DAMAGE MECHANISMS IN COMPOSITE LAMINATES IMPACTED BY A FLAT-ENDED IMPACTOR

In order to be able to predict impact damage, complex impact behaviour in laminate composites has to be well understood and quantitatively characterized. To achieve this, thick glass-fibre-reinforced laminates of various dimensions have been subjected to low-velocity impact with a flat-ended impactor in the energy range 15-3000 J. Post-impact examination of damage is carried out by visual inspection, diametric cross-sectioning, and ultrasonic C-scanning. A number of damage mechanisms have been observed, and their influence on impact behaviour is found to be generally dependent on the impact force or incident kinetic energy (IKE) level. Although post-impact techniques are very useful, impact force and IKE histories derived by using an instrumented drop-weight impact rig are essential to the quantitative interpretation of damage development. Delamination, fibre shear-out, and fibre fracture are found to be the predominant damage mechanisms in absorbing IKE and controlling the load-bearing capabilities of the laminates. They have been shown to occur in a sequential manner and to be geometry dependent.