An investigation of fracture mechanisms of carbon epoxy laminates subjected to impact and compression-after-impact loading

Abstract

Abstract A preliminary study has been carried out to characterise the damage mechanisms associated with impact and postimpact loadings in a number of laminates manufactured from different fibre architectures and manufacturing techniques. This work has revealed that woven, uniweave and Unidirectional tape laminates all have fairly similar impact characteristics, i.e. they sustained increasingly larger damage zones with impact energy, with the formation of a crater on the impacted surface and fibre fractures on the underside at higher impact energy levels. However, these laminates exhibited distinct impact damage morphologies; the woven had a quasi-circular morphology, the unidirectional tape was elongated in the longitudinal direction, and the uniweave was either of the two depending on the impact energy level. Post-impact compression failure of the unidirectional tape resulted from sub-laminate buckling and of the uniweave laminates by transverse shear. The woven laminates, on the other hand, failed by a combination of the two mechanisms, and whilst stitching was successful in restricting sub-laminate buckling, no appreciable improvement in CAI strength was recorded. This suggests that the dominant failure mechanism operating in the woven laminates is transverse shear.