Effect of overload on crack closure in thick and thin specimens via digital image correlation

• Evolution of closure in thick and thin CT specimens prior and after overload.
• Closure quantified through COD and full-field K-Muskhelishvili approaches.
• Closure is distant dependent in retardation zone for thick but not thin CT specimens.
• Full-field K-Muskhelishvili less sensitive to measure closure load than COD.
• Fatigue crack growth plastic zone model fit to experimental data.

The displacement field of compact tension (CT) specimens have been mapped by digital image correlation (DIC) local to growing fatigue cracks to study overload effects for plane stress and plane strain. We have extracted crack opening displacement (ΔCOD) and stress intensity (K) determined by a Muskhelishvili fit to the crack tip displacement field to infer the closure load. In both cases a classical knee was observed upon unloading consistent with closure which disappeared during the accelerated growth following OL, before increasing during retardation. In both cases following OL the crack growth rate is perturbed for a distance similar to the plastic zone.