Case Studies of LDV-Aided Dynamic Testing

2012 ◽  
Vol 226-228 ◽  
pp. 2066-2071 ◽  
Author(s):  
Kao Shan Dai ◽  
Xiao Song Ren ◽  
Qing Jun Chen ◽  
Bin Zhao
Keyword(s):  
Prestressed Concrete ◽  
Dynamic Testing ◽  
Laser Doppler Vibrometer ◽  
Laser Doppler ◽  
Vibration Measurement ◽  
Structural Vibration ◽  
Structural Dynamic ◽  
Vibration Sensors ◽  
Sensing Technology ◽  
Contact Sensing

The laser Doppler vibrometer is a non-contact sensing technique developed based on the Doppler effect of a laser beam emerging from a subject surface. As a vibration transducer, the laser Doppler vibrometer offers many advantages over the conventional contact vibration sensors. It allows remote, non-intrusive measurement of structural vibration and it is very useful in scenarios when traditional contacting measurement is inconvenient. In this paper, four laser-based structural dynamic studies were presented and some results were briefly reported, which include laboratory dynamic testing of a bolted steel beam, a scaled-down high-rise building model, and a prestressed concrete reaction wall, and field vibration measurement of a viaduct bridge. Through these demonstrating cases, it is anticipated to help civil engineers get familiar with the laser-based sensing technology and to extend their selections for effective measurement approaches during experimental research.

Temperature coefficient of Young’s modulus of silver microwhiskers determined by a laser Doppler vibration measurement

2021 ◽  
pp. 2150350
Author(s):  
Yijun Jiang ◽  
Mingyuan Lu ◽  
Shiliang Wang ◽  
Han Huang
Keyword(s):  
Temperature Dependence ◽  
Temperature Coefficient ◽  
Single Crystals ◽  
Young’S Modulus ◽  
Vapor Deposition ◽  
Physical Vapor Deposition ◽  
Young's Modulus ◽  
Laser Doppler Vibrometer ◽  
Laser Doppler ◽  
Vibration Measurement

Temperature dependence of Young’s modulus of Ag microwhiskers was determined by a laser Doppler vibrometer. The Ag whiskers with diameters in sub-microns were synthesized by the use of physical vapor deposition (PVD). They have a five-fold twinned structure grown along the [1 1 0] direction. The temperature coefficient of Young’s modulus was measured to be [Formula: see text] ppm/K in the range of 300 K to 650 K. The measured values are very close to the reported values of [Formula: see text] ppm/K for bulk Ag single crystals. This finding can benefit the design of Ag-based micro/nano-electromechanical systems or micro/nano-interconnectors operated at elevated or lowered temperatures.

scholarly journals Damage Identification by Using a Self-Synchronizing Multipoint Laser Doppler Vibrometer

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Chong Yang ◽  
Yu Fu ◽  
Jianmin Yuan ◽  
Min Guo ◽  
Keyu Yan ◽  
...  
Keyword(s):  
Mode Shape ◽  
Natural Frequencies ◽  
Damage Identification ◽  
Reference Beam ◽  
Laser Doppler Vibrometer ◽  
Laser Doppler ◽  
Vibration Measurement ◽  
Mode Shapes ◽  
Interference Signal ◽  
Short Period

The vibration-based damage identification method extracts the damage location and severity information from the change of modal properties, such as natural frequency and mode shape. Its performance and accuracy depends on the measurement precision. Laser Doppler vibrometer (LDV) provides a noncontact vibration measurement of high quality, but usually it can only do sampling on a single point. Scanning LDV is normally used to obtain the mode shape with a longer scanning time. In this paper, a damage detection technique is proposed using a self-synchronizing multipoint LDV. Multiple laser beams with various frequency shifts are projected on different points of the object, reflected and interfered with a common reference beam. The interference signal containing synchronized temporal vibration information of multiple spatial points is captured by a single photodetector and can be retrieved in a very short period. Experiments are conducted to measure the natural frequencies and mode shapes of pre- and postcrack cantilever beams. Mode shape curvature is calculated by numerical interpolation and windowed Fourier analysis. The results show that the artificial crack can be identified precisely from the change of natural frequencies and the difference of mode shape curvature squares.

Laser Doppler Vibrometry for Structural Dynamic Characterization of Rotating Machinery

2013 ◽  
Vol 415 ◽  
pp. 538-543
Author(s):  
Paolo Castellini ◽  
Milena Martarelli ◽  
Enrico Primo Tomasini
Keyword(s):  
Laser Beam ◽  
Vibrational Analysis ◽  
Laser Doppler ◽  
Structural Vibration ◽  
Vibration Velocity ◽  
Testing Time ◽  
Laser Doppler Vibrometry ◽  
Structural Dynamic ◽  
Full Field ◽  
Continuous Scanning

Laser Doppler Vibrometry (LDV) is a well established technique able to accurately measure vibration velocity of any kind of structure in remote, i.e. non-intrusive way, this allowing to overcome the problem of mass loading, typical of contact sensors as accelerometers and strain-gauges, which has strong influence in case of lightweight structures. Moreover, the possibility of driving automatically the laser beam, by means of moving mirrors controlled with galvanometer servo-actuators, permits to perform scanning measurements at different locations with high spatial resolution and reduced testing time and easily measure the operational deflection shapes (ODS) of the scanned surface. The exploitation of the moving mirrors has allowed to drive the laser beam in a continuous way making it to scan continuously over the structure surface and cover it completely. This way of operation, named Continuous Scanning LDV, permits to perform full-field measurements, the LDV output carrying simultaneously the time-and spatial-dependent information related to the structural vibration. A complementary strategy making use of the LDV coupled with moving mirrors is the so called Tracking LDV, where the laser beam is driven to follow a moving object whose trajectory must be known a priori or measured during operation (e.g. via an encoder in the case of rotating structures). In this paper some applications of the Tracking Laser Doppler Vibrometry (TLDV) and Continuous Scanning Laser Doppler Vibrometry (CSLDV) will be described they concerning, specifically modal and vibrational analysis of rotating structures.

scholarly journals Development and Validation of Bone Models using Structural Dynamic Measurement Methods

2019 ◽  
Vol 5 (1) ◽  
pp. 343-345
Author(s):  
Constanze Neupetsch ◽  
Eric Hensel ◽  
Michael Werner ◽  
Sven Meißner ◽  
Jan Troge ◽  
...  
Keyword(s):  
Modal Analysis ◽  
Laser Doppler Vibrometer ◽  
Cortical Layer ◽  
Vibration Measurement ◽  
Parameter Determination ◽  
Practical Implementation ◽  
Structural Dynamic ◽  
Modal Damping ◽  
Artificial Bones

AbstractVibration measurement and signal analysis methods are common to evaluate the functionality and characteristics of technical components in different industrial and scientific areas. Modal analysis for example is a standard method to characterize the dynamic behavior of a structure and enables the development of validated bone models. The state of the art of analyzing bone structures does not include the modal damping, although it has a significant influence on the dynamic characteristics. Within the presented investigations, the modal analyses have been performed contactless with respect to excitation and response acquisition, which implies that there are no influences of shakers or sensor couplings. Therefore, an automatic impulse hammer and a 3D Scanning Laser Doppler Vibrometer were used for excitation and response detection. Various supports of the test specimens, surface pretreatments, excitation points and excitation impulses were examined to optimize the measurement setup and process. Experimental modal analysis data were analyzed by curve fitting methods to determine the modal parameters. To evaluate different structures and effects of damping, 3D printed artificial bones and animal in vitro bones were used to perform the measurements. To produce the cortical layer of the artificial bone models, volume models were generated based on medical image data and printed by polyamide-based selective laser sintering. The cancellous bone was represented by different foam fillings for the artificial bones. Thereby, the variation of the porosity was achieved by using different mixing ratios of polyurethane foam and hardener. Furthermore, the modal damping parameters were determined from the measurement of animal bones. The measurement time was optimized during the practical implementation of the parameter determination to minimize the influence of drying and decomposition processes on the measurement results.

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