Monitoring the fatigue crack growth behavior of composite joints using in situ 2D-digital image correlation

To predict lifetime and damage tolerance of adhesively bonded joints, crack growth behavior need to be understood, as it oftentimes serves as a basis or proof of, e.g., numerical models. Within this work, a method is presented to measure crack length in dynamically loaded adhesively bonded CFRP-joints by means of 2D digital image correlation. Automated picture acquisition at the maximum force level within a cycle allows measurements during the fatigue testing. The strain level in front of the crack tip was defined as maximum possible strain within the bond line. Higher strains were denoted as crack. Marking the crack path automatically led to the associated crack length and could afterward be derived to a crack propagation rate. Different destructive tests were carried out on composite single, double and crack lap shear specimens.