Test Cases for Modeling and Validation of Structures with Piezoelectric Actuators

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 (3x1.75)
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 _at_ 31.8 Hz
Mode 1 _at_ 5.06 Hz
Mode 3 _at_ 57.6 Hz
Mode 4 _at_ 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
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