this work, mainly my Mum María Lily Barbosa and in general my family and friends in Colombia and Brazil who makes me believe in selfless friendship. I have a big debt with them and God for giving me as much love.Quero fazer um reconhecimento especial de gratidão ao Brasil e suas faces para mim como o Professor Waldek Wladimir Bosé Filho, o Departamento De Engenharia de materiais mesmo, a EMBRAER pelo fornecimento do material e a CNPq pela bolsa de estudos.Este trabajo es particularmente dedicado a mi Mamá María Lily Barbosa.Un beso enorme para todos los que me dieron la mano en los muchos momentos difíciles de este camino, por que como dijo Cerati si algo está enfermo, está con vida. Gracias de aquellas.....Totales RESUMO BARBOSA, J. F. C. Propagação de trinca por fadiga na liga AA7050-T7451 considerando o efeito do meio ambiente, razão de tensões, direção de laminação e forma de onda.. Dissertação (Mestrado) -Escola de Engenharia de São Carlos, Universidade de São Paulo, São Carlos, 2017.Os principais fatores modificadores extrínsecos e intrínsecos da taxa de propagação de trincas na liga AA7050-T7451 foram avaliados para fornecer subsídios para projetistas de estruturas aeronáuticas, com base na filosofía de tolerância ao dano. A metodologia experimental consistiu em ensaiar corpos de prova do tipo compact tension (CT) da liga nas direções de laminação TL e LT, para verificar seu comportamento sob diferentes razões de tensões, forma de onda e condição ambiente. Os valores de razão de tensão estudados foram 0,1 e 0,5, as formas de onda foram senoidal e trapezoidal ou de Dwell, em condições normais de laboratório, ao ar, e névoa salina 3,5% NaCl, em massa, para simular um ambiente marinho. No caso dos ensaios Dwell, os resultados foram conferidos pelo método de queda de potencial eléctrico (QPE), além do método de flexibilidade elástica.Usando os coeficientes de Walker calculados a partir dos resultados obtidos, pôde-se projetar com precisão o comportamento da propagação de trinca na região de Paris e prever a vida em fadiga usando os diagramas da/dN e S-N para diferentes valores da razão de tensões. O ambiente corrosivo aumenta tanto a taxa de propagação de trinca, quanto o valor de ΔKth por causa da formação de óxidos na trajetória da trinca, que geram um efeito de fechamento sobre a mesma. Quanto à forma de onda, verificou-se que o carregamento Dwell diminui a taxa de propagação de trinca, diminuindo a inclinação das curvas log (da/dN) versus log (ΔK) na região de Paris, ao invés de deslocá-la paralelamente como ocorre com ligas de titânio. A mudança da direção de laminação de LT para TL aumenta a taxa de propagação de trinca por fadiga (PTF) tanto na região de threshold, quanto na região de Paris, onde a mudança de taxa é pequena.Palavras-chave: -Propagação de trinca por fadiga (PTF), determinação da taxa de propagação de trinca, técnicas de medição de trinca, método de queda de potencial elétrico (QPE), corrosão por fadiga, carregame...

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Automated Fatigue Crack Growth Monitoring: Comparison of Different Crack-Following Techniques

Cited by 2 publications

References 7 publications

Equivalent Constant Amplitude Concepts Examined Under Fatigue Crack Propagation by Block Loading

Equivalent Constant Amplitude Concepts Examined Under Fatigue Crack Propagation by Block Loading

Fatigue crack propagation in AA 7050-T7451 alloy considering environment, stress ratio, rolling direction and waveform effects

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