Crack length and stable crack extension measurements from images acquired by means of a conventional flatbed scanner

摘要

The crack length measurements of both the original crack length and the stable crack extension are requested by several fracture toughness test methods, wherein which high accuracy measurement instruments are demanded. Low magnification optical microscopes as well as travelling-stage microscopes are used to achieve the accuracy requirements, although many times these time-consuming techniques present some experimental difficulties, especially when a great number of specimens have to be measured. A methodology to measure crack length from high-resolution images acquired by means of a desktop flatbed-scanner is presented in this paper. The acquired images are analysed by means of software that allows obtaining the crack length. Several aspects were studied to demonstrate the suitability of the method: the optical resolution, the depth of field and the effects of possible optical aberrations. Finally, an uncertainty balance was performed to demonstrate that the methodology is able to reach the necessary accuracy required by the fracture toughness test methods.