Experimental Study on the Validity of a Q-factor Based Resonance Selection Criterion in Type-approval Vibration Tests for Shipboard Equipment

Type-approval vibration tests for shipboard equipment commonly apply sinusoidal sweep tests, using the Q-factor to select critical resonances for endurance evaluation. However, shipboard equipment generally exhibits multi-degree-of-freedom (MDOF) behavior under base excitation, and Q-factor validity as a vibration fatigue indicator remains unclear. In this study, we experimentally evaluated the applicability of Q-factor-based resonance selection using cantilever-type specimens and a shipboard electrical control panel. Specimens with identical material (S45C) and geometry, but varying thickness (3 mm ~ 5 mm) exhibited Q-factors of 29.5 ~ 60.7, while fatigue life correlated more strongly with bending stress than with Q-factor. In several cases, specimens with lower Q-factors failed earlier due to higher stress concentration. For the electrical control panel, we observed multiple closely spaced resonances (26 Hz ~ 50 Hz) with location- dependent Q-factors of 4.9 ~ 14.8. Random vibration tests (15 Hz ~ 70 Hz, 0.701 g RMS) caused fatigue failure at a transformer bracket within approximately 7 min, despite its Q-factor being similar to other components. The failure was governed by local stiffness degradation and mass-induced stress concentration rather than resonance sharpness. These results demonstrate that Q-factor alone is insufficient to assess vibration fatigue risk in MDOF shipboard equipment. Effective resonance selection should thus account for response location, structural stress characteristics, and time-dependent dynamic changes.