In-situ investigation of temperature-dependent adhesive properties and failure modes in composite bonded joints

This paper presents an experimental investigation into the thermomechanical properties and failure modes of toughened epoxy adhesives and composite-to-aluminum bonded joints in high and low temperature conditions. First, nondestructive evaluation techniques were utilized to characterize the inherent defect morphology of bulk adhesives and the bonded joint interface. This was followed by quasi-static tensile testing conducted over a temperature range of −37 °C to 57 °C. The damage mechanisms and failure modes were investigated using in-situ digital image correlation (DIC) and high-resolution camera. The information from the morphology characterization studies was also used to reconstruct high-fidelity geometries of the test specimens for finite element (FE) analysis. The elastic properties and tensile strength of bulk adhesive test specimens showed significant deterioration while exhibiting considerable ductility at higher temperatures. DIC and FE analysis revealed the strong influence of size and distribution of defects on the material properties and damage localization. In addition, post-fracture surface characterization of the adhesively bonded specimens revealed failure modes ranging between adherent-dominant to adhesive-dominant modes at low and high-temperature conditions.