Mechanical and failure behaviors of adhesively bonded dissimilar materials joints incorporating bio-inspired morphological irregularities

Adhesive dissimilar material joints between stainless steel grade 316L and polyethylene terephthalate glycol (PETG) plastic were examined, in which irregular interface morphologies inspired by natural sutures were incorporated. The joint interfaces exhibited various teeth-like, non-repetitive zigzag patterns based on a pseudo-randomization method and sutural interdigitation index. Effects of their irregularities on mechanical and failure characteristics of adhesive butt joints were studied by means of experiments and FE simulations. The cohesive zone model, Drucker-Prager plasticity model and ductile failure criterion were applied for the interface and PETG, respectively. Predicted load-displacement curves of joints with different teeth profiles were well validated. The degree of irregularity became higher to 20 %, 40 %, and 60 %, the joint strengths decreased by 1.47 %, 5.39 %, and 11.95 %, while the total energies to failure increased by 110.74 %, 129.33 %, and 161.23 %, accordingly. More inhomogeneous morphologies led to earlier local damage initiation, but enhanced damage evolution range by impeding abrupt joint separation. Smaller teeth angles provided higher joint strength, whereas significant declines of bonding strength were observed by too acute teeth angle due to excessive stress localization and resulting teeth breakage. The teeth angle of 45° enabled the superior joint performance owing to a proper combination of interlocking and large adhesive force under shear stress state. Finally, a key insight for designing an optimal dissimilar joint with morphological irregularities was provided.