Two strips, typically 25 mm wide with a 12.5 mm overlap, are bonded and pulled in a tensile tester, as in ASTM D1002 for metals. Results are given in MPa or psi along with the failure mode. Lap shear numbers allow comparisons between adhesives and surface preps but are not true shear strengths, because peel at the overlap ends drives failure.
Lap shear averaged 22 MPa on the etched coupons but only 9 on the solvent wipe, so prep is the problem.
Overlap length on a standard coupon is short on purpose; doubling the overlap on a real part does not double its strength.
Also heard as
- lap shear strength
- single lap shear
- LSS
Related terms
Lap joint
A bonded joint where two parts overlap face to face, loading the adhesive mainly in shear.
Coupon
A small standard test piece, usually a metal or plastic strip, bonded to check adhesive strength or prep.
Cohesive failure
A break that runs through the adhesive itself, leaving adhesive on both parts.
Peel
The force needed to strip a flexible bonded layer off a surface, given per unit width.