ANALYSIS OF THE SPONTANEOUS INTERFACIAL DECOHESION OF A THIN SURFACE-FILM

RESULTS of a numerical and experimental study of thin film delamination are reported. Spontaneous delamination is induced by a cut in a thin film attached to a substrate. The delamination is driven by the residual stress caused by thermal strain mismatch between the film and substrate. From the measured shape of the delamination, interfacial fracture criteria are examined. Parametric studies of fracture criteria are carried out numerically using a boundary integral equation (BIE) formulation. The analysis includes a new numerical scheme, based on the M-integral, for evaluating the stress intensity factor at the ends of the cut. Experiments are conducted with a polyimide film on a glass substrate. The level of residual stress is controlled by thermal strain mismatch between the film and substrate, varying the test temperature in the range of 20-255-degrees-C. Both numerical and experimental studies cover delamination of large extent. The experiment shows that the polyimide-glass interface is much tougher in the anti-plane shearing mode (mode 3). The measured interface toughness is 4.1-4.5 J/m2 for plane strain crack growth caused by tensile residual stress of the film. On the other hand, the measured mode 3 fracture toughness of the interface is 14.9-16.5 J/m2.