Investigating the Tear Fracture of Elastomeric Skins in Morphing Wings: An Experimental and Computational Study

Abstract

Morphing wings covered with elastomeric skin have emerged as a promising technique for enhancing the performance and efficiency of unmanned aerial vehicles (UAVs). These morphing wings can change shape in flight, enabling UAVs to adapt to evolving aerodynamic conditions, fly more efficiently, maneuver more effectively and perform a broader range of missions. The durability of such elastomeric skins that cover the wings, on the other hand, is a critical issue that requires careful consideration. During the flight, elastomeric skins are subjected to a variety of mechanical stresses, including tear and fracture, which can significantly impact the performance and reliability of elastomeric morphing wings. To ensure the long-term durability of the morphing wings, a comprehensive understanding of the tear fracture of elastomeric skins is essential. This study employs a multi-faceted approach of experimental and computational research to investigate the tear fracture of elastomeric skins in morphing wings. Initially, the fracture properties of three materials — Latex, Oppo and Ecoflex — are evaluated experimentally for various cut positions. Subsequently, a continuum physics-based tear fracture model is derived to numerically simulate the mechanical behavior of elastomeric skins. The Griffith criterion, a well-established method, is adopted to investigate mode-III fracture tests, specifically the trousers test, which involves pulling two legs of a cut specimen horizontally apart. Finally, the derived tear fracture model is validated by comparing model solutions to tear test data obtained experimentally. The study suggests that adjusting the stretch ratio and cut position can significantly impact the stress distribution of elastomeric skins, the ability to resist fracture and the stretching behavior of elastomeric morphing wings.