262 / 352
258
A review of laser vibrometer types and their applications is given in Table 3.
Figure 20: The principle of an electronic speckle pattern interferometry (ESPI system /22/
Table 3: Laser vibrometers and their applications
Vibrometer type
The application
Standard Optic Vibrometers:
Standard optics high sensitivity single point vibrometers
Fiberoptic Vibrometers
Single point, differential and dual channel fiberoptic vibrometers
Scanning Vibrometers
For full field vibration measurements
Rotational Vibrometers
For angular vibration measurements on rotating structures
In-Plane Vibrometers
For 1-D in-plane vibration measurements
Production Vibrometers
Ruggidized industrial type compact vibrometer sensors
3D Vibrometer
For single point simultaneous X,Y and Z measurements
Compact Vibrometers
Compact high sensitivity vibrometers
Digital Vibrometers
Optimized digital decoding techniques for theoretical limit
performance and traceable calibrations
Portable Digital Vibrometers
Portable& affordable
High Speed Vibrometers
For measurements at high vibrational velocities
The examples of ESPI laser interferometry typical results are given in Fig. 21.
Vibration demonstration is typically for loud speaker, different figures can be obser-
ved according to the eigen modes, frequency and amplitude (a). The results obtained with
an excitation frequency ≈ 10 kHz. High frequency mode is prevalent for small separation
between the two shots (40 µs). The second picture is obtained for few seconds separation
of a pulse. A sandwich sample (aluminium skin, honeycomb core) has been tested for
skin-core debonding (b). Defects could be detected with a thermal loading of the sample.
The record of vibration of a truck cabin is given in (c). Electrical casing is small Al part
with rubber coating (d). Bonding quality is tested with artificial defects.
4.3. Laser shearographic system
Modern phase stepping optical systems used for aircraft industry have higher sensi-
bility and signal-noise ratio (SNR) in interferometric methods. Phase stepping optical
configuration (real-time phase, phase circulation and display) enable wrapped phase
mapping of surface deformation. Obtained data serve for signal processing and flaws
detecting. Proper filtering is introduced for better results.
Transferring compact measuring system Q 800 for full field represents contactless
NDT inspection for different materials (composite materials fiber glass reinforced plas-
tics, bonded composite materials). Delaminations, cracks, voids, impact damage, defects