Experimental Study on Surface Instabilities in FDM Printed Specimens under Compression

This study looks into the development of wrinkles in a bilayer fused deposition modeling (FDM)-printed system. The specimen is composed of two polymeric materials (ABS and TPU) to emphasize the difference in stiffness between the two layers, i.e., the film and the substrate. The specimen production process allows to take into account a variety of printing parameters, including infill density, the number of film layers, and printing orientation. During the experimental stage, a distributed compressive force is applied to the specimens, which are confined so as to avoid out-of-plane instabilities, allowing wrinkles to form. The research shows that surface instabilities can develop in the surface film depending on the stiffness mismatch and resulting in variations in the wrinkles' magnitude and wavelength during compression. Furthermore, the study observes the transition from wrinkles to folds (creases). The results of this study are a step forward in explaining the mechanisms that govern surface instabilities and promoting advanced application in future research. In fact, understanding the formation of wrinkles in bilayer membranes with a limited stiffness mismatch will allow the development of soft printed matter with adaptable properties that are easily applicable, for instance, in the fields of soft robotics and biomedical engineering.