Abstract
During the impact of thin composite panels, well-defined flaps can develop on the exit face as a consequence of through-thickness penetration of the panel. For certain materials (for example, CFRP panels based on plies of plain-woven fabric) the flaps develop as four triangles, with the apex of each triangle at the point of impact. As the impactor is driven through the panel, the flap (i.e. crack) lengths increase, until complete penetration of the panel by the impactor occurs. In the experiments described within this paper, CFRP panels fabricated from epoxy resin reinforced with plain-woven carbon fibre fabrics have been impacted using controlled multiple impact tests. During these tests, the impactor is driven at a controlled velocity to a particular depth of penetration through the composite panel, withdrawn, and then driven further through the panel subsequently. The experimental results show that the dependence of the flap compliance is proportional to the square of the flap length, which is in agreement with theoretical predictions. This compliance/crack-length also enables a toughness value for the composite panel to be derived that is directly relevant to through-thickness impact. The relationship of this toughness value to measurements of the mode I toughness of the composite panel using single edge notch specimens is also discussed.