Result in a tensile bond test where the adhesive holding the test fixture fails before the coating or bond line does. The true coating strength is then unknown but higher than the reading, so it is reported as greater than the value. For dense HVOF coatings this is the expected and welcome result. Repeated glue failures at low values, though, mean the epoxy was mixed, cured or applied poorly.
All five went glue failure above 10k, report it as greater than and release the lot.
Also heard as
- epoxy failure
Related terms
Bond strength
How hard you must pull to tear a coating off its substrate, measured by gluing and tensile testing.
Cohesive failure
A bond test break inside the coating, with coating left on both halves of the test specimen.
Adhesive failure
A bond test break at the coating-substrate interface, meaning the coating let go of the base metal.
Coupon
A small test piece sprayed alongside production parts to stand in for them in destructive tests.