Secondary telephone cord buckle in thickness gradient and tapered delamination

Abstract

We investigated the formation of telephone-cord buckling patterns in stressed nickel thin films deposited by ion beam sputtering on polycarbonate substrates with a controlled thickness gradient. Initially, the application of an external compressive stress induced straight-sided buckles in the nickel films. Upon releasing the applied stress, these buckles transformed into telephone-cord patterns oriented parallel to the thickness gradient, exhibiting stripe widths that varied accordingly. Experimental observations revealed that both the wavelength and width of the telephone-cord buckles decreased with decreasing film thickness. To further understand this behavior, finite element method simulations were performed to systematically study the effects of film thickness, stripe-width gradients and internal stress on the buckle wavelength. The numerical results are presented and compared with experimental data, showing good agreement and providing deeper insight into the mechanics of gradient-induced buckling in thin films.