Non-destructive triaxial vibroacoustic modal testing with a single sound transducer: a railway sleeper case study

Vibrational experimental modal analysis (EMA) is among the most widely used modal parameter estimation techniques. However, it has several drawbacks, such as requiring accelerometer(s) mounting and using local measurements. Therefore, this study investigated whether vibroacoustic modal testing (VMT), a rarely studied method, would be a suitable alternative for EMA. In this context, a comparative case study was conducted on railway sleepers. First, modal parameter determination techniques in the literature were compared (time/frequency-domain, with/without normalisation, structural/acoustic excitation, and acoustic/vibrational response). Then, VMT and EMA test setups were reorganised considering the deficiencies identified in the literature. As a result, the difference between the VMT and EMA resonance frequency and damping ratios in the proposed mode shapes is determined as 0.06% and 3.46%, respectively. Consequently, this novel VMT setup using a single microphone that can take non-destructive, non-contact, and non-local (triaxial) measurements has been proven to provide reliable results and is recommended for future studies.