Recent developments in electronic devices have led to the increasing use of flexible and foldable electronics. However, a major challenge in foldable devices, such as mobile phones, is the formation of wrinkles and creases on the display surface near the fold line. These features not only compromise the aesthetic appearance but also degrade the electrical properties of the device, potentially leading to failure. This study aims to investigate the conditions for crease formation in thin films under bending deformation using the finite element method. We modeled a thin film as an incompressible Neo-Hookean hyperelastic material. Our findings reveal that unlike uniform compression, which requires an external perturbation force to initiate instability, bending deformation spontaneously formed creases. We attribute this to the non-uniform strain distribution within the material, which acts as an internal perturbation. Furthermore, creases formed directly without transitioning through a wrinkled state. The analysis showed that the creases developed at a relatively low strain level, with 98% of the model's domain having an elastic strain |εxx| < 0.28, which is smaller than the critical strain required for crease formation under uniform compression.
Kida et al. (Wed,) studied this question.