Nondestructive Characterization of Impact Damage in Graphite/Epoxy Laminates

Abstract

Transient deformation and damage were studied in graphite/epoxy plates subjected to falling weight impact. The plates were 8-ply and 16-ply quasi-isotropic laminates clamped around a 12.7 cm (5 in.) diameter circumference. They were instrumented with surface and embedded strain gages and loaded by a 202 gr (0.445 lb) mass dropped from a height of 1.83 m (72 in.). The dynamic load history and imparted energy were obtained by means of an accelerometer attached to the impactor. Transient strains at various locations through the thickness and at various distances from the loading point were obtained. The characteristic features of the strain records are associated with specific failure modes in the laminate. The deformation history was also correlated with the induced damage as detected by X-radiography and ultrasonics. Impact damage is more extensive in the thicker laminate. Damage takes the form of delaminated strips parallel to the fiber direction in each ply and increasing in length from top to bottom. The length variation of consecutive delaminated strips is more pronounced in the thin laminate. Transient strain records corroborate the ultrasonic indications regarding the location of delaminations.