1. DEVELOPMENT OF A SIMPLE MORPHING WING USING ELASTOMERIC COMPOSITES AS SKINS AND ACTUATORS
Larry D. Peel, PhD, PE
James Mejia (recent graduate)
Ben Narvaez (recent graduate)
Kyle Thompson (recent graduate)
Madhuri Lingala (graduate student)
Department of Mechanical and Industrial Engineering
Texas A&M University - Kingsville
Oct. 29, 2008

2. Why Fiber-Reinforced Elastomer Composites?
Advantages of Fiber-Reinforced Elastomer (FRE) Composites
High Impact Strength, paper,
Vibration damping, paper,
Extreme (High & Auxetic) Poisson’s Ratios, papers
Tailorable (Tunable) nonlinear response in deformation and stiffness, paper,
Applications
Utility Poles, vibration dampeners, biomimetics, actuators, sensors, morphing aircraft structures.
Flexible underwater vehicles, Inflatable space structures
Papers at users.tamuk.edu/kfldp00/

3. Selected Previous Works
Lockheed Martin Z-wing – Hinged, rigid internal structure, covered with reinforced silicone rubber skin, initially Shape Memory Polymer skin.
FlexSys – Developed Mission Adaptive Compliant Wing, nose deflects downward 6º, trailing edge deflects 10º.
Kikuta outlines a number of requirements – Tailored flexibility, toughness, abrasion and chemical resistant, high elastic strain capability & recovery….
Thill et. Al. note the high strain capability of elastomer skins is useful but “difficult to design elastomeric skins that can sustain & transfer load…”
Thill et. Al. note auxetic skins could have high energy absorption, fracture toughness…. Synclastic behavior.
Peel has experimentally obtained FRE Poisson’s ratios up to 21> n > -5, predicted 100 > n > -60.
Rathnam & Peel showed high impact resistance of FRE laminates.
Keshavamurthy, Hossakere, Peel show high damping from Auxetic & high Poisson’s Ration Laminates.
Klute, Hannaford, Peel, Hossain, Bakis, have fabricated McKibben-like actuators.

4. First Generation Morphing Wing student project
Fiber/elastomer morphing wing, with high force actuators, designed, fabricated, tested in a 2-week “Maymester” by Peel, Krystal Gunter, & Royce Coons.
Each 0.5 in. rubber muscle actuator produced 200 lbs, 34X pneumatic, at 30 psi.
Crude FEA model, actual wing tip & tail deflect down 20º at 30 psi.

5. First Generation Morphing Wing Data
Upper molded wing skin is [±10º]s carbon fiber / RP6444 laminate.
RP6444 – polyurethane, 60D, 300% elongation, ore-hauling trucks.
Lower skin – [90º]n carbon / RP6442 (80A), more compliant - buckled.
Rigid carbon/epoxy wing box. Skins attached with wood screws.
Total materials cost less than $300, but used filament winder, lab.
Good proof of concept, lower wing skin buckled, wrinkles in upper skin, non-aerospace fasteners, actuators got pinhole leaks.

6. Second Generation Wing Development
Senior Design Project - 9 mon.
Objectives
Fit in suitcase to demo, no buckling or wrinkling, high rigidity, smooth bending.
Specs
Clark Y airfoil
Upper skin 1-piece molded, same carbon/RP6444, piano hinges bonded to wing box.
Lower wing skin same layup as upper, thinner.
Lower skins slide on guides.
Improved actuator force & attachments.
Much higher quality fabrication.

7. Rubber Muscle Actuator (RMA) Development
Filament wound
Filament wound
Braided sheath
Braided sheath
All RMA’s carbon/RP6410 wound or braided at [±10º]s for higher forces.
Filament wound RMAs developed pinhole leaks, hard to maintain fiber spacing, used metal inserts & clamps/ wire. Good force output.

8. Functionally Gradient Rubber Muscle Actuators
Needed new attachment method, first Functionally Grad muscles filament wound, left dry fiber that was post-cured with semi-rigid resin & cloth.
Braided sheaths from A&P Technologies faster, better, no metal parts.
Actuator region is compliant polyurethane, attachment area is rigid polyurethane, carbon fiber used to “clamp” plastic fittings. Quite robust.

9. RMA Force vs Pressure & Contraction
Basic McKibben model used to predict Force vs Pressure for 0.5 in dia RMAs.
Braided muscle –higher forces, both needed minimum pressure to ‘activate’.
Braided RMAs with same diameter contracted more, higher forces.
“Blocked” actuators (pre-stressed, return or stretching) produced higher forces.
More details on A&P & our work in SAMPE 09 paper.

10. Finite Element Modeling
Response of FEA model with sliding contact elements matches fabricated wing.
Equivalent inplane auxetic upper skin showed no appreciable difference in deformation.
Fabricated wing and FEA model will complement each other for future work and characterization.

11. Auxetic Skins?
In-plane auxetic or thickness-direction auxetic behavior?
Experimentally obtained inplane Poisson’s ratios 21> n > -5, predicted 100 > n > -60.
Current skins are likely already auxetic in thickness direction.
Thill et. Al. note auxetic skins could have high energy absorption, fracture toughness…. Synclastic behavior.

12. Conclusions
Both wings show excellent angles of deflection, and the Generation II wing shows no buckling or wrinkling of its wing skins.
A series of Rubber Muscle Actuators were refined.
The latest braided actuators have functionally gradient properties, produce higher forces than similar filament wound actuators and have not developed air leaks.
Fiber-reinforced elastomers have enabled the extremely tough morphing wing skins, their internal actuators and can enable auxetic behavior if needed.
Future Work
Actuate nose & tail separately.
Characterize control, aerodynamics.
Replace fasteners with aerospace ‘Clikbond’ type fasteners.
Replace elastomeric matrix with Shape Memory Polymer Matrix & characterize.
Develop compliant mechanism truss-like configurations, explore thickness & inplane auxetic skins.

13. Acknowledgement The authors wish to thank:
A&P Technologies for the braided sheaths;
Victor DeLeon for all his great machine work;
Krystal Gunter and Royce Coons for their preliminary Maymester work;
the MEEN 4263/64 Senior Design class for their constructive feedback; also,
Juan Rangel for his formatting and Excel plotting expertise;
Larry’s wife, for supporting his “Elastomer Composites / Auxetics habit”

14. Thank you……. Questions?

15. References
Lawlow, M., Oct. 2006, “The Shape of Wings to Come,” SIGNAL [online journal],
Thill, C.l, Etches, J., Bond, I., Potter, K. and Weaver, P., 2008, “Morphing Skins,” The Aeronautical Journal, No
FlexSys,
Skillen, M.D., and Crossley, W.A., 2007, “Modeling and Optimization for Morphing Wing Concept Generation,” NASA/CR
Kikuta, M.T., 2003, “Mechanical Properties of candidate materials for Morphing Wings,” Dept. of Mech. Engr, Virginia Tech, p. 123.
Alderson, K.L., et. al., 2005, “How to Make Auxetic Fibre Reinforced Composites,” Wiley-VCH, Poznan-Bedlevo, Poland.
Peel, L.D., Sep. 2006, “Experimental Results of High and Negative Poisson's Ratio Elastomer-Matrix Laminates,” 3rd Workshop on Auxetics & Related Systems, Exeter, UK, presentation.
Peel, L.D. , 2007, “Exploration of High and Negative Poisson’s Ratio Elastomer-Matrix Laminates,” J. Physica Status Solidi (b) 244, No. 3, 988–1003.
Peel, L.D., Dec. 1998, Fabrication and Mechanics of Fiber-Reinforced Elastomers, Ph.D. dissertation, Brigham Young University, Provo, UT.
Rathnam, K.V. and Peel, L.D., May 2004, “Impact Resistant Fiber-Reinforced Elastomer Composite Materials,” SAMPE 2004, Long Beach CA.
Keshavamurthy, D., Hossakere, K., Peel, L.D. , May 2005, “Vibration Damping Using High and Negative Poisson's Ratio Laminates,” SAMPE 2005, Long Beach CA.
C.P. Chou, B. Hannaford, Feb. 1996, 'Measurement and Modeling of McKibben Pneumatic Artificial Muscles,' IEEE Transactions on Robotics and Automation, vol. 12, pp
Klute, G.K., Hannaford, B., June 2000, 'Accounting for Elastic Energy Storage in McKibben Artificial Muscle Actuators,' ASME Journal of Dynamic Systems, Measurements, and Control, vol. 122, pp
Klute, G.K., B. Hannaford, B., Nov. 1998, 'Fatigue Characteristics of McKibben Artificial Muscle Actuators,' IROS-98 Proceedings, pp , Victoria, B.C., Canada.
Hossain, M. Z. , May 2003, “Linear Finite Element Analysis of a Rubber Muscle Actuator,” Masters Report, Texas A&M University – Kingsville, Kingsville, TX.
Shan, Y., and Bakis, C.E., “Flexible Matrix Composite Actuators,” 20th Annual Technical Conference of American Society for Composites, Sep., 2005, Philadelphia, PA.
Peel, L.D., Gunter, K., Coons, R., May 2006, “Morphing a Wing,” Maymester Program, Texas A&M University – Kingsville, Kingsville, TX, departments/ieen/faculty/DrLPeel/maymester_wing_warp.htm
Peel, L.D., Mejia, J., Thompson, K., Narvaez, B., Dec. 2007, “Morphing Wing Senior Design Presentation,” Texas A&M University – Kingsville, Kingsville, TX.
Shadow Robotics, “Technical Specification,”
Heracovitch, C.T., 1984, “Composite Laminates with Negative Through-the-Thickness Poisson’s Ratios,” Journal of Composite Materials, vol. 18, pp