Loading and fracture response of CFRP-to-steel adhesively bonded joints with thick adherents – Part I: Experiments

There is a gap in the existing standardized testing procedures (ASTM and ISO) for evaluating the stiffness and strength of composite-to-metal adhesively bonded joints. Thus, there is much effort made in this field towards understanding the impact of the geometric parameters to the loading and fracture response of such joints, but limited to joints with thin adherents. On this basis, the present work provides an experimental parametric study of adhesively bonded Single Lap Joint geometries between thick dissimilar adherents. For this purpose, mild steel and CFRP laminates have been considered as the structural adherent materials. Seven SLJ geometries have been considered for fabrication and experimental testing. The SLJ specimens were tested under a uni-axial tensile quasi-static displacement. Strain gage sensors were used, in order to study their potential for monitoring damage initiation occurring in the adhesive bondline. The global response was recorded and corresponding results are presented. It was concluded that for the current material systems and geometries tested, the effect of the adhesive thickness and stiffness ratio is negligible compared to the effect of the overlap length to the stiffness and strength of the joints. The results can be utilized for analysis and design purposes of practical adhesive joints.