To determine the strength of adhesive connections, standard test specimens are bonded in the laboratory. The substrate fracture is a specific type of fracture of these standard test specimens.

A distinction is made between, among others, the following types of fracture:

• Break between adhesive and part to be joined: adhesive break (adhesion)
• Fracture in Adhesive: Cohesive Fracture (Cohesion)
• Fracture of the adherend: Fracture of the adherend/substrate fracture
• Different forms of mixed fracture
• Material tear-out, material delamination (e.g. in fiber-reinforced plastic).

If the break occurs entirely outside the adhesive layer, the strength of the adhesive is greater than the inherent strength of the substrate or the broken substrate part.

This break is referred to as a cohesive break in the substrate material or simply as a substrate break.

In contrast to the boundary layer break on the part to be joined, a substrate break runs completely through the material of the substrate that is unaffected by the bonding.