The specimens utilized in the tests were electrochemical etched with a grid of overlapping circles with 2 mm initial diameter d and the method employed for determining the FLC was based upon measuring the in-plane strains (ɛ1, ɛ2) from grid points located along predefined directions crossing the crack perpendicularly. The in-plane strains (ɛ1, ɛ2) at the grid points were obtained from conventional circle grid analysis