ACOUSTIC-BACKSCATTERING STUDIES OF TRANSVERSE CRACKS IN COMPOSITE THICK LAMINATES

The distribution of first-ply transverse cracks in graphite/epoxy 0. 5-in. thick laminates was scanned by the acoustic-backscattering technique. The backscattering scans reveal a discrete number of characteristic dark bands in the case of specimens subjected to static loads or a low number of fatigue-load cycles. A dark band extending along the length of the specimen was obtained in specimens subjected to a high number of fatigue-load cycles. These dark bands reveal the three-dimensional distribution of transverse cracks situated in several adjacent planes. X-ray radiography shows the projection of the three-dimensional distribution of transverse cracks in the laminate plane and hence it may provide a low estimate of the distribution of transverse cracks in composite thick specimens.