On the morphology of buckling structures in a controlled-thickness gradient: Finite element method and experimental studies

We investigated straight-sided and telephone cord buckles on stressed nickel thin films deposited by ion beam sputtering on polycarbonate substrate and exhibiting a controlled thickness gradient. It is experimentally observed that the height of the straight-sided buckles aligned parallel to the thickness gradient decreases as the film thickness increases. When these buckles are oriented perpendicular to the gradient, they result in an asymmetrical profile with a maximum deflection shifted towards the thinner part of the film. Additionally, we explore the characteristics of telephone cord buckles, showing that their wavelength decreases as the local film thickness decreases. Finite elements method simulations were performed to systematically explore the influence of various thickness gradients on buckles. The numerical results are presented, compared to the experimental results and discussed.