Characterizing the Dynamic Properties of Laminated Composites with Embedded Electro-Viscoelastic Materials by John Kosmatka Department of Structural Engineering University of California San Diego, CA 92093 (858) 534-1779, jkosmatka@ucsd.edu http://casl.ucsd.edu/ Presented at: 2003 CompTest Meeting Châlons-en-Champagne, France January 28-30, 2003 2003 CompTest Meeting

Experimental Development Validation Experimental Studies Conclusions Overview Background Introduction Experimental Development Validation Experimental Studies Conclusions January 28-30, 2003 2003 CompTest Meeting

Background NASA-Glenn/UCSD Damped Fan Blades Currently: Goal: Blades are designed to have minimal vibration response in operating speed range Start-up and varying engine speeds can produce resonant response (fatigue) Reduce blade fatigue in first chord-wise (two-stripe) mode 1/5 scale Titanium Graphite/Epoxy [(±45)2/0/45/0/-45/0/45/0] [04] [0/45/0/-45/0/45/0/(±45)2] Goal: Reduce response as one passes through resonances during engine start-up Eliminate (reduce) blade bending-torsion flutter during operation January 28-30, 2003 2003 CompTest Meeting

Background NASA-Glenn/UCSD Damped Fan Blades Design & Analysis Finite element modeling of spinning blade Modal Strain Energy Method - Chord Mode Max Strain and Hashin Failure Criteria, B-Basis Composite Properties (6 specimens) Maximum (9% volume) Optimum (4% volume) Two Center Ply Designs VEM TEDLAR Open Mesh VEM Patch Barrier Film: (0.0025 mm) TEDLAR VEM: (0.05 mm) Avery 1125 Glass Open Mesh Weave January 28-30, 2003 2003 CompTest Meeting

Background NASA-Glenn/UCSD Damped Fan Blades Testing Vacuum Spinning (NASA-Glenn) Hub Magnetic Bearing Excitation Strain Gauge Response Accelerometer Response Measure strains at: (1x, 2x, 4x, 6x, 8x 10,000 rpm) Damping Levels are: 2x (optimal damped), 8x (maximum damped) 2,500,000 Cycles on Blades No Delamination Observed January 28-30, 2003 2003 CompTest Meeting

Background Viscoelastic damping material limitations: Narrow Frequency Range Multiple materials are needed for wide frequency range Temperature Sensitive Multiple materials are needed for wide temperature range Reduces resonance response, but increases off-resonance response Good engineering designs (vibration isolation) are penalized and can have greater response January 28-30, 2003 2003 CompTest Meeting

Background What is needed: Damping materials where the damping levels can be varied and controlled High damping when excitation (engine harmonics) are close to resonance Low damping when excitation (engine harmonics) are not close to blade resonance Completely passive system Sensor and computer embedded in blade root Sense blade response and change damping levels accordingly Damper and computer power comes from eddy current (magnets on spinning blades) January 28-30, 2003 2003 CompTest Meeting

Introduction EVEM: Electro-Viscoelastic Materials EVEM Mechanism Develop damping materials whose stiffness and damping properties can be tuned with voltage Electro-rheological and magneto-rheological fluids are adjustable dampers (material is not self-supporting or sealed) Microscope Photo EVEM Mechanism A polarizable polymer powder is dispersed in a silicone gel. Application of voltage causes attraction that stiffens polymer. + _ Silicone gel Polarizable particles Apply voltage January 28-30, 2003 2003 CompTest Meeting

Develop Tunable Dampers Introduction Electro-Viscoelastic Materials: Property Range EVEM Frequency Dependent Temperature Dependent Strain Magnitude Dependent Electric Field Dependent Damping Materials EVEM Composites Rubbers Polymers Develop Tunable Dampers Metals Modulus (Msi, 6900 MPa) January 28-30, 2003 2003 CompTest Meeting

Equipment Development System Overview Put specimen in pure shear Harmonic Excitation Vary voltage and temperature Test Fixture Shaker Amplifier Computer PSV-Controller Data Acquisition Signal Conditioner Velocity Signal Force Signal Amplified Signal Drive Signal Conditioned Force Signal DC Voltage Supply VDC Refrigerated Circulator System Double-Lap Shear Laser Vibrometer January 28-30, 2003 2003 CompTest Meeting

Equipment Development Test Fixture Layout Double Lap Shear Test Fixture Direct Force/Stress Measurement Produces Pure Shear Minimizes Transverse Effects MB Modal 50 Shaker Frequency Range: DC to 5000Hz 250 N Peak Force Force Transducer 50 N, 250 N, or 500 N Nylon Insulator/Coupler Force Transducer Outer Block Nylon Coupler Center Block Electroviscoelastic Material Specimen Stinger Shaker January 28-30, 2003 2003 CompTest Meeting

Electrical System Setup and Isolation Equipment Development Ground Inner Copper Plate Outer Copper Plate Center Block EVEMs -VDC GND Electrical System Setup and Isolation Voltage from 0 to -1500 Volts Negative Voltage Applied to Electrodes bonded to Center Block Electrodes bonded to Outer Blocks are Grounded Force Transducer Insulated by Nylon Coupler Phenolic Washer and Spacers for Insulation Shrink Wrap Tubing on Bolts for Insulation Outer Block Base Plate Phenolic Washer and Spacer Shrink Wrap Tubing Nut Bolt January 28-30, 2003 2003 CompTest Meeting

Equipment Development Heat Exchanger System Polyscience Refrigerated Circulator System Uses Liquid Convection Temp Range from -25°C to 100°C Test Fixture Encased in Sealed Plexi-Glass Box Filled with N2 to Prevent Condensation at Low Temps January 28-30, 2003 2003 CompTest Meeting

PSV-Laser Vibrometer System Equipment Development PSV-Laser Vibrometer System Measure velocity of moving and stationary blocks Based on Laser Interferometry and Doppler Effect Non-contacting Vibration Measurement System Includes: Multi-point Scanning Laser Laser Controller Video System Built-in Function Generator 3-channel Data Acquisition System January 28-30, 2003 2003 CompTest Meeting

Calculation of Dynamic Properties Material Property Determination Calculation of Dynamic Properties Specimen (G2*,m2) X2 Stationary Block t2 X Moving Block (M) F(t), Input Force X1 Stationary Block t1 Specimen (G1*,m1) Equation of motion in terms of block displacements: Assuming specimens have equal properties with (G* = GR + iGI): January 28-30, 2003 2003 CompTest Meeting

Material Property Determination Assume harmonic force: Velocities are given by: The displacements and accelerations are: Substituting in previous equations and multiplying by iw: January 28-30, 2003 2003 CompTest Meeting

Material Property Determination Putting in matrix form and solving for GR and GI as a function of (w): Loss Factor as a function of (w) can be calculated by: January 28-30, 2003 2003 CompTest Meeting

Experimental Results Validation EVEM Studies Avery 1125 Specimen Preparation Silicone Gel Only – Voltage and Temperature EVEM – Voltage Effects EVEM – Voltage and Temperature Effects January 28-30, 2003 2003 CompTest Meeting

Experimental Results System Validation Using a Commercial VEM Avery 1125 VEM Test Performed at Several Temperatures Use Reduced Frequencies and Temperature Shifts Curves Overlay Tightly January 28-30, 2003 2003 CompTest Meeting

Experimental Results EVEM Specimen Preparation Base Gel: (50-90%) Dow Corning 527 Silicone Dielectric Gel (10-50%) Dow Corning Sylgard® 182 Silicone Elastomer (stiffener) P-Polyphenyl Particles (PPP): Synthesized by coupling benzene using aluminum chloride and cupric chloride Doped with FeCl3 by suspending in ethanol and anhydrous FeCl3 at 60oC for 24 hrs. Cure under vacuum between copper skins with 1kV to align particles Specimen bonded to test fixture with cyanacrylate adhesive tEVEM = 0.635mm 12.7 mm 38 mm tCu = 0.76 mm Microscope Photo January 28-30, 2003 2003 CompTest Meeting

Experimental Results Gel Only: 100% Dow Corning Sylgard® 182 Silicone Elastomer (stiffener) No Voltage Effect -20oC, 0-2KV -4oC, 0-2KV 21oC, 0-2KV Shear Modulus, GR (psi = 6900 Pa) 60oC, 0-2KV January 28-30, 2003 2003 CompTest Meeting

Experimental Results 20% PPP 80% Gel: 80% Dow Corning 527 Silicone Dielectric Gel 20% Dow Corning Sylgard® 182 Silicone Elastomer (stiffener) Shear Modulus, GR (psi = 6900 Pa) Shear modulus increases (600%) and damping decreases (60%) with voltage (1.5KV), attracting particles increase required shear force January 28-30, 2003 2003 CompTest Meeting

Experimental Results 10% PPP 90% Gel: 80% Dow Corning 527 Silicone Dielectric Gel 20% Dow Corning Sylgard® 182 Silicone Elastomer (stiffener) Apply 1.5 KV -15oC 21oC -15oC Shear Modulus, GR (psi = 6900 Pa) 2oC 55oC 2oC 21oC 55oC January 28-30, 2003 2003 CompTest Meeting

Conclusions Test system validated with commercial VEM Electrical isolation techniques successful Test apparatus is able to accurately characterize EVEM properties. For the material tested: Large increases (600%) in shear stiffness are observed as a function of voltage. These increases are greater at lower temperatures Large decreases (60%) is damping (loss factor) are observed as a function of voltage. These decreases are greatest between freezing and room temperature January 28-30, 2003 2003 CompTest Meeting