INVESTIGATING THE SECONDARY BUCKLING OF THIN FILMS WITH A MODEL BASED ON ELASTIC RODS WITH HINGES

Thin films are usually submitted to high residual compression stresses which cause them to delaminate and buckle. We focus on the case in which delaminated areas take the form of long rectangular strips. The most commonly observed buckling equilibria that develop on such strip-delaminated areas are the straight-sided wrinkle, the row of bubbles, and the telephone cord wrinkle. An analytical model, based on elastic rods with hinges and taking into account the contact between film and substrate, is set up for the study of the post-buckling regime of the transition from straight-sided wrinkles to bubbles. The existence of snap-through is investigated; previous numerical studies revealed that this phenomenon can sometimes occur. The present analytical approach excludes numerical artifacts that can easily arise due to the high sensitivity of this problem to initial imperfections. The model reveals a critical bubble aspect ratio associated with the snap-through, and the existence of several simultaneous bubble equilibria.