Crack closure measurements using Moiré interferometry with photoresist gratings

This paper describes the use of an in situ Moiré interferometer which enables crack closure readings to be taken at any point in the life of a fatigue specimen without the need to transfer the specimen from the loading machine to a separate rig. Measurements of crack closure using this method are presented at a number of different R-ratios, showing the crack peeling open and closed. The experimental results are compared to an analytical model of fatigue crack closure based on the Dugdale strip yield concept, and excellent correlation is achieved.