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What factors determine the strength of an adhesive joint?

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Why does glue stick? — adhesive Overview of how glue and other adhesives work.

The strength of an adhesive joint is determined by a complex interplay of physical and chemical factors. The primary determinants include the properties of the adhesive itself, the nature of the adherends (the components being joined), and the quality of the surface pretreatment or primer.1

For a strong bond to form, the adhesive must effectively wet and spread across the surface to achieve intimate molecular contact. Once this contact is established, strength is generated through several mechanisms, including:1

Adsorption: Intermolecular or valence forces between the surface layers of the adhesive and the adherend.1
Mechanical Interlocking: The adhesive flowing into pores or around projections on the adherend surface.1
Interdiffusion: The liquid adhesive dissolving and diffusing into the adherend material.1
Chemical Reaction: Adsorption combined with a chemical reaction between the adhesive and the solid surface.1
Electrostatic Attraction: Forces developing between materials with differing electronic band structures.1

Ultimately, the composition of the interphase—the transitional zone between the adhesive and the adherend—controls the joint's durability and its ability to transfer stress. Joint design and the specific method of load application further influence the mechanical behavior and overall performance of the bonded structure.1