Comparative study of impact and static indentation tests on particulate-filled thermoplastic fluoropolymer coatings

Abstract

This study investigates the performance of particulate-filled thermoplastic fluoropolymer coatings under both dynamic impact tests and static indentation tests. An instrumented impact testing rig was used to measure the impact energy, impact velocity, acceleration and impact force during the impact tests. Coating samples with different thicknesses of coating layers and steel substrate were impact tested to investigate the effect of coating and substrate thickness on the impact response and damage to the coatings. The data obtained from the dynamic tests were used to calculate the Meyer hardness values of the coating and compared with the Meyer hardness results obtained from Brinell indentation tests on the coating. The Meyer index m was similar under dynamic impact and static indentation testing conditions. The Meyer hardness calculated from the impact tests does not change markedly as a function of depth of penetration normalised to the thickness of coating, whereas the Brinell hardness increases with the depth of penetration to coating thickness ratio. For a given value of indentation strain, the Meyer hardness calculated from the maximum force measured in the impact test is approximately 2.5 times that resulting from the Brinell test. This reflects the fact that the higher strain rate in the impact test would give rise to a higher flow stress and thus hardness.