Numerical axial impact study of pultruded circular and square composite tubes S. Palanivelu 1 , W. Van Paepegem 1 , J. Degrieck 1 , D. Kakogiannis 2 , J. Van Ackeren 2 , D. Van Hemelrijck 2 , J. Wastiels 2 , K. De Wolf 3 and J. Vantomme 3 1 Department of Materials Science and Engineering, Ghent University, Sint-Pietersnieuwstraat 41, 9000 Gent, Belgium 2 Department of Mechanics of Materials and Constructions, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium 3 Royal Military Academy, Civil and Materials Engineering Department, Building G, Level 0, 8 Av. Hobbema, 1000 Brussels, Belgium Abstract. This paper focuses on the numerical energy absorption behaviour of pultruded circular and square cross sectional glass-polyester composite tubes under an axial impact loading case. In order to capture the typical failure modes such as delaminations, lamina bending, axial cracks and fibre fracturing, a new innovative approach was used using multiple shell elements, cohesive ele- ments and pre-defined seams. To predict the correct peak crush load and the corresponding energy absorption, the importance of the numerical modelling of multiple delaminations and triggering are discussed. Two types of triggering were chosen for the study. Finally, the results of this numerical investigation are compared with experimental data. The commercially available finite element code ABAQUS V6.7-3 Explicit was used for this study. 1. INTRODUCTION A great deal of research and development has been carried out in the past decades to design safer automobiles. Out of the factors considered for safety criteria, the crashworthiness has attracted significant attention due to its multiple functions. The functions of the crashworthiness structures are to (i) absorb the energy, (ii) keep the occupant compartments intact and (iii) ensure tolerable deceleration levels for driver and passengers during the crash event. To meet the above functions different forms of the energy absorbers and combinations of high strength metal alloys are used for crashworthiness structures [1]. On the other hand the energy absorption characteristics of the various composite structural elements have been experimentally and theoretically studied by several researchers [2–5]. Composites have a relative advantage in terms of the specific energy absorption, ease of manufacture and maintenance. Various variables control the energy absorption of the composite structures such as mechanical properties of the fibre and the matrix, fibre volume fraction, laminate stacking sequence, fibre architecture and the geometry of the tube. To decelerate the impactor, the failed tubes exhibit delaminations, lamina bending, axial cracks and fibre fracturing modes. Few static and dynamic numerical studies have been conducted to assess the energy absorption characteristics of composite tubes [6, 7]. In these studies the numerical modelling of the composite tubes was done with a single layer of shell elements. However, the numerical modelling of the multiple delaminations which causes the split of outer and inner plies of the composite tubes cannot be modelled with a single layer of shell elements. The consideration of the multiple delaminations approach is important to predict the correct energy absorption because it causes the separation of plies and loss in bending stiffness of each sub- laminate. Furthermore, the finite element modelling of triggering (which induces the stable and progressive crushing) plays a vital role to predict the peak crushing load of a composite tube. DYMAT 2009 (2009) 771–777 Ó EDP Sciences, 2009 DOI: 10.1051/dymat/2009108