Improved Fractographic Strength Estimates Based on Surface Profilometry

Abstract

Fractography is a valuable method that uses post-mortem topographical information to estimate the stress field near the fracture origin and help establish the root cause of failures. Typically, in glass and ceramics the mirror radius is one of the features sought for by fractographers since its length could be empirically related to the sample’s strength. The mirror radius is usually subjectively estimated by fractographers though microscopy measurements. Nonetheless, variations in the estimates introduced by inconsistent viewing modes and the subjectivity of observers could lead to substantial errors even when standard protocols such as ASTM C1678 were followed. In this manuscript, a novel method combining a fracture mechanics model describing the mist formation in silicate glasses with profilometry data carried out by confocal laser scanning microscope is introduced. The new method was shown to be able to objectively establish the mirror-mist boundary. Furthermore, it was found that the proposed technique was repeatable within 2% regardless of the magnification or imaging mode used. Whereas the average strength estimated per ASTM C1678 by eight individual observers was influenced by both the magnification and the imaging mode used and displayed standard deviation of over 3%.