adherend

An adherend is the surface or material to which an adhesive is applied to form a bonded joint. It acts as one side of the bond, while the adhesive provides the joining medium. The term is used across adhesives, coatings, and composite laminates to distinguish the substrate from the adhesive layer.

Common adherend materials include metals such as steel and aluminum, polymers including thermoplastics and thermosets, fiber-reinforced composites (carbon fiber and glass fiber), ceramics, and wood. The choice of adherend affects bond durability, dimensional stability, and resistance to environmental conditions.

Surface preparation is critical for good adhesion. It typically involves cleaning to remove oils and contaminants, drying, and surface modification to increase wettability and mechanical interlock. Treatments include mechanical roughening, chemical primers, plasma or flame treatment, oxidation, and coupling agents like silanes.

Adherend properties such as surface energy, roughness, chemical composition, and cleanliness influence bonding performance. Joint design, adherend thickness, and curing temperature also affect stresses at the interface and the probability of failure. Compatible adherend–adhesive systems are chosen to resist service conditions.

Failure modes include adhesive failure at the interface, cohesive failure within the adhesive, or adherend failure near the interface. Tests such as lap shear, peel, and fracture toughness assess adherence of adherends under service-like loads.