Multiple cracking of brittle coatings on strained substrates

Multiple cracking of well-adhered brittle coatings on strained substrates has been commonly observed in many coating applications. Here we found two significant uses for this cracking phenomenon. First, if crack density as a function of applied strain is measured at one coating thickness, it can be used to predict those for other coating thicknesses. Second, if the residual stress in the coating is unknown, the crack density versus applied strain relation can be used to deduce this residual stress. The key to our method is to obtain a master curve by normalizing the crack density and the applied strain, respectively, by the coating thickness and the critical applied strain in initiating cracking.