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An Investigation of Shape Memory Alloys as Actuating Elements in

Aerospace Morphing Applications Presented by Mr. Dimitri Karagiannis, INASCO

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An Investigation of Shape Memory Alloys as Actuating Elements in Aerospace Morphing Applications

• Morphing aerospace structures • Shape memory effect and Shape Memory

Alloy (SMA) actuators • Design tools for actuated structures • Application in aerospace morphing

Presented by Dimitri Karagiannis, INASCO

• Contributing Organisations: • INASCO • AEROTRON Research • University of Patras SAAM Group

The works have been carried out within the framework of Clean Sky SMyLE and SmyTE projects.

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Morphing aerospace structures

1. Weisshaar, T.A. (2006). Morphing Aircraft Technology-New Shapes for Aircraft Design, RTO-MP-AVT- 141, Neuilly-sur-Seine, France

http://www.cleansky.eu/content/page/clean-sky-achievements

• Morphing is a technology or set of technologies that allows air-vehicles to alter their characteristics to achieve improved flight performance and control authority or to complete tasks that are not possible without this technology1.

• One of the key enabling technologies in morphing aircraft structures is the lightweight driving actuators. Other enabling technologies adaptive structures, deformable smart skin, driving actuators, flight dynamics and flight control.

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Shape Memory Effect • A shape-memory alloy (SMA) is

an alloy that "remembers" its original shape and that when deformed returns to its pre-deformed shape when heated.

• The shape memory effect is the driving mechanism for most SMA actuator systems designed today and it is achieved through a change in the crystal structure of the material between the martensite and austenite phase.

• The first SMA to be discovered is NiTiNOL by William J. Buehler in 1961. The name is composed out of the two main elements, Ni and Ti, and the abbreviation of the Naval Ordinance Laboratories (NOL) where it was discovered.

• NiTi is the most widely used SMA .

Crystal Structure of NiTi

Lagoudas, Dimitris C, Shape Memory Alloys - Modeling and Engineering Applications

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SMA actuators • Basic NiTi SMA shapes include commercially

available wire, tube, sheet and strip basic products. These can be further processed to suit the particular application.

• In our actuating elements and mechanisms we have used manly SMA wires.

• The SMA are characterised using DSC and other methods in order to assess the phase transformation characteristics.

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SMA actuators • A stabilisation process of the thermomechanical

response of the actuator is always performed in order to insure repeatable actuation cycles. This process in called training.

• A dedicated training set up has been build and is fully functional.

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SMA basic actuation concepts • The SMA is actuated by increasing its

temperature above the phase transformation threshold. In our case, one way SMA with threshold of ~60oC was utilized.

• The most common way to heat up SMA wires is the Joule effect.

• The duration of the actuation cycle depends on how fast the SMA is heated up and subsequently cooled down. The actual alloy temperature depends on the local heat transfer coefficient.

• Control of the SMA temperature is required, as the development of high temperatures will deteriorate the actuation capability.

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SMA basic actuation concepts

Wire bundle SMA actuator Element with high force output

Flexy SMA patch ready for integration

Composite plate with SMA wires (morphing skin application)

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1D SMA actuators • SMA bundle-wire actuator is overwrapped by a heating

element in order to avoid using high power to heat up the wires and avoid any current leaks that could lead to dangerous situations. In this way the power to heat up the wires is five times less when compared to the power required by using the joule effect.

• The element is fully configurable in terms of length, number of actuators (force) and heat exchange (duration of actuation cycle).

• The period of a stroke of Δx=2.5mm and back can be accelerated from 240sec to 70sec (aircooled).

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2D actuators

Basic 2D actuator dimensions: LxD: (100 x 11)mm2, dSMA=0.1mm, Patch Thickness (tp)=0.7mm Wire Spacing (H): Type A= 2mm – 4 wires, Type B: 1mm – 6 wires.

Repeated Loading for Type B specimens

• 2D actuators were fabricated using LTM217/Kevlar 29 prepregs. The thickness of each lamina was 125microns. The specimens were prepared with six prepreg layers, three on top and three on the bottom of the SMA wires that were placed in the middle of the thickness.

• A special frame – mould arrangement was used to hold wires in place while manufacturing in the autoclave.

• There have been various test carried out in the small scale specimens in order to assess mechanical performance and actuation behavior.

LTM217/kevlar

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2D smart skin • A smart skin that can deflect upwards to alter

aerodynamic properties was designed and tested. • The skin was made of MTM resin with 3 layers +

SMA +3 layers. 74 wires of D=0.2mm have been used. The plate is HxW =210x160 mm. The thickness of the patch was 0,7mm. The wires are wired in blocks of 5 (in parallel to make one group). The 14 groups of 5 and one of 4 SMA wires were connected in series. The total resistance of actuators to be heated Rtot=29 Ohm.

• Power requirements ~30W.

MTM44-1 epoxy SMA wires

Deflection

Basic Patch dimensions: LxD: (285 x 160)mm2, dSMA=0.3mm, Patch Thickness (tp)=1.5mm Wire Spacing (H) = 2.5mm

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Design with SMA – Modeling tools • The constitutive SMA model has been

implemented in ABAQUS commercial FEA code within the CleanSky project SMyLE.

• It is based on the model of D. Lagoudas2. and is accurate and can be implemented in FEA codes.

• This was implemented in ABAQUS by using the User material subroutine (UMAT). UMAT is a subroutine provided by ABAQUS in order to define a material’s mechanical behavior. The logical diagram of the UMAT subroutine is presented on top left.

• Good correlation between numerical predictions (red curves) and experimental data (blue curves).

• This design tool has proven valuable in conceptual and detailed structural design.

2. Lagoudas, Dimitris C, Shape Memory Alloys - Modeling and Engineering Applications

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Design with SMA – Modeling tools • It has been verified that the dynamic thermo-

mechanical behaviour of SMA actuator is quite complex characterized by severe non-linear phenomena, rendering the analytic modelling of an SMA actuator quite difficult in many practical applications.

• The objective of the proposed enhancement is to present a complete methodology for identifying the SMA actuator dynamics based, exclusively, on experimental measurements, without the need of analytic modelling.

• This is presently achieved through the Non linear Auto Regressive with eXogenous excitation (NARX) model class, which is able to capture the dynamical behaviour of a fairly wide range of non linear phenomena. Furthermore, the NARX model class may properly be extended to the Functionally Pooled NARX (FP-NARX) model class in order to capture different and/or varying operating conditions.

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Applications: Compliant Leading Edge

• The rib mechanism is called ‘Compliant Mechanism’ and it is designed to provide a targeted morphing airfoil shape utilizing NiTiNol SMA material. The desired airfoil leading edge displacement of the morphed shape with respect to the unmorphed is around 1.2 mm or 3° degrees in terms of rotation angle for a rib of 620mm chord-wise length.

• The structure has been modeled using the SMA thermo-mechanical element in ABAQUS FEA. • Technical feasibility and predictions validation was performed by testing at relevant conditions. • Good correlation between theoretical and experimental data.

Compliant Ribs CAD models FEA results

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Applications: Trailing edge morphing wing

• Geometric and aerodynamic specifications were provided.

• Based on these inputs the DESA architecture was designed and analyzed by in-house developed FEA modules that allow for accurate simulation of the shape memory effects. With the aid of these modules the static and dynamic behavior of the DESA architecture was modeled and critical design parameters evaluated.

• The output of this task will be 3D CAD models and design drawings that will be used for DESA manufacturing.

DESA prototype concept

Flap clean and morphed shapes.

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Flap pressure coefficient vs. norm. chord

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Applications: Trailing edge morphing wing • The solution incorporate two pivots per rib

which allow the airfoil to assure the correct morphed and un-morphed shapes with the actuation of the proper SMA side.

• The temperature of the SMA wire is increased by heating up an overbraided heating element rather than passing current through the SMA. In this way it is possible to use multiple wires and increase the excreted force without increasing with minimal power requirements. For the actuation of the DESA prototype 60W were enough.

• Four actuation sections were used. The overall dimensions were 0.8m cord x 1m span length.

Pivot

SMA actuators Overwrapped by heater

SMA actuators Overwrapped by heater

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Applications: Trailing edge morphing wing • The wing was tested in representative conditions

achieving TRL4. • The wing was evaluated against aerodynamic loads by

performing morphing and un-morphing cycles under full loading.

• The dynamic properties were also measured.

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Applications: Trailing edge morphing wing • All major objectives of project have been achieved. • DESA prototype designed, manufactured and tested . • Technical issues with the application of SMA actuators

have been successfully addressed. • Low power consumption (~60W), Electrical safety. • SMA characterisation and use of dedicated numerical

tools (dedicated FEA). • Stabilization of SMA thermo-mechanical behavior. • One publication produced (AIRTEC 2013).

• The works have been carried out within the framework of

Clean Sky SMyLE and SmyTE projects.

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Thank you for your attention

Contact details (to be added) For project information and details contact: Mr. Dimitri Karagiannis, INASCo d.karagiannis@inasco.com, +302109943427