Deformation Measurements at the Sub-Micron Size Scale: 11. Refinements in the Algorithm for Digital Image Correlation

Improvements are proposed in the application of the Digital Image Correlation method, a technique that compares digital images of a specimen surface before and after deformation to deduce its surface (2-D) displacement field and strains. These refinements, tested on translations and rigid body rotations were significant with regard to the com-puter efficiency and convergence properties of the method. The necessity of using the framework of large deformation theory to accurately compute large rigid body rotation is demonstrated. In addition, the formulation of the algorithm was extended so as to compute the three-dimensional surface displacement field from Scanning Tunneling Mi-croscope topographies of a deforming specimen. The resolution of this new displacement measuring method at the nanometer scale was assessed on translation and uniaxial tensile tests and was found to be 4.8 n m for in-plane displacement components and 1.5 n m for the out-of-plane one spanning a 10 x 10 p m area