Prediction of fatigue crack initiation lives at elongated notch roots using short crack concepts

Castro, Jaime Tupiassú Pinho de; Meggiolaro, Marco Antônio; Miranda, Antônio Carlos de; Wu, Hao; Imad, A.; Benseddiq, Noureddine

doi:10.1016/j.ijfatigue.2011.10.010

Cited by 37 publications

(37 citation statements)

References 13 publications

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“…Therefore, even experimental K t values, measured as usual at the notched component free surfaces, may underestimate the actual value of max at such notch tips, so 3D effects on stress/strain fields along notch tips may indeed be relevant for some practical applications. Maximum stress and/or strain points indicate preferred locations for crack initiation along the notch front, whereas the stress gradients ahead of such critical points affect how short cracks propagates from them [17][18][19]. If cracks prefer to start at maxima stress or strain points, as reasonably assumed in most damage models, they should do so at the center of thinner notched plates (z/B  0) and closer to the free surfaces (z/B  0.5) of the thicker ones, but the growth of such initially small surface cracks is strongly dependent on the stress gradient around the notch tip, as discussed elsewhere [14].…”

Section: D Effects On Stress Fields Around Notch Tipsmentioning

confidence: 99%

3D thickness effects around notch and crack tip stress/strain fields

Goes¹,

Castro

Meggiolaro

2015

Frattura Ed Integrità Strutturale

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ABSTRACT. Notches and cracks are usually approximately modeled as two-dimensional problems using solutions from plane elasticity to quantify localized stress/strain concentration effects around their tips. However, they may be associated with high gradients that can severely restrict local Poisson-induced transversal strains and cause important 3D stress fields around those tips. Fatigue crack initiation and growth, plastic zone sizes and shapes, and localized constraint effects that affect toughness are typical problems associated with such 3D effects, which may lead to non-conservative damage and life predictions if neglected. To quantify how important they can be, first finite element techniques are used to simulate thickness and notch-tip radius effects in the fields around such tips, and to evaluate their importance from the structural design point of view. Then, versatile sub-modeling techniques are used to study similar effects along the fronts of short and long cracks, and a stepwise re-meshing routine is used to show how an initially straight crack must slightly curve its front during its propagation by fatigue, due to the unavoidable 3D effects that always surround real crack tips.

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Section: D Effects On Stress Fields Around Notch Tipsmentioning

confidence: 99%

3D thickness effects around notch and crack tip stress/strain fields

Goes¹,

Castro

Meggiolaro

2015

Frattura Ed Integrità Strutturale

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“…Its main advantage is to recognize cracks and their effects on the fatigue limit, modeling the actual fatigue limit more realistically because there are no defect-free materials in practice. The pioneer model based on this methodology was proposed by El Haddad, Toper and Smith (ETS) 4, and it has been recently extended to consider notch effects [7][8][9] in the so-called Stress Gradient (SG) model briefly described in Section 1.2.…”

Section: Introductionmentioning

confidence: 99%

Previsão Do Limite De Fadiga De Peças Entalhadas Pelo Modelo Do Gradiente De Tensão E Pela Teoria Da Distância Crítica

Guamán¹,

Castro²

2017

Anais Do Congresso Anual Da ABM

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ResumoO modelo do Gradiente de Tensão (SG) e a Teoria da Distância Crítica (TCD) são usados para estimar o limite de fadiga de corpos de prova com entalhes alongados, e essas estimativas são testadas em C(T) modificados submetidos a tensões cíclicas de amplitude constante com uma razão de tensão R = 0.1. Os valores medidos são comparados com as previsões feitas por ambos os modelos. As previsões do modelo SG estiveram mais de acordo com os resultados experimentais. Também foi demonstrado que o modelo SG é quase equivalente à TCD no caso de entalhes com raios grandes, quando a TCD usa o método do ponto. Para o caso de entalhes afiados, os valores dos limites de fadiga previstos pela TCD são mais conservativos que os previstos pelo modelo SG. Palavras-chave: Limite de fadiga; Modelo do gradiente de tensões (GT); Teoria da distância crítica (TCD). FATIGUE LIMIT PREDICTION FOR ELONGATED NOTCHED SPECIMENS USING THE STRESS GRADIENT MODEL AND THE CRITICAL DISTANCE THEORY AbstractThe Stress Gradient (SG) model and the Theory of the Critical Distance (TCD) are used to estimate the fatigue limit of elongated notched specimens, and such estimates are tested in modified C(T) specimens loaded under constant amplitude cyclic stresses and a stress ratio R=0.1. The measured values are compared with those predicted by both models. The SG model predictions agreed better with the experimental results. It is also demonstrated that the SG model and the TCD using the point method are almost equivalent for blunt notches, whereas for sharp notches the fatigue limit values predicted by TCD model are more conservative than those predicted by the SG model.

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“…Consequently, q-values can also be analytically modeled by studying the behavior of those short fatigue cracks. In particular, the model proposed in [5][6][7] estimates q-values for fatigue loading conditions using sound mechanical principles and well-defined mechanical properties, without the need for any additional data-fitting parameter. Moreover, it allows the notch sensitivity concept to be extended to environmentally-assisted cracking (EAC) problems as well, and its predictions have been validated under liquid metal embrittlement conditions by testing notched Al samples in a Ga environment [8], as well as under hydrogen embrittlement conditions by testing similar steel samples in aqueous H 2 S environments [9].…”

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confidence: 99%

On short cracks that depart from elastoplastic notch tips

Machado¹,

Castro²,

Meggiolaro³

2017

Frattura Ed Integrità Strutturale

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ABSTRACT. The behavior of short cracks that depart from elastoplastic notch tips is modeled to estimate the stresses required to initiate and to propagate cracks in notched structural components, and to evaluate the size of tolerable crack-like defects under general loading conditions. This analysis can model both fatigue and environmentally assisted cracking problems; can evaluate notch sensitivity in both cases; and can as well be used to establish design or acceptance criteria for tolerable non-propagating crack-like defects in such cases. The growth of short cracks is assumed driven by the applied stresses and by the stress gradient ahead the notch tip, and supported by the material resistances to crack initiation and to long crack propagation by fatigue or EAC. In the elastoplastic case, the stress gradient ahead of the notch tip is quantified by a J-field to consider the short crack behavior. The tolerable short crack predictions made by this model are evaluated by suitable fatigue and EAC tests of notched specimens specially designed to start nonpropagating cracks from the notch tips, both under elastic and elastoplastic conditions. KEYWORDS. Short cracks; notch sensitivity; fatigue cracking; environmentally assisted cracking; elastoplastic behavior; J-integral.Citation: Machado, V.M., Castro, J.T.P., Meggiolaro, M.A., On short cracks that depart from elastoplastic notch tips, Frattura ed Integrità Strutturale, 41 (2017) 236-244.

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Prediction of fatigue crack initiation lives at elongated notch roots using short crack concepts

Cited by 37 publications

References 13 publications

3D thickness effects around notch and crack tip stress/strain fields

3D thickness effects around notch and crack tip stress/strain fields

Previsão Do Limite De Fadiga De Peças Entalhadas Pelo Modelo Do Gradiente De Tensão E Pela Teoria Da Distância Crítica

On short cracks that depart from elastoplastic notch tips

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