In fracture mechanics studies of ductile materials, it is necessary to measure accurately the near crack tip deformation during crack advance. Assuming an analytical model which links surface displacements with internal stresses near the crack tip[1], useful information about the stress states inside the material may be determined by measuring the surface displacements near the crack tip. Experimental measurements may be correlated to the calculated displacements so that the model for crack advance may be verified. Once this has been completed, the experimental measurements of near crack tip displacements for a given material under different loading and environmental conditions may be input to the model to predict the corresponding internal stresses.