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This research presents a comparative analysis of the fracture surfaces of adhesively bonded dissimilar single lap joints (DSLJs) and investigates the effect of nanosilica (NS) additives on their fracture behavior and performance. The study focuses on DSLJs composed of aluminum (Al), stainless steel (SS), copper (Cu), and carbon fiber reinforced polymer (CFRP) adherends bonded with an epoxy adhesive. The fracture surface of DSLJs is further analyzed by introducing two parameters: fractional total fracture area (aT) and the surface sensitivity of each adherend (aSurface). These parameters serve as benchmarks to predict the final load capacity of the adhesive joints. It is found that a decrease in aT and an increase in the sensitivity of the adherend with a lower Young's modulus lead to higher load capacity. Tensile tests revealed that incorporating NS up to a critical weight percentage of 0.6 wt% improves the proposed surface parameters and significantly contributes to higher levels of load capacity and absorbing greater amounts of energy to failure. Furthermore, numerical simulations offer insights into stress distribution and the mechanism of plastic deformation propagation, providing additional support for the experimental findings. Highlights: NS up to 0.6 wt% enhances the mechanical properties of DSLJs.NS–epoxy interactions characterized through Fourier transform infrared and transmission electron microscopy analysis.Fracture surface patterns help to predict the final load capacity of DSLJs.Plastic propagation in epoxy verifies fracture surface pattern in DSLJs. [ABSTRACT FROM AUTHOR]