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LE coupon based technology

Final Report Summary - SMYLE (LE coupon based technology)

SMyLE proposes a technological research program allowing to develop, manufacture and validate actuators by integrating a number of various emerging SMA technologies that result in high performance/ high reliability actuators. The innovative aspects of the proposed technologies are new SMA material concept with high power-to-weight ratio and high performance & reliability optimized for later application into a morphing/adaptive wing. Thanks to these new technologies, the SMyLE actuator system could contribute to lower mass (compared to a conventional mechanical/hydraulic actuator), be fully integrated (at a later stage) into the leading edge of an adaptive wing system, i.e.: at first, SMyLE can significantly improve the aerodynamics at the LE vicinity since it offers a greater operational envelope compared to a conventional LE slat device. Secondly, it can serve as deicing protection device, therefore eliminating heavy conventional, as well as electrically demanding, deicing systems. As third, it can be further utilized as a flight control surface replacement, locally improving the aerodynamics in the LE vicinity during flight.

Project Context and Objectives:

Wings of modern transport A/C are designed to provide the optimal aerodynamic characteristics (the best lift-to-drag ratio) at cruise flight conditions, e.g. within the transonic velocity regime. Conclusively such an aerodynamic profile becomes ineffective for low-speed, particularly during take-off & landing.

An approach that has gained a lot of popularity combined with the advent of smart materials is to alter the (local) camber of the A/C's wing in order to achieve the desired aerodynamic performance at all flight configurations. Shape Memory Alloys (SMAs) have demonstrated their suitability for many static applications due to their high structural integration potential and remarkable actuation capabilities. A widely accepted understanding of 'Smart' is that the material possesses sensing, actuation and control capabilities. SMAs can sense temperatures as a function of change in damping, stiffness, electrical resistivity and deflection. It is specifically the latter aspect which has made SMAs highly interesting, since it is the actuation function built into the material. In general, SMA elements are capable of producing large strains, up to 4% for two-way training and for large actuation forces up to 10% strain when deformed into a non-linear fashion. Furthermore, SMAs are capable of actuating in a fully three-dimensional manner, allowing the fabrication of actuation components which extend, bend, twist, or provide a combination of these and other deformations. The pseudo-elastic effect of the SMA elements provide two very useful additional advantages, (a) a non-linearity which allows vibration isolation and large recoverable deformations and, (b) accompanying hysteresis which can dissipate energy and hence reduce vibration-induced loads. As a result, the benefits of SMA actuators compared to their hydraulic counterparts are strongly evident in simplicity, voltage requirements, silence and means of achieving control. In conclusion, Shape Memory Alloys have become particularly attractive as actuating devices compared to their conventional, heavy, hydraulic actuators counterparts since they allow to exhibit large strains & permanent deformations that disappear upon an increase in temperature (i.e. shape memory). Although the benefits of SMA actuators compared to their hydraulic counterparts are strongly evident, however there are disadvantages remaining still unresolved. SMA elements might exhibit loss of actuation after repetitive cyclic loading. A possible rapid heat transfer through SMA wires might be problematic due to their high-heat capacity and density. Moreover it is proven that the displacement control of the SMA elements is difficult to be achieved. These facts lead to a very caution application of the SMA elements.

In the above context, SMyLE proposes a technological research effort allowing to develop, manufacture and validate actuators by integrating a number of various emerging SMA technologies that result in high performance/high reliability actuators. The innovative aspects of the proposed technologies are new SMA material concept with high power-to-weight ratio and high performance & reliability optimized for later application into a morphing/adaptive wing. Thanks to these new technologies, the SMyLE actuator system could contribute to lower mass (compared to a conventional mechanical/hydraulic actuator), be fully integrated (at a later stage) into the leading edge of an adaptive wing system.

The purpose of SMyLE is technology based on high performance material & optimized architecture and it is multifold. When applied to the LE of an adaptive wing (at a later stage), the following benefits are expected to be strongly evident, i.e.: at first, SMyLE can significantly improve the aerodynamics at the LE vicinity compared to a conventional LE slat device. Secondly, it can serve as de-icing protection device, therefore eliminating heavy conventional, as well as electrically demanding, deicing systems. As third, it can be further utilized as a flight control surface replacement, locally improving the aerodynamics in the LE vicinity during flight. In addition, it can further serve as de-icing device ; therefore further contributing into the overall A/C weight reduction.

The main aim, in other words the output, of SMyLE is to provide a functional coupon surface strip utilizing Shape Memory Alloy (SMA) technology.

The main objectives of the project were:

- Identification of SMyLE specimen candidate architecture.
- Surface properties and the role of surface in fatigue.
- Choice of constitutive model, assumptions, simplifications and model's requirements, Finite Element (FE) model.
- Estimation of SMA material's parameters.
- Loading conditions (thermo-mechanical & electrical), hysteresis aspects. Requirements for possible bonding along both sides (i.e. short & long).
- Determination of experimental conditions, i.e. uniform- & nonuniform actuation.
- Manufacturing of a first sample and testing under clamped in a stress and/or tension/compression (T/C) scenario.
- Mechanical response of the actuator as a function of temperature & load.
- Training of SMA specimen.
- Examination of specimen operation after testing. Identification of aging and/or fatigue mechanisms. Redundancy aspects.
- Stability of material response under cyclic actuation at constant & differential stress levels.
- Thermal-cycling experimental work (i.e. evaluation of temperature effect by completing several actuation cycles at temperatures near the SMA
transformation temperature).
- Consideration of fail-safe issues, (e.g. possible recovery action, wire integrity, etc).
- Design of 3 different SMA actuated LE configurations.
- Manufacturing of number of samples of 3 different configurations and testing under clamped in a stress and/or tension/compression (T/C) scenario.
- Mechanical response of the actuator as a function of temperature & load.
- Experimental Modeling of SMA Actuators via NARX models.
- Modification of numerical model and structural correction of the SMA specimen in case of unsatisfactory experimental outcome. Final SMA specimen
deliverance. Recommendations for future work.

Project Results:

The work performed in the current project followed consequently the described objectives: An extensive literature review on SMA based actuators and relevant science and technology has been carried out. In this, the most updated technological issues of the SMA applications have been highlighted and the current applications of the technology presented. The general theory of SMA and their advantages and disadvantages have been discussed. Issues like SMA training, static and fatigue performance has been presented and the thermodynamic behavior has been assessed in terms of constitutive equations. The basic concepts for applicable actuators have been presented and some initial considerations of load capacity have been assessed. Configuration of the SMyLE actuator principles have been proposed and analyzed and the mechanical-, thermal-, electrical- and hysteresis aspects of the SMyLE actuator investigated.

Selection of constitutive model, assumptions, simplifications and model's requirements have been specified and implemented by a Finite Element (FE) model. Choice between micromechanics-based constitutive model (MMCM) and phenomenological constitutive model (PCM) resulted in the adoption of the PCM model for the rest of the project. The parameters of the PCM model have been identified through appropriate experimental procedures. Definition and execution of SMA wire training procedure for mechanical behavior stabilization have been performed. The concept perception involves the development of an SMA functional specimen having in mind the scenario for integrating the output of SMyLE into an adaptive wing's LE (at a later stage). As planned, the most promising concepts have been bench-tested to evaluate characteristics and highlight challenges.Two different SMA actuating principles have been pursued. In the first approach the actuator has been embedded in the coupon in the form of an active layer. This is similar to the composite material layered concept only in this case one or more layers will be capable of inducing predefined and controlled deformation within the structure.The second investigated approach is based on morphing the internal structure of the wing by deforming the LE of a rib as a compliant mechanism. Different compliant mechanism configurations have been proposed and numerically analysed within FE software. The most efficient rib concepts in terms of morphing capabilities have been manufactured and integrated on a test rig for experimental characterizations. A third concept in the form of a linear actuator has been designed and manufactured as well but only for concept demonstration. Three actuator concepts have been tested in this context: Single SMA wires, embedded SMA wire actuators and a compliant Leading Edge concept. In all concepts, the provided actuation is done by applying current and heating up the SMA to the transformation temperature utilizing a control system based on thermocouples at the actuator. The shape of the specimen has been measured using LVDT measurements at selected areas. These readings could be used as feedback for the control system. A series of actuating principles have been tested from unidirectional SMA wires at different directions to 2D wire mesh configurations. Redundancy and efficiency issues have been taken into account by considering a thread of more than one SMA wires, as actuation element, where applicable. In this way the actuators are less stressed and a fail-safe approach is promoted. In all cases the LE deformation target (tip deflection vs temperature) was achieved. SMyLE post-experimental issues have been considered and recommendations for future work described. Presentation of a complete methodology for identifying the SMA actuator dynamics based exclusively on experimental measurements, without the need of analytic modelling has been provided whereas a model of simulating (that is obtaining the model output based only input values) the SMA deformation has been developed. The proposed NARX (Nonlinear AutoRegressive with eXogenous excitation) -based approach has been assessed through the application of this methodology to a representative case of a simulated composite beam, equipped with an active SMA layer. Finally, recommendations for future work in terms of improvements towards application of the investigated technologies on a real a/c LE prototype have been formulated.

The expected final results are a lightweight novel electrically operated Leading Edge actuator with controlled shape configuration. It is expected that a family of actuator solutions can be proposed for different application in an all electric aircraft configuration.

Potential Impact:

The use of electrically powered actuators integrating speed and position sensors is expected to enable to save weight, and to increase engine monitoring and diagnostics. Moreover, SMyLE project will allow to reduce the size of components of generation equipment as well as to achieve significant reduction in maintenance. Another aspect of SMyLE developments is increased reliability because safety has a great impact in aeronautic transports.

The dissemination activities performed during the project and those planned to be performed beyond the project duration are the generation of a flyer to be presented at related international airfares and the publication of a paper AIRFOIL’S LEADING EDGE MORPHING BASED ON SMA ELEMENTS by D. Karagiannis, D. Stamatelos and Th. Spathopoulos to be presented in the following conference: 6th ECCOMAS Conference on Smart Structures and Materials, SMART2013, Politecnico di Torino, 24-26 June 2013.

At this stage the majority of exploitable knowledge is related to development of methodologies and approaches for numerical modeling of SMA based actuators. Transportation sector is the sector of application for such developments and this includes aircraft design and manufacturing, as well as shipbuilding and automotive industries. Discussions with the Topic Manager and other potential users are underway for project results and acquired know-how to be exploited in follow-on work in the context of Clean Sky such as enhancing buckling characteristics of composite panels, or to be applied in other research activities e.g.morphing of helicopter blades.