Analysis of sound and vibration interaction on a crack and its use in high-frequency parameter selection for vibro-acoustic modulation testing

Influence of Sensor Position and Low-Frequency Modal Shape on the Sensitivity of Vibro-Acoustic Modulation for Impact Damage Detection in Composite Materials

“…Alternative and more robust strategies are required to avoid the need of detailed and time-consuming experimental or numerical modal analyses and to improve the reliability of the technique. Monitoring procedures involving the use of multiple-mode or broadband excitations [25][26][27]31,34,38] have been explored in recent years, even though they These results provide clear experimental evidence of the strict link between the sensitivity to damage of the VAM technique and the location of the sensor with respect to the deformation shape activated by the pump vibration. They also indicate that an accurate modal analysis of the system to be monitored is a necessary preliminary step for identifying the best excitation frequencies and the associated optimal sensor placement that would allow to fully exploit the potential of conventional fixed-frequency VAM approaches.…”

“…Alternative and more robust strategies are required to avoid the need of detailed and time-consuming experimental or numerical modal analyses and to improve the reliability of the technique. Monitoring procedures involving the use of multiple-mode or broadband excitations [25][26][27]31,34,38] have been explored in recent years, even though they have been mainly tested with specific reference to the high frequency probe excitation. The outcomes of this study suggest, however, that the use of a frequency-swept pump excitation may be an effective way to increase the reliability of the indications provided by VAM measurements.…”

“…The dependence of the VAM performance on the frequencies of the pump and probe excitation has been reported in the literature not only for impact damage in composite laminates, but also for other classes of materials, such as metals and concrete, and for a variety of sources of nonlinearity, including fatigue cracks in metal components [13,[25][26][27]; bolt looseness in mechanical joints [28]; artificial scatterers or kissing bonds [29,30]; and diffuse micro-and macro-cracking [17].…”

“…To overcome this need, the authors proposed to use a swept probe excitation, so as to inspect a wide range of probe frequencies in a single test. A sweep signal was also used for probe excitation in [26,27] to examine the influence of the probe frequency on the capability of the technique to detect fatigue cracks in aluminum beams. The experimental results indicated that the modulation reached a peak when one of the sideband frequencies coincided with a resonance of the system, thereby suggesting that the best crack sensitivity is achieved when selecting a probe frequency that is shifted from the resonance frequency by a distance equal to the applied pump frequency.…”

“…This effect was attributed to the different amounts of relative motions occurring at the crack interfaces for the different pump frequencies. In this respect, it may be worth noting that most studies highlight the importance of exciting the damaged area with sufficient strain energy to activate its nonlinear behavior [13,26,27,[29][30][31]33]. This necessity has suggested the adoption of VAM approaches based on the application of multiple pump excitation modes to reduce the chance of having a node of the deformation shape positioned at the damage location [15,25,30,31,34].…”