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Test Cases for Modeling and Validation of Structures with Piezoelectric Actuators

Test Cases for Modeling and Validation of Structures with Piezoelectric Actuators. Mercedes C. Reaves and Lucas G. Horta Structural Dynamics Branch NASA Langley Research Center Hampton, Virginia Presented at the NASA Innovative Finite Element Solutions to Challenging Problems Workshop

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Test Cases for Modeling and Validation of Structures with Piezoelectric Actuators

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  1. Test Cases for Modeling and Validation of Structures with Piezoelectric Actuators Mercedes C. Reaves and Lucas G. Horta Structural Dynamics Branch NASA Langley Research Center Hampton, Virginia Presented at the NASA Innovative Finite Element Solutions to Challenging Problems Workshop May 18, 2000 at NASA GSFC

  2. Outline • Objectives and background • Approach • Modeling methods • Aluminum beam testbed description/results • Composite beam testbed description/results • Concluding remarks

  3. Objective Investigate and validate techniques for modeling structures with surface bonded piezoelectric actuators using commercially available FEM codes.

  4. Approach • Develop and validate FEM models of the following structures: • Aluminum beam testbed • Composite beam testbed • Study the following piezoelectric modeling approaches: • Piezoelectric effect via thermal analogy and Ritz vectors • Piezoelectric element using NASTRAN dummy element capability • ANSYS piezoelectric element

  5. Modeling Approaches • Thermal Strain Analogy • Induced strain using thermal load • 4-node composite quadrilateral element • Ritz vectors computed to capture local effect • MRJ piezoelectric elements implemented in User-Modifiable MSC/NASTRAN • Piezoelectric induced strains • Coupled field 4-node composite quadrilateral element • ANSYS • 3-D Coupled Field Solid element • Full harmonic analysis

  6. Aluminum Beam Testbed Aluminum Beam LaRC Piezoelectric Actuator

  7. Aluminum Beam Testbed Actuator (3”x1.75”) Strain gage 2.78” 3.625” 16” Actuator 0.04” Back to Back Strain gages

  8. Instrumented Aluminum Beam Two strains gages mounted back to back Strain gages and Actuator Proximity Probe

  9. Aluminum Beam Analysis Results Mode 2 @ 31.8 Hz Mode 1 @ 5.06 Hz Mode 3 @ 57.6 Hz Mode 4 @ 89.4 Hz

  10. Composite Box Beam Testbed PZT actuator 0.5” Strain gage 3.0” PZT actuators 66 “ Beam cross section (Outside dimensions) 0.75 ” 3.0 ” laminate thickness = 0.03” Material T300/976 laminate layout [45,-45,0] s

  11. AL Beam Correlation from Various Analysis Codes Strain measurements versus Analysis Correlation -5 10 Strain in/in/volt MRJ Ritz Test v-bond ANSYS -10 10 -1 0 1 2 3 10 10 10 10 10 Frequency (Hz) 200 100 Phase (Degree) 0 -100 -200 -1 0 1 2 3 10 10 10 10 10 Frequency (Hz)

  12. AL Beam Correlation from Various Analysis Codes Out of Plane Displacement Measurement versus Analysis Correlation 0 10 Tip Displacement in/volt -5 10 MRJ-e116 Ritz-e116 Test v-bond ANSYS -10 10 -1 0 1 2 3 10 10 10 10 10 Frequency (Hz) 600 400 Phase (Degree) 200 0 -200 -1 0 1 2 3 10 10 10 10 10 Frequency (Hz)

  13. Results from Thermal Mapping Test on AL Beam Possible disbonds Thermal mapping image of actuator bonded to the aluminum beam

  14. Bonding Technique v-bond- 14.5 psi, 24 hrs cure, vacuum bag p-bond- 1 psi, 24 hrs cure, ambient Comparison of Actuator Effectiveness on AL Beam Strain Measurements -5 10 Strain in/in/volt Test p-bond Test v-bond -10 10 -1 0 1 2 3 10 10 10 10 10 Frequency (Hz) Displacement Measurements 0 10 Test p-bond Test v-bond Tip Displacement in/volt -5 10 -10 10 -1 0 1 2 3 10 10 10 10 10 Frequency (Hz)

  15. Instrumented Composite Box Beam Testbed Proximity Probe Beam Strain Gage Actuators

  16. Composite Box Beam Analysis Results 11.1 Hz 68.9 Hz 186.7 Hz 279.6 Hz

  17. Box Beam Test versus Analysis Correlation Strain measurements versus Analysis Correlation -5 10 Analysis Test -6 10 Strain in/in/volt -7 10 -8 10 -1 0 1 2 3 10 10 10 10 10 Frequency (Hz) 200 100 Phase (Degree) 0 -100 -200 -1 0 1 2 3 10 10 10 10 10 Frequency (Hz)

  18. Box Beam Test versus Analysis Correlation Out of Plane Displacement Measurement versus Analysis Correlation -2 10 Analysis Test -4 10 Tip Displacement in/volt -6 10 -8 10 -1 0 1 2 3 10 10 10 10 10 Frequency (Hz) 600 400 Phase (Degree) 200 0 -200 -1 0 1 2 3 10 10 10 10 10 Frequency (Hz)

  19. Concluding Remarks • Two testbeds developed and tested for validation of commercial analysis tools • Frequency response functions results using three different analysis approaches provided comparable test/analysis correlation • Low frequency resonance predicted within 5 and 13% but antiresonance showed errors of 16% • Improper bonding of actuators showed reductions in electrical to mechanical effectiveness of 64 %

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