Abstract
This paper presents a semiempirical modification of Irwin's fracture analysis for a semielliptical surface crack in a plate. The plastic zone correction factor is replaced by a term chosen so that the modified Irwin equation predicts fracture at ultimate tensile strength for zero crack depth. The effects of normal experimental error and material property variations are considered, and a statistical procedure for averaging the results of a series of tests is presented. A similar analysis for through-the-thickness cracks is discussed but not evaluated. Surface-crack test data from the literature (for aluminum, magnesium, titanium, and steel alloys and aluminum weldments) are analyzed. The method yields a toughness parameter for each material which relates fracture stress to crack size, generally within about ± 5 per cent . The method appears to be usable when crack size and material thickness are too small to allow a valid fracture mechanics analysis. It is even effective when fracture stresses are above yield. At present the analysis is limited to crack depths less than about half the material thickness. The available data are not sufficient to determine whether the modified toughness parameter is independent of material thickness.
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