This study examines the mechanical behavior of dissimilar single lap joints (DSLJs) formed by bonding metallic and composite adherends using an epoxy adhesive. A distinct softening phase was observed, characterized by a reduction in the load-displacement gradient, particularly in joints with metallic adherends of lower elastic modulus. This premature softening led to early failure and reduced ultimate load-bearing capacity. The failure mechanisms were influenced by interfacial debonding in metallic adherends and delamination in CFRP composites, significantly affecting the joint strength. Fracture surfaces were analyzed quantitatively, leading to the development of mathematical loci that describe the relationship between fracture area and ultimate load. These loci consistently indicated that a larger total fracture area corresponded to a lower ultimate load. Additionally, an extremum line equation was derived, providing a novel approach to evaluating primary failure mechanisms and load capacity in DSLJs. This parametric analysis offers valuable insights into optimizing joint performance by examining the effects of surface characteristics and adhesion properties on mechanical behavior, aiding in the design of more reliable dissimilar material joints.
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