Fracture mechanics for thin-film adhesion

The essential elements of the mechanics of delamination are reviewed and their implications for design are discussed. Two important concepts for the prediction of the reliability of thin-film systems are emphasized: 1) limiting solutions for the crack-driving force that are independent of flaw size, and 2) “mixed-mode fracture.” Consideration of the first concept highlights the possibility of flaw-tolerant design in which the statistical effects associated with flaw distributions can be eliminated. The significance of mode-mixedness includes its effect on crack trajectories and on the interface toughness, two key variables in determining failure mechanisms. Theoretical predictions are given for some cases of delamination of thin films under compressive stresses, and the results are compared with experimental observations to illustrate appropriate design criteria for the model systems studied.