Across the Picket Fence: Influence of Sampling Frequency in Automatic Impact Modal Testing

Title:
Across the Picket Fence: Influence of Sampling Frequency in Automatic Impact Modal Testing
Abstract:
Automatic impact modal testing is a technique gaining momentum in recent years thanks to the popularization of Scanning Laser Doppler Vibrometry. These systems allow automatizing the output measurement of thousands of degrees of freedom in a short time. The use of automatic impact modal hammers allows automatizing the excitation input and broadband excitation without loading a structure with an extra mass or other drawbacks. However, the impact force repeatability is a prominent concern among test engineers, especially those who work with materials with non-proportional force/response ratios. Assessing the impact force repeatability of a given automatic modal hammer or test rig is necessary in order to ensure the right response level is measured impact after impact. The assessment procedure can be misleading if not done right. Studying the automatic modal hammer repeatability under typical modal test conditions invariably leads to impact signals strongly distorted by the so called picket fence effect. This results in impacts sampled by only 3–4 data points; insufficient to accurately describe the actual impact force signals and the short contact times between hammer tip and structure. In the reality, the impacts are of larger magnitudes and shorter contact times than what is shown by the analyzer in typical test conditions. This work studies the influence of the sampling frequency and the test structures used on the repeatability assessment of automatic impact modal hammers. Impact force signals are acquired in this work with enough resolution to eliminate the picket fence effect and truly evaluate how repeatable and reproducible automatic impacts are. The practicality of the procedure, which involves very large datasets and long testing times, is discussed. Guidelines are offered at the end of the paper for a successful repeatability and reproducibility assessment of automatic impact modal hammers.
Year:
2019
Publication type:
Conference contribution
Conference:
Proceedings of the 36th IMAC, A Conference and Exposition on Structural Dynamics 2018
Book title:
Special Topics in Structural Dynamics, Volume 5
Publisher:
Cham: Springer International Publishing
ISBN:
978-3-319-75390-4
Pages:
137-149
Language:
English
Document status:
Published
PubListerURL:
https://publister.bib.th-wildau.de/publister/public/publication/2563
Keywords:
Experimental modal analysis; Sampling; Automatic modal hammer; Impact modal testing; Validation
Alarcón, D., Schneider, S., Kamenzky, R., & Blaschke, P. (2019). Across the Picket Fence: Influence of Sampling Frequency in Automatic Impact Modal Testing In Nikolaos Dervilis, Special Topics in Structural Dynamics, Volume 5 (pp. 137-149). Cham: Springer International Publishing.
@inproceedings{2563,
    author           = {Alarcón, Daniel and Schneider, Sarah and Kamenzky, Robert and Blaschke, Peter},
    title            = {Across the Picket Fence: Influence of Sampling Frequency in Automatic Impact Modal Testing},
    editor           = {Nikolaos Dervilis},
    year             = {2019},
    pages            = {137-149},
    publisher        = {Springer International Publishing},
    address          = {Cham},
    isbn             = {978-3-319-75390-4},
    booktitle        = {Special Topics in Structural Dynamics, Volume 5},
    doi              = {10.1007/978-3-319-75390-4_11},
    url              = {https://link.springer.com/book/10.1007/978-3-319-75390-4#about},
}


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