Study of different DIC approaches to measure crack opening/closing levels in a biaxial crack growth trial with combined HCF/LCF loads

Crack closing forces are important to determine effective cyclic stress intensity factors ∆𝐾𝑒𝑓𝑓 in fatigue crack growth trials. By digital image correlation (DIC), the change of stiffness between the open and closed crack can be measured in different ways evaluating stress-strain curves either globally using integral strain perpendicular to crack growth direction or locally measured by virtual extensometers distributed along the crack. Crack opening and crack closing forces obtained by compliance of integral strain and of crack opening profiles measured by virtual extensometers are compared for a biaxial crack growth trial applying HCF and LCF cycles.