Experimental determination and empirical representation of out-of-plane displacements in a cracked elastic plate loaded in mode I

A Michelson interferometer is applied to a mode I fracture mechanic problem to investigate the out-of-plane displacement near the crack tip. For an elastic cracked plate, it appears that the two-dimensional theory predicts correctly the free-stress surface displacement only in a region greater than half the specimen thickness. Combining this two-dimensional solution and the measurements provided by the interferometer, the out-of-plane displacement is likewise accessible inside the previous region where the state of stress is three-dimensional. A mathematical formulation, using an exponential integral function is then proposed to describe the out-of-plane surface displacement in the measurement area around the crack tip.