Monitoring Crack Tip Position in Adhesively Bonded Joints Under Mixed I+II Mode Loading

The use of adhesive joints has gained favour in recent years, due to their capacity for weight reduction, improved stress distribution, and enhanced fatigue resistance. However, the widespread use of adhesive joints in structural applications is hindered, because reliable and mature inspection and defect detection techniques are not yet available. Adhesive joints in structural applications are subject to fatigue loading, during which debonds can initiate and propagate, ultimately leading to potential failure. In the majority of cases, joints operate under mixed-mode loading conditions. In this work, a steel Cracked Lap Shear specimen was tested to investigate the crack growth behaviour of adhesive joints under mixed I+II mode loading. To address the challenge of monitoring these joints, a range of experimental techniques was employed. These techniques included Visual testing, Digital Image Correlation, and Optical Backscatter Reflectometry. The different methods were evaluated and compared to determine their effectiveness in locating the crack tip within joints during fatigue propagation.