Download AF083-264

AF083-264
TITLE: MOBILE LOW-POWER MULTIPOINT LASER DOPPLER
VIBROMETER
TECHNOLOGY AREAS: Sensors
OBJECTIVE: Research and develop an alternative mobile, low-power, human eye safe, matrix laser beam
Doppler vibrometer.
DESCRIPTION: Vibration diagnostics and predictive structural health analysis plays an important role in
the flight testing of airframe structures and avionic sub-systems. AFFTC has a need to test structural
integrity and predictive response/failure analysis of control surfaces, relative response of doors, storehangers, articulating surfaces, pods, and fins.
The predictive analysis of structural-behavior to airflow, propulsion, ionic gases, shock waves, in low/high
atmosphere, under normal or extreme operating conditions, provides a key metric for evaluating design
integrity and structural health of flying vehicle and its avionics. It links actual system behavior to design
specifications.
Measurements of structural response to forced excitation are traditionally obtained from a distributed
network of surface mounted accelerometer load cells, which are time consuming to set up and dismantle.
More recently, there have been some publications in alternative methods, employing non-contact optical
measurements made possible by the laser Doppler vibrometer (LDV). It measures vibration at the point
where the laser beam is incident on the surface. The instrument is, however, costly (typ. $250,000), and the
measurement cycle can still be very time consuming on large structures which require many hundreds of
point measurements. With existing LDV instruments, this information must be inferred from multiple
time-sequential measurements based on the assumption that steady-state conditions prevail between the
first and final measurement.
The research is needed to devise an alternative low power human eye safe Multiple Beam Laser Doppler
Vibrometer to facilitate the single-shot capability of simultaneous measurement of structural integrity of
airframe structures. Electro-optic, acoustic, or multi-channel diffraction optics are preferred to be used to
achieve the multipoint measurement capability (2-D matrix including at least 256 points) without any
moving parts. This will also ensure minimum power consumption and eye safety. Other approaches which
offer the capability of providing these measurements without extensive use of accelerometers will also be
given appropriate consideration. Other factors that can be considered are developing an intelligent data
processing system that can process the measurement data and plot the whole field, time resolved vibration
data into engineering parameters commonly used in test, evaluation and design.
PHASE I: Perform a feasibility study and develop a conceptual design for mobile low-power multipoint
laser Doppler vibrometer.
PHASE II: Develop and demonstrate a prototype system based on the Phase I design.
PHASE III / DUAL USE: Military application: There exists a continuing need to measure and evaluate the
response to vibrations in military aircraft and components which could be greatly improved by new non
contact measurement technology. Commercial application: There exists a continuing need to measure and
evaluate the response to vibrations in civilian aircraft and components which could be greatly improved by
new non contact measurement technology.
REFERENCES:
1. A. Chattopadhyay, M. J. Schulz, R. Thornburgh, K. Waldron and A. Ghoshal “Experimental of Damage
Detection in Composite Material Structures Using a Laser Vibrometer and Piezoelectric Actuators” Journal
of Intelligent Material Systems and Structures, Vol. 14, No. 8, 521-537 (2003).
2. E. Peter Carden and Paul Fanning, Vibration Based Condition Monitoring: A Review, Structural Health
Monitoring, Vol. 3, No. 4, 355-377 (2004).
3. JA Oliver and JB Kosmatka , “Evaluation of modal-based damage detection techniques for composite
aircraft sandwich structures”, Proceedings of SPIE,Volume 5767, Nondestructive Evaluation and Health
Monitoring of Aerospace Materials, Composites, and Civil Infrastructure IV, May 2005, pp. 264-273.
4. Damage identification and health monitoring of Structural and mechanical systems from changes in
their vibration characteristics: A literature review. S. W. Doebling, C. R. Farrar, M. B. Prime, and D. W.
Shevitz. Technical Report LA-13070-MS, Los Alamos National Laboratory, Los Alamos, NM, 1996.
5. Cawley, P. et al. “The Location of Defects in Structures from Measurements of Natural Frequencies,”
Journal of Strain Analysis, Vol.14, No.2, p.49-56, 1979.
KEYWORDS: Matrix Laser Beam Doppler Vibrometer, control surfaces, relative response of doors, storehangers, articulating surfaces, pods, fins