The effect of processing conditions on the energy absorption capability of composite tubes Jose ´ Daniel D. Melo * , Andre ´ Luiz S. Silva, John Edward N. Villena Department of Materials Engineering, Universidade Federal do Rio Grande do Norte, Campus Universita ´ rio, S/N, Natal – RN, 59072-970, Brazil Available online 4 March 2007 Abstract Structures capable of absorbing large amounts of energy are of great interest, particularly in the automotive and aviation industries, in an effort to reduce the impact on passengers in the case of a collision. The energy absorption properties of composite materials can be tailored, thus making them an appealing option as a substitute of more traditional materials in applications where energy absorption is crucial. In this research, the effect of the processing conditions (with or without vacuum) on the specific energy absorption capacity of composite tubes was investigated. Tubes of circular and square cross sections were fabricated using orthophthalic polyester resin and plain weave E-glass fabric with fibers oriented at 0°/90°, with respect to the tube axis. Test specimens consisting of tube segments were prepared and tested under quasi-static compression load. Test results indicate that, among the conditions considered, tubes of circular cross section fabricated under applied vacuum display the highest level of specific energy absorbed. Ultimately, this investigation dem- onstrates the potential for tailoring the energy absorption properties of composite materials through controlled processing conditions. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Crashworthiness; Energy absorption; Composite materials; Crush testing 1. Introduction Crashworthiness may be defined as the capability of a vehicle to protect its occupants from serious injury or death in case of accidents of a given proportion [1–3]. Therefore, it is an essential parameter for vehicle and aircraft design and, due to its importance, it has been a topic of great interest for engineers and scientists over the years. Crash- worthy efficient structures must be able to dissipate large amounts of energy in the event of a crash. Efforts have been directed towards designing vehicle structures capable of absorbing the maximum amount of energy, while the pas- senger compartment retains its functional integrity. With composite materials, structures can be designed using a variety of reinforcement types and orientations, various matrix materials, and lay-up sequences, to achieve superior properties. Properties of composite materials can be tailored to provide specific energy absorption capabili- ties superior to those of metals. Therefore, composites are appealing options to substitute more traditional mate- rials in crashworthiness applications. Moreover, high spe- cific mechanical properties such as stiffness and strength, design flexibility and reduced weight are indeed advanta- geous, especially to the automotive and aircraft industries. Previous investigations have indicated that the energy absorption mechanisms in composite materials are more complex than those observed in conventional materials, and include matrix cracking, delamination, and fiber breakage [1,3]. In addition to the material properties, in the event of a collision, the dissipated energy depends also on geometry factors [1,3]. Trigger mechanisms can be used to control collapse, thus increasing the dissipated energy. In this case, the trigger is a stress concentrator, which is located at a specific location within the structure, to cause failure in a progressive crushing mode. Specific energy absorption has been defined as the energy absorbed per unit mass of material, i.e., Es ¼  r=q, 0263-8223/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.compstruct.2007.03.001 * Corresponding author. Fax: +55 84 3215 3703. E-mail address: daniel.melo@ufrnet.br (J.D.D. Melo). www.elsevier.com/locate/compstruct Composite Structures 82 (2008) 622–628