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Dynamic Investigations
The dynamic parameters of the CFRP specimen were investigated under different conditions:
Support
− freely suspended
− on defined springs
− soft foam
Excitation
− impulse hammer
− electrodynamic shaker (Brüel&Kjaer 4809)
− HP CFP modules of NMW
Type of Excitation
− impulse
− sweep 2500 ¸ 4000 Hz
− band-limited noise 2000 ¸ 5000 Hz
Sensor System
− scanning laser doppler vibrometer
− piezoelectric accelerometer
Scanning Laser Doppler Vibrometer Polytec PSV 400 with CFRP specimen
Excitation
Band-limited noise by electrodynamic shaker. 2000 Hz to 5000 Hz
Summary
Test series | Noise | Impulse excitation | Exciter Sweep | Discrete Sinus |
Suspension | free-free (see | free-free (see | free-free (see figure 85) | on springs (see figure 87) |
Sensor | laser vibrometer | piezoelectric acceleration sensor | laser vibrometer | |
Excitation | band-limeted noise, electrodynamic shaker, 2000 Hz to 5000 Hz | impulse with EMA hammer and wrench | sweep, electro-dynamic shaker, 2000 Hz to 5000 Hz | discrete sinus at eigenfrequency, PZT actuator, dying-down |
Determined parameters | eigenfrequencies, mode shapes | D ≈ 1 to 2 % of critical damping | D ≈ 3 % of critical damping | D ≈ 0,4 to 1 % of critical damping |
- measured natural frequencies (and mode shapes) match simulation
- damping with impulse excitation (low amplitudes) D = 1 ¸ 2 % of critical damping
- damping with vibration exciter D » 3 % of critical damping
- laser vibrometer measurements with discrete sinuas: D = 0,4 ¸ 1 of critical damping
Beams and Composites with PZT sensors and actuators for active control
In many industrial and defence applications, noise and vibration are important problems. Over the past years, control of sound and vibration has been and still is subject of extensive research work, and examples of applications are now numerous. The three most common classifications of vibration control are:
· passive
· active
· hybrid control
Passive control involves the use of reactive or resistive devices that either load the transmission path of the disturbing vibration or absorb vibration energy. Active control also loads the transmission path, but by the use of actuators that generally require external energy counteracting forces are applied. Hybrid control integrates passive approach with an active control structure. For hybrid control it is necessary to investigate composite materials together with sensors and actuators. The following beams were available and investigated:
6.2.1 Beam 1: Aluminium – PZT Plate
6.2.2 Beam 2: Aluminium – PZT Plate
6.2.3 Beam 3: GFRP – HP-PFC
6.2.4 Beam 4: GFPR – HP-PFC
6.2.5 Beam 5: CFPR – HP-PFC
For further details with regard to the beams investigated, please see Attachment 1