Indentation for evaluating cracking and delamination of thin coatings using finite element analysis

• Both the coating cracking and interfacial delamination were taken into account.
• The interplay of coating cracking and interfacial delamination was investigated.
• Effects of coating elastic modulus and thickness on its durability were obtained.
• A cohesive zone model was applied to simulate the damage process.

The mechanics of indentation induced coating cracking and interfacial delamination in a typical weakly bonded brittle thin coating-substrate system (diamond-like carbon coating with low adhesion on steel substrate) is investigated by using finite element method. A bilinear cohesive zone model with prescribed cohesive strength and energy is applied to simulate evolutions of the crack and delamination. The effects of the cohesive zones, coating elastic modulus, and coating thickness on the indentation response are evaluated. It is found that increasing the cohesive strength/energy of coating reduces the probabilities of crack generation and propagation, whereas increases the susceptibility to interfacial delamination. At a critical value of the cohesive strength of the bonding layer, the resistance to interfacial delamination reaches its minimum. Nevertheless, the coating cracking is not sensitive to the interface adhesive properties. Moreover, a coating can receive better protection with lower coating elastic modulus. Additionally, increasing the coating thickness generally increases the critical load for coating/interface failures, but opposite effect occurs when the coating is thinner than a critical thickness. Numerical results have also been compared with other emulational or experimental works, and can establish a theoretical basis for improving the durability of brittle thin coatings.