Studies on Sheet-Metal Compounds with Piezoceramic Modules for Icing Detection and De-Icing Thomas Mäder,* Matthias Nestler,* Burkhard Kranz, and Welf-Guntram Drossel The authors aim at laying the foundations for the use of sheet-metal compounds with integrated piezoceramic modules in airplanes or wind turbines. The utilization of piezoceramic modules in aerofoils and rotor blades enables material integrated icing detection or de-icing. An innovative production technology allows for the integration of piezoceramic modules in sheet-metal parts. The modules are placed inside an aluminum sheet sandwich structure surrounded by an adhesive layer. A beam for bending with a local sandwich build-up and an integrated piezomodule is manufac- tured. The measurement of impedance and phase is used for identification of resonance frequencies. Resonance frequencies change when icing occurs because of its additional mass. First tests on the bending beam identified frequency ranges favorable for icing detection and vibration assisted de-icing. For this purpose, icing is performed inside a cooling chamber at 25  C. Furthermore, a demonstrative aerofoil structure (DAS), based on a previously used demonstrator for health-monitoring, is redesigned and built. Several piezomodules are integrated on positions identified as suitable by a finite element (FE) analysis. The structure with integrated piezomodules is also tested inside the cooling chamber. Icing is detected at the bending beam and the DAS. De-Icing is possible by means of integrated piezomodules in the bending beam. The obtained results provide information to develop strategies for the use of integrated piezomodules in icing detection and de-icing systems. 1. Introduction into De-Icing Technologies De-Icing and anti-icing strategies for aircrafts are relevant during flight as well as in take-off and landing. Due to weather conditions, icing of aerofoils is sometimes unavoidable. Icing mainly forms at the leading and trailing edges and negatively affects aerodynamics by causing turbulent flow and reducing lift. Thus, de-icing concepts are to be provided. [1,2] Two different kinds of ice and their mixture can be formed during flight, glaze, or clear ice and rime ice. Glaze ice builds up by super-cooled water drops hitting the cold surface of the airplane. This ice is dense, clear, and smooth. It can form thick layers, disturbs aerodynamics the most, and is difficult to remove. Rime ice is an aggregation of ice particles and is more incoherent and has a milk-like appear- ance. [3] At the airfield operational de-icing is mainly realized by spraying de-icing fluid (e.g., propylene glycol-based aircraft deic- ing fluid) or in some cases by infrared radiation. [4] During flight, ice has to be detected before de-icing starts. Typical sensors in operation use vibrating ele- ments, hence ice is detected by a change in resonance frequencies due to the addi- tional mass of ice. [1,3] Furthermore, the use of optical systems is possible. When ice appears, reflectivity of a reflecting wall decreases leading to a manipulation of the light signal. [5] Ultrasound ice accretion sensors are in development. [6,7] The contri- bution of Gao et al. gives good overview to ice detection systems. [3] De-icing during operation in flight is mainly performed by hot air from the engine, electric heating elements, inflatable boots, or chemicals. [8,9] The introduction of Endres et al. gives a good summary over all techniques cur- rently used in operation. [9] Current state of research are furthermore heatable paints or shape memory alloys aiming at breaking off the ice. [10] Other fields of research are the use of vibrations in non-stiffened wing- structures as well as alternative surface coatings aiming at a reduction of ice adhesion. [11] Main focus is a decrease of the high energy consumption of previous solu- tions. [2,9,11] A de-icing system for a protective housing mounted on an aircraft structure was also described. [12] Here, piezo- electric drives are used for monitoring of icing and de-icing. The authors propose the use of piezoceramic modules for ice detection and de-icing. In contrast to ref. [12], piezomodules should be directly integrated into the aerofoil using an innovative manufacturing process and a local sandwich build-up. A patent proposes the use of integrated piezomodules in aerofoil structures made of fiber-reinforced composite material. [13] The piezomoduls consume only a fraction of the energy compared to heating solutions, which takes about 4 kW m 2 for heating in cycles. [14] The energy consumption depends on the density of piezomoduls over the area, which is constrained by the mechanical properties of the structure. The only application of this integrated piezomoduls are drones so far. Most of the civil airplanes and their wing structures are made of metal sheets. So there is no such solution for civil aircraft wings made of metal. The focus of this work therefore is on the integration of Dr. T. Mäder, Dr. M. Nestler, Dr. B. Kranz, Prof. W.-G. Drossel Fraunhofer Institute for Machine Tools and Forming Technology IWU Reichenhainer Strasse 88, 09126 Chemnitz, Germany E-mail: thomas.maeder@iwu.fraunhofer.de; matthias.nestler@iwu.fraunhofer.de DOI: 10.1002/adem.201800589 www.aem-journal.com FULL PAPER Adv. Eng. Mater. 2018, 1800589 © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1800589 (1 of 9)