Influence of Bondline Defects on Fatigue Life of Composite Adhesive Joints Using Full‐Field Thermal Imaging

ABSTRACT Large‐scale composite structures such as wind turbine blades rely extensively on adhesively bonded joints at critical locations, which are subjected to high‐cycle fatigue throughout service. Composite adhesive joints offer relatively uniform stress distribution and require minimal surface preparation compared to mechanically bonded joints. While fabrication of thick adhesive layers inevitably contains small voids that are generally benign, larger bondline defects–particularly disbonds–can significantly influence structural performance. This study investigates the effect of controlled bondline defects (10 and 15 mm disbonds) on the fatigue behavior of adhesively bonded unidirectional glass fiber‐reinforced polymer (UD‐GFRP) joints subjected to cyclic loading. Infrared thermography (IRT) was employed as a rapid, noncontact technique to monitor the full‐field temperature evolution and the associated harmonic components generated by inelastic and dissipative mechanisms under cyclic loading, thereby enabling the assessment of damage initiation and progression. Complementary two‐dimensional digital image correlation (2D‐DIC) measurements captured full‐field displacement fields, further characterizing joint behavior. Results show that increasing disbond length leads to a measurable reduction in fatigue performance, with the larger defect producing an approximate 30% decrease in the fatigue limit and influencing the observed failure modes.