ACOUSTIC MICROSCOPY IN COMPOSITE MATERIALS TESTING

In this paper an application of acoustic microscopy to non-destructive characterization of composite materials used in aerospace structures is described.The inspected materials are multilayer graphite epoxy laminates. The specimens are built up with alternated layers of different orientations.The examined samples are damaged through impacts of different energy levels. These impacts produce defects such as delaminations and fiber fractures.The acoustic microscopy equipment, developed by CISE, is a computer aided system allowing automatic inspections. An area of about lm × l.5m may be scanned by an ultrasonic probe with a pitch of 0.01mm. The echo signals are digitized and sent to a personal computer which processes data and supplies B, C and D-scan images. The examination of slices of different depths is also possible.In these experiments the immersion pulse echo technique by means of a 25 MHz probe is applied and an area of 24.96mm × 24.96mm is inspected.The main results are here described. They show that the different layers of the composite material may be identified and the location and extension of damage are evidenced. The type of damage (delamination with a conical distribution in the volume) is observed.The application of acoustic microscopy to nondestructive characterization of these composite materials seems promising. However more systematic measurements are necessary in order to obtain more quantitative data.