PSI - Issue 69

Stefano Rodinò et al. / Procedia Structural Integrity 69 (2025) 20–25

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1. Introduction Active composite materials, incorporating shape memory alloys (SMAs), represent a significant advancement in adaptive surface technologies across various engineering domains. These composites exhibit unique properties, enabling multifunctional capabilities and enhanced structural performance. As established by Lagoudas et al. (2008), SMAs represent a distinctive class of metallic materials capable of recovering their original shape following substantial mechanical deformation through either thermal or mechanical stimuli. This behavior stems from fully reversible transitions between two crystallographic structures: the body-centered cubic austenite (A) and the monoclinic martensite (M). The inherent shape memory characteristics make these materials particularly suitable for developing adaptive structures with shape morphing capabilities, as demonstrated in comprehensive reviews by Sellitto et al. (2019) and Kim et al. (2023). Further investigations by Sgambitterra et al. (2023) and Rodinò et al. (2024) have established fundamental frameworks for characterizing the thermo-mechanical response of such systems. In the automotive sector, significant advancements have been achieved, as documented by Sellitto et al. (2019), Perrone et al. (2022) and Riccio et. al. (2024), demonstrating enhanced efficiency and performance through SMA integration. However, despite their unique functional features, the practical implementation of SMA-based polymer composites faces several critical challenges. Primary among these is the adhesion at the SMA-polymer interface, as investigated by Rodinò et al. (2022) and Zhao et al. (2018). Lacasse et al. (2014) highlighted that these interface considerations become particularly critical when considering the large recovery forces and temperature variations during SMA thermal activation. These challenges can lead to delamination phenomena, especially under repeated actuation cycles, as documented in detailed studies by Zhou et al. (2009) and Woodworth et al. (2022). The present investigation addresses these fundamental challenges through experimental characterization of a novel SMA-driven active composite, specifically designed to overcome interface adhesion issues through a multi-material approach. This study employs systematic wind tunnel experiments to evaluate the shape morphing response under various loading conditions, contributing to the understanding of active composite behavior in realistic operating conditions. The findings provide valuable insights for future design optimizations of SMA-based adaptive structures. The experimental investigation focused on a layered multi-material composite incorporating shape memory alloy (SMA) actuators. The active material consisted of commercial Nickel-Titanium-based shape memory alloy wire (SmartFlex, SAES Memry, USA) with a diameter of 300 µm. This NiTi wire exhibited specific transformation temperatures: martensite start temperature ( ! " ) of 44°C, martensite finish temperature ( # " ) of 24°C, austenite start temperature ( "! ) of 62°C, and austenite finish temperature ( #" ) of 75°C, where the temperature-stress dependence coefficient are C M = 7.5 MPa/°C for martensite and C A = 11 MPa/°C for the austenite. The composite architecture employed a strategic multi-layer design to address interface challenges identified in previous studies (Rodinò et al., 2024). The composite structure integrated two distinct polymeric layers: a stiff structural component composed of PC+ABS (Polycarbonate + Acrylonitrile Butadiene Styrene) and a compliant layer manufactured from high temperature Silicone. Table 1 presents the key mechanical properties of these constituent materials. Table 1. Mechanical properties of polymeric components utilized in the active composite. Material Young's modulus (MPa) Poisson's ratio Tensile strength (MPa) Elongation to fracture (%) PC/ABS 2100 0.4 46 60 HT Silicone 27 0.48 10 >100 The geometric configuration of the composite specimen was carefully designed to optimize shape morphing capabilities while maintaining structural integrity. Table 2 provides the critical dimensional parameters of the manufactured prototype depicted in Fig. 1. 2. Materials and Experimental Methods 2.1. Active Composite Design and Manufacturing