Rationale

A rather popular and alternative method for measuring initial and final crack sizes from the fracture surfaces of fatigue and fracture specimens is the Area Average Method, which measures the surface area enclosed by the crack front, the specimen lateral surfaces (or the side-groove roots for side-grooved specimens), and a reference line corresponding to the origin of crack size measurements. The area is divided by the specimen thickness or net thickness to obtain the crack size. It is herein proposed to add the Area Average Method to E1820 as an alternative to (not as a replacement of) the existing 9 Point Average Method. The item was balloted several times at the E08.07 subcommittee level between 2022 and 2024, receiving several persuasive negatives and comments, which have prompted further changes. The combined main/sub ballot item presented here is the result of multiple in-person and remote discussions, and contains all the changes deriving from those discussions. One of the latest technical items concerned the use of the reduced/deformed specimen (net) thickness within the region of stable crack extension for the calculation of the final crack size in case of lateral contraction of the specimen. The technical justification for the use of the deformed thickness, based on the comparison between final crack sizes measured with the 9-Point Average and Are Average methods on 49 fracture specimens of different configuration and size, is included at the end of this ballot. All proposed changes with respect to the current version of E1820 are marked with “Track Changes”.