Mode II strength of co-bonded adhesive joints at different strain rates

Bonded joints in composite structures are subjected to crash scenarios and their mechanical behaviour can depend on the strain rate. However, their dynamic characterization remains not fully standardized due to the difficulty of isolating the dynamic effects from the actual behaviour of the adhesive. The present study addresses this issue by developing, via finite element (FE) simulations, a slotted single-lap shear (SLS) specimen with a new set of dimensions tailored for pure mode II testing of co-bonded adhesive joints under quasi-static (QS) and dynamic conditions. This geometry is consistent with the manufacturing constraints of the Carbon-Fiber Reinforced Polymer (CFRP) adherents. The main novelty is the design of a custom metallic tooling to enhance dynamic equilibrium, reduce bending, and improve repeatability. Using Split Hopkinson Pressure Bar (SHPB) testing combined with Digital Image Correlation (DIC), results show that dynamic shear strength increases relative to the QS reference, but decreases at higher strain rates. The optimized set-up provides reliable data to support advanced modeling of composite structures under dynamic loading. • Single Lap Shear joint with CFRP adherents & tooling: mode II & dynamic equilibrium. • Finite element simulations guide test design and reproduce observed behavior. • Dynamic shear strength exceeds quasi-static but decreases at high strain rates. • High-speed DIC is essential; Hopkinson-bar analysis overestimates strain rate by 50%. • Failure is adhesive under pure mode II across the investigated strain rates.