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Fatigue crack propagation and cyclic deformation at a crack tip

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Abstract

The fatigue crack propagation relation da/dN = f(R)ΔK2 can be derived with three assumptions: small scale yielding, material homogeneity and that crack tip stresses and strains are not strongly affected by plate thickness. f(R) is a constant at a given stress ratio, R. The effects of plate thickness and stress ratio on crack tip deformation and fatigue crack growth in 2024-T351 aluminum alloy were studied. High ΔK level in a thin specimen causes crack tip necking. Necking is more pronounced at high stress ratio. Necking causes high maximum strain near a crack tip, εmax, and fast crack growth rate. In order to avoid the effects of crack tip necking, plates thicker than 2.5 (ΔK/σY(c))2 should be used.

Résumé

La relation de propagation des fissures de fatigue peut être obtenue à partir de trois hypothèses: déformations plastiques de faible étendue, homogénéité du matériau, et relative indifférence à l'épaisseur de la tole des contraintes et déformations à la pointe de la fissure, f(R) est une constante à rapport des contraintes R fixé.

On a étudié les effets de l'épaisseur de la tole et du rapport des contraintes sur la déformation à l'extrémité de la fissure et sur la propagation de la fissure de fatigue, dans le cas de l'alliage d'aluminium 2024-T351. On constate que des valeurs élevées de ΔK appliquées à des échantillons minces produisent une striction aux extrémités de la fissure. Cette striction est plus prononcée aux valeurs élevées de R, et produit une déformation maximum εmax élevée au voisinage de la pointe de la fissure, ainsi qu'une vitesse de propagation élevée.

Pour éviter les effets perturbateurs de la striction aux extrémités d'une fissure, il conviendrait d'utiliser des éprouvettes dont l'épaisseur soit plus forte que 2,5 (ΔK/σY(c))2.

Zusammenfassung

Die Gleichung da/dN = f(R)ΔK2 für Müdigkeitsrißausdehnung kann mittels drei Hypothesen zugestellt werden: kleine plastische Verformungen, Homogenität des Materials, und daß die Spannungen und Verformungen an der Rißspitze nicht stark von der Plattendicke beeinflußt werden. f(R) ist eine Konstante für ein gegebenes Spannungs-verhältnis R. Man untersucht den Einfluß der Plattendicke und des Spannungsverhältnisses auf die Verformungen der Spitze des Risses und der Müdigkeitsrißausdehnung in einer Aluminiumlegierung 2024-T351. Ein hoher ΔK Wert in einer dünnen Probe führt zu Striktion an der Rißspitze. Die Striktion ist stärker für hohe Spannungsverhältnisse. Die Striktion verursacht eine große Höchstspannung E max in der Nähe einer Rißspitze und einen schnellen Rißwachstumsgrad. Zur Vermeidung der Einflüsse der Rißspitzestriktion soll man Platten benutzen die dicker sind als 2,5 (ΔK/σY(c))2.

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Authors and Affiliations

  1. Department of Chemical Engineering and Materials Science, Syracuse University, 13210, Syracuse, New York, U.S.A.

    Tai Shan Kang & H. W. Liu

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  1. Tai Shan Kang
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Kang, T.S., Liu, H.W. Fatigue crack propagation and cyclic deformation at a crack tip. Int J Fract 10, 201–222 (1974). https://doi.org/10.1007/BF00113926

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  • DOI: https://doi.org/10.1007/BF00113926

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