PulloffTests

Pullofftests, also known as pull-off adhesion tests, are a class of mechanical tests used to quantify the adhesive strength between a coating or film and its substrate. The test involves attaching a circular or spherical dolly to the surface with a suitable adhesive, then applying a controlled tensile load to the dolly until debonding occurs. The peak force recorded is converted to an adhesion strength by dividing by the bonded area, yielding a value typically expressed in megapascals (MPa). The method is widely used to assess coatings, paints, sealants, and thin films on a variety of substrates.

Standards for pull-off tests are provided by organizations such as ISO and ASTM. ISO 4624 and ASTM D4541 are commonly cited standards that specify apparatus, preparation, curing, loading rates, calculation, and reporting requirements. The exact protocol may vary with substrate type, coating system, and environmental conditions.

Procedure overview includes surface preparation to appropriate cleanliness and roughness, bonding of the dolly with a suitable adhesive, controlled curing time, alignment of the tester, and application of the tensile load at a prescribed rate until failure. The resulting bond strength is reported along with the observed failure mode, such as adhesive failure at the coating–substrate interface, cohesive failure within the coating, substrate failure, or dolly/glue failure.

Applications span protective coatings on concrete, metal, wood, and composites, as well as certain adhesive systems. Advantages include relatively straightforward field and laboratory use and direct measurement of adhesion; limitations involve sensitivity to surface preparation, substrate heterogeneity, and potential localized damage at the test site.