Comparative research on the crashworthiness characteristics of woven natural silk/epoxy composite tubes R.A. Eshkoor a,⇑ , S.A. Oshkovr b , A.B. Sulong a , R. Zulkifli a , A.K. Ariffin a , C.H. Azhari a a Department of Mechanical and Materials Engineering, Faculty of Engineering, Universiti Kebangsaan Malaysia 43600 Bangi, UKM, Malaysia b Department of Mechanical and Manufacturing Engineering, Aalborg University, DK-9220 Aalborg, Denmark article info Article history: Received 29 July 2012 Accepted 18 November 2012 Available online 8 December 2012 Keywords: Trigger mechanism Natural silk composite Energy absorption Progressive failure abstract This study investigated the energy absorption response of triggered and non-triggered woven natural silk/epoxy composite rectangular tubes subjected to an axial quasi-static crushing test. The rectangular composite tubes were prepared by the hand lay-up technique using 12 layers of silk fabric with a thick- ness of 1.7 mm and tube lengths of 50, 80, and 120 mm. The parameters measured were peak load, energy absorption, and specific energy absorption (SEA). In both triggered and non-triggered tubes, the SEA values decreased with increasing length of the composite specimen. On the contrary, total energy absorption increased with increasing length of the composite specimen. The peak load in triggered spec- imens is nearly half of that in non-triggered specimens. Deformation morphology shows that the speci- mens failed in two distinct modes: local buckling and mid-length buckling. The non-triggered composite tubes exhibited catastrophic failure, whereas the triggered composite tubes only exhibited progressive failure. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction High specific strength and specific stiffness are desirable mechanical characteristics for structural materials [1,2] that are particularly used in the transportation field, where weight is an important criterion in addition to crashworthiness. Lower weight corresponds to less fuel consumption and fewer environmental hazards [3,4]. However, crashworthiness still remains the most important criterion in designing structures. Crashworthiness is de- fined as the capability of a structure to protect its occupants during a survivable collision [5]. Fiber-reinforced composites are now used in the transportation industry to achieve better crashworthi- ness and build lighter vehicles [6–14]. To date, customer demand for environmentally friendly materials has been increasing and government legislations have been becoming stricter. Hence, man- ufacturers are prompted to make use of natural fibers as reinforce- ments because of their abundance, renewability, low density, low cost, and high tensile strength. Different natural fibers mostly plant based fibers were objects of previous researches [15]. Natural silk as an animal based fiber has been gaining increasing attention compared with other natural fibers because of its novel mechanical properties, such as high strength, elasticity, environmental friendliness [16], and high moisture resistance [17]. However, despite these excellent proper- ties, natural silk is rarely used in investigating the crashworthiness of composite structures [18–20]. Thus, the behaviors of sample structures with new materials under different conditions should be completely analyzed in laboratories prior to application. Regardless of the component of composite structures, stable and progressive failure is key in determining the maximum energy absorption level [21]. Generally, composite structures fail in a cat- astrophic manner unless a certain mechanism such as triggering is employed [22–24]. Different trigger configurations, such as cham- fer, tulip, and plug initiator, have been previously studied [13,23,25–28]. Each configuration influences the crashworthiness characteristics of composite structures differently. Composite structure failure varies depending on geometric and material prop- erty [29]. This dependence of composite structure failure on sev- eral variations makes this type of failure very complicated. In brittle composite structures, failure occurs because of the forma- tion and growth of microcracks. This phenomena allow various functions, such as wedge debris formation, interlaminar or intra- laminar cracks, and buckling, to contribute to structural failure [29]. Studies concerning external triggers as well as the utilization of woven natural silk as fiber reinforcement in composite struc- tures have been very limited. Thus, the behavior of woven natu- ral silk/epoxy composite tubes with and without triggering 0261-3069/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.matdes.2012.11.030 ⇑ Corresponding author. Tel.: +60 3 89216504. E-mail addresses: sorena.a@eng.ukm.my, sorena.a2569@gmail.com (R.A. Eshkoor). Materials and Design 47 (2013) 248–257 Contents lists available at SciVerse ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes