Exploiting Laser Doppler Vibrometry in Large Displacement Tests

Large-displacement vibration testing has assumed increasing importance to answer the need of predicting damages for excessive real life vibration. Moreover, the need for reducing weight is pushing towards the use of non-contact methods in such tests. Discrete Scanning Laser Doppler Vibrometry (SLDV) has resulted to be an important tool for contactless measuring the dynamic behavior of structures. However, the method suffers when high displacements are reached because the laser spot continuously moves on the target surface with an associated uncertainty on the actual measurement point location that increases proportionally to the increase of the deformation of the structure. Such a condition causes the vibration signal to look alike the one recorded by a Continuous Scanning Laser Doppler Vibrometry (CSLDV) approach, with sidebands that are more pronounced the higher the structure deformation is. This paper describes how SLDV can still be exploited for measuring on structures undergoing large displacements, with the further benefit of extracting information related to additional degrees of freedom deriving from the continuous scanning look-alike behavior of the measurement. This results in a better capability of the technique to extract incipient/potential damages on the structure under test. The concept is explored on simulated data representing a cantilever beam pushed to move at high displacements.