Extracting Fracture Parameters Using Local Collocation of Full-field Displacement Data

ull-field analysis of optical data is routinely carried out for extracting crack tip parameters.'-6 Typically, surface or thickness average measurements are analyzed using overdeterministic least-squares procedure with two-dimensional plane stress asymptotic field equations as basis functions. Commonly used linear and nonlinear algorithms in such analyses have been reviewed by Sanford.' Experimental simulations, however, invariably deal with finite size fracture specimens and hence threedimensional deformations dominate the near tip region. Therefore, optical data in the close vicinity of the crack tip needs to be avoided to ensure an accurate determination of the fracture parameter^.^ In some instances, such as in case of a crack lying along an interface, three-dimensional effects .