Cohesive failure

Adhesive and cohesive failures are the two most common forms of adhesive bond failure.

Cohesive failures can occur both in the adhesive and in the substrate (see component failure). Unlike in the case of adhesive failure, the adhesive has not lost its adhesion to the substrate during the destruction:  adhesive continues to cover both sides of the parts to be bonded. Cohesion failures indicate that the bond is of high quality, in contrast to component failure, which indicates over-dimensioned adhesive.

Der boundary layer fracture on the substrate side is a special case of cohesive failure, in which the top layer of the substrate tears off without separating the adhesive from the substrate (adhesive failure).

Mixed fractures, in which cohesive and adhesive fractures occur at the same time, are often indications of insufficient surface preparation.