Application of Digital Image Correlation for Estimation of Fatigue Crack Closure Level

The paper is devoted to the estimation of fatigue crack closure levels under a slow loading-unloading cycle for a precracked single side notched specimen. The crack closure level was determined by DIC technique, when optical images were registered with the help of a high-magnification optical microscope. The shape of hysteresis loops is analyzed to estimate their changing with the distance from the crack tip. Furthermore, the crack closure levels for each "load-displacement" curve were computed by the mean area method. The variation of the crack closure levels with their distance from the specimen edge is discussed. The technique used could be applied for automatic noncontact crack closure measurements under fatigue testing with either constant or variable amplitude.