The effect of defects on the cyclic behavior of polymeric 3D kirigami structures

Recent advances in the assembly of three-dimensional (3D) structures driven by compressive buckling have provided an opportunity to exploit the capability in a broad range of engineering applications. These include microelectromechanical systems, energy storage, and wearable electronic devices. The occurrence of defects during fabrication and assembly, or during operation could impact the performance of the devices. Herein, we investigate the mechanical cycling of structures with different types of structural defects, including the presence of a pre-existing crack, structures with a thinner leg, and a pre-buckled leg. Studies of compressive cycling response of these microscale 3D polymer-based kirigami architectures revealed stiffening behavior for both defective and non-defective structures. Structural densification, developed internal stress, and deformation of the elastomer substrate were the reasons for stiffening. Cyclic compression was performed to 50% and extreme condition of 100 % of the initial height using in-situ scanning electron microscopy. The structures were found to achieve stable hysteretic cycling with steady-state mechanical response after a number of cycles. The deformation behavior, the structure stability under cyclic loading, and the load bearing capability were found to be dependent on the defect type, but they were not catastrophic.