Phase congruency for damage mapping in composites

Abstract

In non-destructive evaluation of composites, an efficient method for mapping damage is critical for assessing the severity of damage in a specimen. Phase congruency (PC) is a technique for detecting edges in images. This paper adapts this technique to map damage in composite plates. The method utilizes two-dimensional wavefield measurements of a guided wave propagating through the specimen. Each time step of the two-dimensional wavefield is analyzed with the modified PC measure. The results of each time step are aggregated yielding a full field map of the specimen identifying the damage. The approach was validated on numerical and experimental data sets for simulated damage in a plate. In concept, the PC measure exploits the fact that the phase of the spatial Fourier components of a signal have an equal value at a discontinuity. To do this, the measure compares the magnitude of the sum of the components to the sum of the magnitude of the components. The upper bound of this ratio is unity. PC values approaching unity indicate the phases of each the components are aligned and identify a discontinuity. This measure was adapted for the present case; a strong interrogating wave dominates the wavenumber spectrum obscuring low amplitude wavenumber information related to discontinuities. The resulting technique provides a map of damage in a two-dimensional space without necessitating the use of a model or baseline measurement.