CHARACTERIZATION OF MODE-I STRESS INTENSITY FACTORS BY THE SHADOW OPTICAL METHOD

In this study the shadow optical method is applied to characterize the stress-strain field in the vicinity of the tip of a crack in an aluminium alloy. Two specific areas are investigated. Firstly, the range of validity of the plane stress region near the crack tip is assessed by the variation in the reference distance, and a parameter, including the initial radius for a given specimen thickness, is characterized. Secondly, the relationship between the plane stress region and specimen thickness very close to the crack tip is investigated, and it is shown that plane stress conditions prevail at distances from the crack tip greater than two thirds of the thinnest specimen and one fifth of the thickest specimen analysed. These measurements underline the essential information that can be obtained about the state of stress in the crack tip region equal to the radius of the initial curve where the singular K field dominates. Hence, this paper addresses the extent of the validity of the asymptotic stress field, subject to mode-I-loaded crack tips.