On the determination of coating toughness during nanoindentation

Nanoindentation tests have been widely used to evaluate fracture toughness of brittle materials. For the thin coatings, energy based models have been shown to be effective. In this study, a new energy based method is proposed based on the analysis of unloading curve at the start and end points of the crack induced pop-in. The semi-analytical generalized expressions have been presented to determine the fracture toughness of coatings under both load and displacement control. This provides valuable theoretical guideline to determine fracture toughness from the energy point of view.