Fiber Bridging and Displacement Ratio Effects on Mode I Fatigue Crack Growth in Composite–Metal Adhesive Joints: A Similitude‐Based Study

ABSTRACT This study investigates the Mode I fatigue crack growth and threshold behavior in bimaterial composite/aluminum adhesive joints under displacement ratios: 0.14, 0.35, and 0.44. The standard similitude parameter, when applied to interpret crack growth rate data, yields distinct Paris curves for each displacement ratio under the block load sequence test procedure employed in this study, thereby violating the fundamental similitude hypothesis. This is due to fiber bridging, at a composite–metal interface. The fatigue resistance curve (R‐curve) is employed to interpret fiber‐bridged fatigue crack growth, utilizing a normalized crack growth driving force parameter. The fatigue R‐curve is observed to be load ratio dependent. In this work, a modified normalized similitude parameter is introduced to characterize fatigue behavior under the combined effect of fiber bridging and displacement ratio. This parameter unifies fatigue data varying across fiber bridging levels and displacement ratios into a single master curve.