Lap shear test

A test that measures the force needed to progressively separate a bonded joint or laminated layer by peeling, usually at a defined angle such as 90 or 180 degrees. It is used on adhesives, coatings, laminates and roofing membrane seams, where peel loading is typically the weakest mode of a bond.

An adhesive designed to carry significant service loads as part of an engineered joint, transferring stress between substrates over the whole bonded area rather than at discrete fasteners. Epoxies, polyurethanes and methacrylates are the main chemistries, used in applications from aircraft assemblies to wind turbine blade bonding.

Failure of a bonded joint within the body of the adhesive itself, leaving adhesive on both substrates, as opposed to adhesive failure at the interface. In joint testing it is generally the preferred failure mode, because it shows the bond to each substrate was stronger than the adhesive, so the adhesive's full capability was realised.