Experimental determination of mode-I traction-separation relation for DCB adhesive joints: A back face strain derived method

The widespread use of adhesive joints in automotive, aerospace, and other industries has driven research into interfacial fracture properties. Accurate determination of the traction-separation relationship (TSR) in mode-I fracture, commonly modeled with cohesive zone model, is essential for reliable design. This study proposes a back face strain derived method to directly obtain the mode-I TSR using distributed optical fiber sensors (DOFS). The validity of this method is verified through double cantilever beam (DCB) tests and compared with a direct approach using digital image correlation. The proposed approach not only captures the TSR at any moment based on the measured strain distributions ahead of the crack tip, but also tracks the evolution TSR at a specific location over time. This provides a deeper understanding of crack propagation in bonded specimens and offers new perspectives for crack monitoring and measurement. Additionally, the study discusses the crack tip captured by DOFS and provides insightful link between the cohesive zone and back face strain.