Abstract

Innovative experimental procedures were developed to study the growth and closure behaviour of small corner cracks. These procedures include: (a) specimen preparation - employing a pre-crack specimen where a crack is grown in cyclic compression, to produce a final specimen with two shallow corner cracks; (b) compliance measurement — placing an active gauge on the mouth of the crack and subtracting the response of a dedicated far-field gauge to obtain a signal dependent on the crack; (c) opening load determination — fitting a curvilinear relation to the differential compliance curve to determine the opening load. The pre-cracking technique and final specimen fabrication minimize residual damage and stresses ahead of the crack tip, on its subsequent fatigue development. The size of the crack is monitored using a thin-film replica technique. The shape of the initial crack front is marked by heat coloration of the fatigue tension (FT) specimen prior to fatigue loading. The closure and growth behaviour of the small corner cracks in the FT specimens is observed in terms of shape and size.

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