Wrinkling of soft bilayers created with additive manufacturing: Experimental tests, finite element modelling and analytical validation

In the leather manufacturing industry, the necessity to introduce new leather-surrogate materials is motivated by the huge environmental footprint of the leather production process. In fact, tanning requires a lot of resources, like water and energy, but also chemicals that can be harmful to the environment and the workers as well. The contribution focuses on how the mechanical characteristics of materials used to imitate leatherlike membranes can be characterised using the wrinkles caused by compressive forces. TPU and PLA, two polymeric materials frequently used in 3D printing based on FDM, are here used to simulate the grain and corium layers of the hide to recreate the skin's structure. A compressive characterization of PLA material is performed. In this work, the scientific literature on wrinkling phenomenon has been revised. Wrinkling might form on leather-like soft membranes or in thin layers supported by a substrate when exposed to compressive loading. Results of critical wavelengths determined by the analytical approach using both inputs from experiments and literature, have been finally compared to various combinations of finite element models (FEM) to provide a variety of outcomes and to certify the accuracy of the study. In conclusion, this study provides a preliminary insight regarding the characterization of a 3D-printed, bi-layered material exposed to the wrinkling phenomenon that occurs every day on leather-based products.