Slowness mapping of guided waves for disbond detection in honeycomb sandwich structures using laser ultrasonics

Disbonds between face sheets and core materials in honeycomb sandwich structures (HSSs) can severely compromise structural integrity, particularly in aerospace applications. This study presents a laser-ultrasonics-based guided wave visualization method for detecting and localizing disbonds in aluminum and composite HSSs without requiring baseline data or prior knowledge of defect characteristics. By exploiting wave propagation behavior in simplified HSSs, the method employs wavenumber-frequency filtering and slowness mapping to enhance damage visibility. Theoretical dispersion analysis and finite element (FE) simulations indicate that disbonds substantially reduce the guided wave velocity. Experimental validations on both aluminum and CFRP-aramid specimens demonstrate that the proposed method can accurately detect disbonds of various shapes and sizes. The approach provides intuitive, quantitative, and robust detection performance, confirming its potential as a reliable non-destructive evaluation method for complex sandwich structures.