An assessment of different approaches for measuring crack sizes in fatigue and fracture mechanics specimens

Abstract

Several fatigue and fracture mechanics test standards prescribe the use of fatigue precracked specimens, and measured initial and final crack sizes are required for the analyses. All these test methods utilize the X-Point Average Method, with X = 2 ÷ 9, for measuring crack sizes, but another approach, the Area Average Method, is also often used for the same purpose. This investigation compared the two measurement approaches on 140 fracture toughness tests performed on various materials and specimen types, both in the ductile-to-brittle transition (Master Curve) and upper shelf (J-R tests) fracture regimes. Results obtained fully support the inclusion of the Area Average Method in all test standards requiring crack size measurements.