Mode II edge delamination of compressed thin films

Ceramic coatings deposited on metal substrates generally develop significan t compressive stresses when cooled from the temperature at which they are p rocessed as a result of.. thermal expansion mismatch. One of the main failu re modes for these coatings is edge delamination. For an ideally brittle in terface, the edge delamination of a compressed thin film involves mode II i nterface cracking. The crack faces are in contact with normal stress acting across the faces behind the advancing tip. Frictional shielding of the cra ck tip has been shown to increase the apparent fracture toughness. Roughnes s effects associated with the separating faces can also contribute to the a pparent toughness. A model of mode II steady-state edge delamination that i ncorporates combined friction and roughness effects between the delaminated film and substrate is proposed and analyzed. This model is used to assess whether frictional shielding and surface roughness effects are sufficient t o explain the large apparent mode II fracture toughness values observed in experiments.