Impact damage and damage tolerance of fibre reinforced advanced composite laminate structures

The primary objective of this work is to experimentally examine the effect of various geometric parameters on the impact damage and damage tolerance of thin carbon/epoxy plate and panel structures. Due to the number of parameters involved in a low velocity impact event and the complexity of the damage created, determining what effect individual parameters have is extremely demanding, especially when some of the parameters may even be coupled. However, by experimentally simulating in a controlled manner, either the impact event or the damage created, the effect of individual geometric parameters can be isolated and determined. A quasi-static indentation test has been used to simulate an impact event. The parameters of indenter size, nose shape, plate size and boundary condition, were examined. Four different plate failure modes were identified. Indenter nose shape was found to be the dominant geometric parameter, as a change in nose shape resulted in a change in failure mode and hence maximum load. From this work, a set of geometric parameters was selected for impact testing. Impact testing at various Incident Kinetic Energies (IKE) was performed on an instrumented drop weight impact rig. From examination of internal and external damage, the development of damage to increasing IKE was determined and shown to have four distinctive phases. Coupled with strike and rebound velocity measurementsa, non-linear relationship between IKE-damage area was established and a delamination threshold energy level of 1.1 J was calculated. Damaget olerance assessmenot f impacted panels was then performed in a Compression-After- Impact (CAI) rig. Strain gauge responses allowed global and local behaviour to be compared to intact specimens. It was found that once a critical damage size was surpassed, a gradual nonlinear degradation in compressive strength was observed until a point was reached where no further degradation in performance was attained. Furthermore, propagation of internal damage in a stable and unstable manner was directly linked to the nature of sublaminate buckling behaviour. Damaget olerance assessmenot f artificially delaminatedp anels loaded in compressionw as then performed. A single artificial delamination of various size, shape and orientation, embedded at the centre of a panel was examined. Delamination width was found to be the dominant geometric parameter. Hence, when comparing a circular delamination to an elliptical one of the same area, the effect of orientation and shape is aspect ratio dependent. Finally, a comparison of impacted and artificially delaminated panels was made.