Font Size: 

Fatigue crack propagation rates are affected by the characteristics closeto the crack tip. A method is developed to measure the displacements along the crack,close to the crack tip, using high resolution scanning electron microscope images.Images are taken throughout the load cycles to observe the displacements of a crackexposed to one single overload. The potential drop technique is used to measure theelectrical contact between the crack surfaces.For experiments with R=0.03 and ΔK in the mid Paris region and higher, a remainingdisplacement is detected and both the crack opening and closure loads are decreasedafter the overload. This leads to an increasing effective stress intensity factor rangewhich results in an initially higher crack propagation rate following the overload.