Coatings on substrates are subjected to stresses resulting from different physical phenomena, such as swelling, forming, heating, cooling and mechanical abuse. The ability of a coating to withstand these stresses depends on its physical properties generally called flexibility and toughness.
Flexibility refers to the ability of a material to undergo bending without cracks or other failures being built.
Toughness refers the ability of material to withstand instantly appearing impacts without being rubbed off, torn or broken.
Environmental conditions affect both properties considerably. Therefore tests are carried out at relative humidity of 50 ± 5% and at 25 ± 1°C. In general flexibility and toughness decrease if the coating temperature decreases.
Both properties are also considerably influenced by the strain rate. This is the rate at which the coating is elongated and is expressed in % per minute. In general flexibility and toughness decrease if the strain rate increases.
The different test equipment used to test flexibility and toughness properties of coatings can be organised into 3 groups:
Impact resistance tests
Mandrel bend tests