Issue 17

V. Crupi et alii, Frattura ed Integrità Strutturale, 17 (2011) 32-41; DOI: 10.3221/IGF-ESIS.17.04 32 Computed Tomography analysis of damage in composites subjected to impact loading V. Crupi, G. Epasto, E. Guglielmino Department of Industrial Chemistry and Materials Engineering, University of Messina, Contrada di Dio, 98166 Messina – Italy vcrupi@ingegneria.unime.it; gepasto@ingegneria.unime.it ; eguglie@ingegneria.unime.it A BSTRACT . The composites, used in the transportation engineering, include different classes with a wide range of materials and properties within each type. The following different typologies of composites have been investigated: laminated composites, PVC foam sandwiches, aluminium foam and honeycomb sandwiches. Aim of this paper was the analysis of low-velocity impact response of such composites and the investigation of their collapse modes. Low velocity impact tests were carried out by a drop test machine in order to investigate and compare their structural response in terms of energy absorption capacity. The failure mode and the internal damage of the impacted composites have been, also, investigated using 3D Computed Tomography. K EYWORDS . Composites; Low velocity impact; Computed Tomography; Impact damage; Collapse modes; Transportation engineering. I NTRODUCTION he structures realized using sandwich technologies combine low weight with high energy absorbing capacity, so they are suitable for applications in the transport industry (automotive, aerospace, shipbuilding industry), where the "lightweight design" philosophy and the safety of vehicles are very important aspects. While sandwich structures with polymeric foams have been applied for many years, currently there is a considerable and growing interest in the use of sandwiches with aluminium foam core [1, 2] and with honeycomb core [3]. Composite structures are more susceptible to impact damage than a similar metallic structure, because impacts create internal damages, that often are undetectable by a simple visual inspection and this is a great problem in the real structures. This internal damage can cause drastic strength reduction and can grow under applied loads. For these reasons, the impact strength has been a factor in limiting the use of composite materials. Impact behaviour of sandwich structures is completely different from that of metals and composite monolithic laminates and is dominated by the deformation of the core [4], which gets crushed as transverse stresses become large. Impacts can induce damage to the skins, the core and the core-skins interface. Core deformation and failure are decisive factors for the energy absorption capacity of sandwich structures. With aluminium honeycomb cores, damage consists of crushing or “buckling” of cell walls in a region surrounding the impact point, while, in foam cores, damage looks more like a crack for low-energy impacts [4]. For these reasons, it is necessary to acquire a better understanding of their behaviour and collapse modes under impact loads. T