Adhesive mass as the dominant source of natural frequency variability in production-batch aluminium honeycomb sandwich panels

Natural frequency variability across nominally identical aluminium honeycomb sandwich panels from a single production batch is dominated by differences in adhesive quantity, not by face sheet or core geometry, a finding with direct implications for manufacturing quality control and structural dynamic prediction. This finding applies to the commercial aluminium/polyurethane honeycomb sandwich system investigated and is not expected to generalise to film-adhesive aerospace systems. This study quantifies this relationship experimentally across 35 commercial panels from the same production batch using three field-compatible measurement methods. First, a portable single-microphone acoustic test, requiring no contact sensors or multi-channel analyser, identifies panel natural frequencies with correlation r = 0.984 against laboratory experimental modal analysis (mean percentage error 1.1%, RMSE < 0.5 Hz), validating its suitability as a field-deployable alternative. Second, a weight-balance method derives total adhesive mass per panel from scale measurement and image-measured geometry, yielding a signal-to-noise ratio of 8.9 for between-panel ranking. Third, automated edge cross-section image processing quantifies face sheet thickness (coefficient of variation 2.7%) and core height with sub-pixel precision. Combined, a precision scale and an edge-imaging camera predict 84% of first-mode frequency variance across the batch R ² _LOO = 0.839 without any vibration measurement, demonstrating a practical baseline for factory-floor quality screening. Adhesive quantity, not face sheet thickness, is identified as the dominant source of natural frequency variability, with total panel weight ( r = −0.855, p < 0.001) being the single most reliable frequency predictor.