Healable, Shape Memory Polymers for Reflexive Composites Thomas Barnell Research Engineer This work was funded under a NASA SBIR, Contract number NNL06AA07C from NASA Langley. barnelltj@crgrp.com (937) 320-1877 x 164
Presentation Outline Technology Overview Project Objectives Reflexive Structures Applications Material Development Healing Concept Healable Shape Memory Polymers (SMP) Experiments and Results Neat Resin Testing Carbon Fiber Reinforced (CFR) Composite Testing Future Work Formulation Optimization Testing
Program Goals and Objectives Program Goal Develop & demonstrate autonomous damage sensing & repairing of composite aircraft structures Technical Objectives Develop discrete heating system Integration of sensor & heating system Optimize healable SMP resins Develop autonomous control system Characterize performance Commercialize healing SMP resins through CRG Industries Commercialize reflexive composite systems through CRG Inc.
Damage Occurs Damage Detected Damage Reported Healing Reported Damage Healed Damage Healing
Reflexive Structures Structural Health Monitoring (SHM): Sensing layer piezoelectric ceramics Active sensing compare damage data to baseline (healthy) data Intelligent Structural Control System: Damage prioritization size, location, magnitude, etc. Healing implementation time, power, temperature Discrete healing co-cured foil Kapton heater Healable Shape Memory Polymer Recover form Shape memory effect Recover performance Polymer chain diffusion Damaged 2 Min. healing 5 Min. healing
Reflexive Structures Benefits: Increased survivability Decreased maintenance Weight savings reduced damage tolerance Implement SHM, healable material, or both Industries Aerospace Wing skins, Structural components Automotive Panels Energy Wind turbine blades Infrastructure Bridge decking Previous Work Microencapsulation White Microvascular Sottos Reversible reaction Wudl Thermoplastic additive Hayes
Healable Shape Memory Polymer Dual Healing Mechanisms: Shape memory effect Reptation model (de Gennes) Break Time Ends move Centers move Centers on break Estimated elapsed time t = 0.05 Sec
Healable Shape Memory Polymers Materials: Styrene-based SMP modification of Veriflex Materials: Styrene SMP A Styrene SMP B Formulation method: Incorporation of thermoplastics in thermoset matrix Epoxy-based SMP modification of Veriflex E Materials: Epoxy SMP A Epoxy SMP B Formulation method: Increase thermoplastic character of material via reactive additives Chemical Crosslink Free Chain
Neat Resin Testing SMP properties Styrene SMP A and Epoxy SMP A T g s are tailorable for specific applications Glass transition, T g ( C) Tensile Elongation (%)* Tensile Modulus (Mpa)* Styrene SMP A 90 190.0 1.50 Epoxy SMP A 62 268.8 0.66 * tested at 30 C above T g Tensile and Flexural Properties Styrene SMP A and Epoxy SMP A Baseline: EPON 826 / EPI-CURE 9551 Strength (Mpa) Modulus (Gpa) Deformation (%) Tensile (ASTM D638) Styrene SMP A 26 2.4 1.4 Epoxy SMP A 71 3.0 3.5 Epon 826 69 2.5 10.6 Flexural (ASTM D790) Epoxy SMP A 119 3.6 -- Epon 826 117 2.8 --
Neat Resin Testing Neat healing test Epoxy SMP A ASTM D5045: Plane-strain fracture toughness and strain energy release rate of plastic materials Single edge notch bend (SENB) test Specimens taken to complete failure Healed at 92 C for one hour 10000 400 Re-tested Storage Modulus 350 Loss Modulus Values reported: 300 1000 Maximum load 250 Stress intensity factor (K I c) 200 Energy release rate (G I c) 100 Storage Modulus (MPa) 10 150 100 50 Loss Modulus (MPa) 0 1-50 25 50 75 100 Temperature ('C) DMA of Epoxy SMP A UTM Test setup
Neat Resin Testing Epoxy SMP A results Maximum Load 80% recovery Stress intensity factor, K I c 66% Strain energy release rate, G I c 37% Average of test specimens (>3x) healing percentages 2.5 160 KIc (MPa*m^0.5), GIc (kj/m^2)_ 2 1.5 1 0.5 0 Before Damage KIc (Mpa-m1/2) GIc (kj/m2) Max load (N) 140 120 100 80 60 Max Load (N) 40 20 ASTM D5045, SENB 0 After Healing
Composite Testing Composite healing test ASTM D790: Flexural properties of unreinforced and reinforced plastics and electrical insulating materials (3-point bend) Composites: 12 ply 3k plain weave [0,90] carbon fabric Styrene SMP A and B, Epoxy SMP A and B, Baseline (EPON 826/EPI-CURE 9551) VARTM infused One specimen of each material taken to complete failure max stress noted Other specimens taken to 110% deformation at max stress induce matrix failure Suspended in oven and healed at 30 C above T g Re-tested for one hour ASTM D790 Specimens after initial failure and subsequent healing
Composite Testing 800 Flexural Strength Recovery: 700 Styrene SMP A 89% Styrene SMP B 85% Epoxy SMP A 78% Epoxy SMP B 85% Flexural Strength (MPa) 600 500 400 300 200 Styrene SMP A Styrene SMP B Epoxy SMP A Epoxy SMP B Epon 826 Epon 826 / Epi-cure 9551 57% No recovery of form 100 0 Before Damage After Healing 40 35 Flexural Modulus Recovery: Flexural Modulus (GPa) 30 25 20 15 10 Styrene SMP A Styrene SMP B Epoxy SMP A Epoxy SMP B Epon 826 Styrene SMP A 93% Styrene SMP B 88% Epoxy SMP A 80% Epoxy SMP B 78% 5 Epon 826 / Epi-cure 9551 57% 0 Before Damage After Healing
Summary Healing performance: Rapid, simple, and repeatable healing mechanism Epoxy SMP A offers superior combination of healing and performance Restores shape and mechanical performance Future work (resin system): Neat healing testing on baseline Resin reformulation based on results Marine compatible resin system Fiber/matrix interface investigation Further healing testing Different times and temperatures Repeated healing cycles Compression after impact (CAI)
Acknowledgements NASA Langley: Mark Cagle CRG: Sam Knutson Chris Jensen