Effects of Interleaving on the Impact and Impact Fatigue Responses of Cross-ply Carbon Fibre/Epoxy Laminates

Abstract

The impact performance of carbon fibre/epoxy (CF/EP) laminates with and without interleaving was investigated by an instrumented falling weight impact (IFWI) method both in the perforation and the subperforation ranges. Tests in the subperforation range were performed either by single impacts with various energy levels or by multiple impacts (impact fatigue) at the same incident energy (E_in). In the former case both the maximum load (F_max) and the maximum deflection (x_max) increased with increasing E_in. Under impact fatigue conditions the absorbed energy (E_a) and x_max increased, whereas F_max decreased with increasing numbers of impacts (NOI). It was recommended to relate the stiffness deterioration of the plates to the change in the initial or secant slope of the rebound fractograms represented as F-x traces. The effects of position, number and thickness of the adhesive interlayers (A) incorporated were also studied. Positioning the interleaf in the neutral axis (mid-plane) of the composite plates does not enhance the resistance to delamination are low energy levels. In contrast, interleaving in the compression and/or tension sides of the plates depressed delamination, detected by ultrasonic C-scanning, considerably. The cone of damage across the thickness became narrower due to interleaving, as revealed by microscopic and ultrasonic B-scanning techniques.

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