Abstract
Fatigue crack growth rate, da/dN, of two high strength steels were examined in a laboratory air at different stress ratios, covering almost the entire range of stress intensity, ΔK, from nearly threshold value, ΔKth, to final fracture. The fatigue fracture toughness, ΔKfc, corresponding to the final fracture in fatigue, was also determined. The lower the ΔKfc, the higher da/dN and reduced ΔKth are revealed.
This correlation was analyzed quantitatively based on the four parameter Weibull function. And the stress ratio dependency of the fatigue crack propagation curve can be cleared in a successful manner.
The fatigue characteristic stress intensities, Ke and Kv, are proposed to define the transition behaviour in fatigue crack growth curve, from so called region 1 to 2, and from region 2 to 3, respectively. Especially the Kv valua can be specified to be the 0.63Kfc.
Résumé
On a étudié la vitesse de propagation de fissure en fatigue da/dN de deux aciers à haute résistance dans un atmosphère de laboratoire sous des sollicitations couvrant toute la gamme des intensités de contraintes variables ΔK, depuis une valeur voisine de la valeur du seuil ΔKth jusqu'à celle correspondant à rupture finale.
La ténacité à la rupture par fatigue ΔKfe correspondant à la rupture finale par fatigue a été également déterminée. II s'avère que plus ΔKfe est faible, plus élevée est da/dN et plus ΔKth est réduite. Cette correlation est analysée quantitativement en se basant sur la fonction de Weibull à quatre paramètres. On peut ainsi clarifier la manière dont le rapport de contraintes influe les courbes de propagation des fissures de fatigue.
On propose de définir pas les facteurs caractéristiques d'intensité de contrainte Ke et Kv les comportements de transition de la courbe de vitesse de propagation de la fissure entre respectivement les régions dénommées 1 et 2, et 2 et 3.
En particulier, on peut spécifier que la valeur Kv vaut 0,63 Kfe.
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Sawaki, Y., Tada, S., Hashimoto, S. et al. Fatigue fracture toughness and crack propagation rate. Int J Fract 35, 125–137 (1987). https://doi.org/10.1007/BF00019795
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DOI: https://doi.org/10.1007/BF00019795