Reliability of ultrasonic detection of embedded defects in glass fibre reinforced composite

The reliable detection of defects with ultrasonic C–scan method in glass fibre reinforced composite plate represents a challenging task due to the high reflectivity of glass fibres. Pulse–echo ultrasonic C–scan method was used for examination of various processing defects in a composite plate produced by vacuum infusion process. Defects were embedded between the layers of the test plate varying in shape, volume, and depth. During the specimen preparation with VI, air was introduced through small non–sealed spot in vacuum membrane. On the selected location, the PVC, aluminium foils, and aluminium chips were inserted between layers. Different frequencies and gate settings were used to find the best possible set of parameters to detect defects. The scanning results show good visibility of PVC foils, chips, and porosity at the surface. On the contrary, with this methods, very thin aluminium foils were not detected.