Short for film tear bond. When a peel or shear coupon tears through the parent sheet next to the weld instead of along the bond line, the weld has proved at least as strong as the sheet, which is the result inspectors want. A non-FTB break, where the weld peels apart, fails even if the force was high. ASTM D6392 assigns more detailed locus-of-break codes, but FTB is the everyday shorthand.
All five peels FTB and strength is above spec, so that trial weld is good to go.
Also heard as
- film tear bond
Related terms
Peel test
Seam test that pulls the top sheet away from the bottom sheet across the weld to check how well they fused.
Shear test
Seam test that pulls the two sheets apart in their own plane, loading the whole weld in shear.
Coupon
Narrow strip cut across a seam sample for peel or shear testing, usually one inch wide.