Bond Pull testing accurately measures bond strength, as well as evaluates bond strength distributions. This helps define the reliability of bonds under stress conditions, like thermal cycles, vibration and shock.
Bond integrity is a critical parameter of coatings if they are to function properly. Bond pull testing accurately measures the bond strength of Thermal Spray and other types of coatings to their intended substrate.
Bond Pull testing is accomplished by bonding coupons between pull fixtures or by bonding special studs to the surface which allows a tensile force to be applied to the coating to determine its pull-off strength. Tests are performed on standard load frames or using specialize apparatus where a force measurement is taken and the failure strength of the tested sample is recorded.
The frame fixtures are designed to apply a force to separate the bonded loading fixture from the coated surface. They also keep the force perpendicular to the surface, which is important so as not to introduce any cleaving effect during the test, which could cause excessive variation in the test results.
Computer-controlled test frames allow bonds to be tested automatically from a stored program. Results can be analyzed and output immediately or exported in a number of database formats for subsequent analysis. Visual examinations after the test are used to characterize the nature of how the coating failed, whether in cohesive, adhesive, or mixed mode.