Surface Tolerant Adhesives for Bonded Airframe Structures

Structural adhesives with silicone-tolerant characteristics (surface tolerant adhesives) were developed, aiming to find solutions to overcome silicone contaminations present at bonding surfaces. This study overviews mechanical performance aspects of the surface tolerant adhesives with composite-to-composite and composite-to-titanium joints, where contaminated adherends were spray-coated with predetermined amounts of silicone (mold release) solutions. Shear strength values, in single lap shear mode, revealed a shear strength retention of up to nearly 80% in contaminated bonded joints with surface tolerant adhesives, when compared to nearly 20% strength retention with a control (standard aerospace-qualified) adhesive. In Mode I fracture, a substantially large resistance to fracture (cohesive-type failure) was observed with the surface tolerant adhesives, whereas a pure adhesive-type failure was observed in the control adhesive. Mechanical performance and relevant surface analyses of surface tolerant adhesives are detailed in this study.