Issue 17

V. Crupi et alii, Frattura ed Integrità Strutturale, 17 (2011) 32-41; DOI: 10.3221/IGF-ESIS.17.04 40 Figure 17 : Tomographic images of the damaged honeycomb core panels after the impact ( d = 3 and 6 mm, v = 4 m/s). The values of energy required to produce the complete failure of the investigated composites are reported in Fig. 18. Figure 18 : Energy required to produce complete failure of the investigated composites. C ONCLUSIONS omposite materials, especially in the form of sandwich structures, with their combinations of low weight and high energy absorbing capacity are very attractive for applications that require lightweight structures, such as the transport industry, where problems of collision and crash have increased in the last years. This study experimentally investigates the impact behaviour of different typologies of composites, comparing their impact response in terms of energy absorption and failure mode. Low velocity impact tests were carried out on the following typologies of composites: laminated composites, PVC foam sandwiches, aluminium foam and honeycomb sandwiches. The test results confirm that the Kevlar fibre reinforced layers had, as expected, good impact performance and that the PVC foam sandwiches, which have an higher thickness, required an higher energy amount to produce the complete failure with respect to the laminates and aluminium sandwiches, but different failure modes were observed during the tests. An advanced non-destructive technique like X-ray tomography was used to investigate the failure mode and the damage of the composites subjected to impact loading by means of the analysis of cross-sectional views. The aluminium sandwiches experienced ductile fracture with large out-of-plane displacement compared to the failure mode of the laminates and PVC foam sandwiches and this makes the damage detection procedure easier. Moreover, their structures are relatively intact compared to the more catastrophic and localized fracture of the polymeric composites and, in consequence, they exhibit a better post-impact strength. AFS Schunk t = 11 mm AFS Alulight t = 11 mm Honeycomb d = 6 mm t = 11 mm Honeycomb d = 3 mm t = 11 mm PVC foam sandwich t = 25 mm GFRP laminate t = 9 mm Glass + kevlar fiber laminate t = 10 mm 0 25 50 75 100 125 150 175 200 225 250 275 300 Disspated energy/ J C