Porosity determination in thin graphite-epoxy composite laminates using histograms of ultrasonic C-scans

Evidence of a direct correlation between attenuation and porosity in graphite-epoxy composites can be found during a literature review of ultrasonic research. This paper presents the possibility of detecting and quantifying porosity in thin laminates using amplitude histogram data obtained from ultrasonic C-scans in the pulse-echo mode. Seventeen composite panels were manufactured under various curing pressures to generate different levels of porosity. Multiple C-scans of these panels and their associated amplitude histograms were generated. Trends were calculated for quantifying porosity with respect to mean histogram amplitude data. The data indicate an effect of the material properties on the trendline which mean that different materials will need to be calibrated for this technique. Repeatability of the method was verified. Finally the sensitivity of the method was checked by zooming in on sections of the C-scans that displayed elevated levels of porosity. Comparing mean values for the zoomed histograms to mean values for the bulk histograms showed an ability to detect small local changes in the porosity levels. This method shows good potential for quantifying porosity levels larger than 1%. More data are still needed for a wider range of porosities to build more confidence in the porosity estimation.