Mode Prioritization for Low-Complexity Condition Monitoring of Metallic Components: A Sensitivity and Consistency Assessment of Damaged Aluminum Beams

Vibration-based condition monitoring of beam-like metallic components requires vibration modes that are both sensitive to damage and consistent across different damage locations and severities. This study evaluates the damage sensitivity of the first eight bending-mode frequencies measured from 19 aluminum-alloy 6063 cantilever beams instrumented with magnetoelastic vibration sensors. The examined configurations comprised one undamaged reference beam and 18 damaged beams combining six crack-like defect locations with three defect depths. Normalized absolute frequency shifts were used to determine the mean sensitivity of each mode, its response to increasing defect depth, and the consistency of this response across the examined locations. The combined modal response increased progressively with defect depth, although the magnitude of the change depended on the selected mode and defect location. Mode f₇ exhibited the highest mean sensitivity of 1.234%and amonotonic-consistency ratio of C₇=1, indicating an increasing response with defect depth at all six locations. Modes f₂ and f₄ also demonstrated complete monotonic consistency but lower overall sensitivity, whereas f₅ showed comparatively high sensitivity with greater dependence on defect location. Mode f₈ presented the lowest sensitivity and consistency. These findings indicate that the available modes do not need to be treated equally. Prioritizing modes that combine high sensitivity with consistent depth-dependent behavior could simplify the processing and interpretation of modal information for preliminary condition monitoring of metallic industrial components. Further repeated measurements and validation under operational conditions are required before diagnostic thresholds can be established.