Witness specimen, such as a flat tab, bond test button or Almen strip, mounted on the same fixture and sprayed with the same parameters as the parts. Coupons are sectioned, pulled and hardness tested so the real parts do not have to be destroyed. They only represent the parts if they are prepared from similar material and sit where the parts see the same gun path and heat.
Clip two coupons on the fixture next to the vanes, one for the mount, one for bond.
A coupon bolted to the fixture where the gun barely reaches tells you nothing about the part; place it in the hottest, thickest zone of the path.
Also heard as
- test coupon
- witness coupon
- test button
- slug
Related terms
Mount
A polished cross section of a coated coupon set in resin, used to check structure under the microscope.
Bond strength
How hard you must pull to tear a coating off its substrate, measured by gluing and tensile testing.
Shoot
Booth verb for spraying a coating onto a part or coupon.
Residual stress
Stress locked into a coating and substrate after spraying, from splat shrinkage, cooling and impact.
Same word, different worlds
A small standard test piece, usually a metal or plastic strip, bonded to check adhesive strength or prep.
Printed Circuit BoardsSmall test pattern built on the production panel and measured or sectioned to prove the boards meet spec.
GeosyntheticsNarrow strip cut across a seam sample for peel or shear testing, usually one inch wide.