An experimental-finite element analysis on the kinetic energy absorption capacity of polyvinyl alcohol sponge Alireza Karimi, Mahdi Navidbakhsh ⁎, Reza Razaghi School of Mechanical Engineering, Iran University of Science and Technology, Tehran 16846, Iran Tissue Engineering and Biological Systems Research Lab, School of Mechanical Engineering, Iran University of Science and Technology, Tehran 16846, Iran abstract article info Article history: Received 30 January 2014 Received in revised form 22 February 2014 Accepted 2 March 2014 Available online 12 March 2014 Keywords: Polyvinyl alcohol sponge Helmet Finite element Kinetic energy absorption Energy loss Polyvinyl alcohol (PVA) sponge is in widespread use for biomedical and tissue engineering applications owing to its biocompatibility, availability, relative cheapness, and excellent mechanical properties. This study reports a novel concept of design in energy absorbing materials which consist in the use of PVA sponge as an alternative reinforcement material to enhance the energy loss of impact loads. An experimental study is carried out to mea- sure the mechanical properties of the PVA sponge under uniaxial loading. The kinetic energy absorption capacity of the PVA sponge is computed by a hexahedral finite element (FE) model of the steel ball and bullet through the LS-DYNA code under impact load at three different thicknesses (5, 10, 15 mm). The results show that a higher sponge thickness invokes a higher energy loss of the steel ball and bullet. The highest energy loss of the steel ball and bullet is observed for the thickest sponge with 160 and 35 J, respectively. The most common type of trau- matic brain injury in which the head subject to impact load causes the brain to move within the skull and conse- quently brain hemorrhaging. These results suggest the application of the PVA sponge as a great kinetic energy absorber material compared to commonly used expanded polystyrene foams (EPS) to absorb most of the impact energy and reduces the transmitted load. The results might have implications not only for understanding of the mechanical properties of PVA sponge but also for use as an alternative reinforcement material in helmet and packaging material design. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Polyvinyl alcohol (PVA) sponges are currently in widespread use for the removal and management of diffuse fluids/blood at surgical site [1]. They are also contemplated as the most attractive biomedical polymers owing to a combination of qualities, such as biocompatibility [2–5], highly hydrophilicity [6–8], excellent mechanical strength and flexibili- ty [4–7,9,10], thermal stability and absence of toxicity [11], availability, and relative cheapness [12]. However, the application of these versatile biomaterials has been limited to ophthalmic, plastic, and hand surgeries as a biocompatible biodegradable material. Recently, Karimi et al. [13] characterized the mechanical properties of a fabricated PVA sponge for tissue engineering applications. Their results showed the Young's modulus and maximum stress of 40 and 9.79 MPa for PVA sponge, respectively. Further tests were also carried out to measure the Young's modulus of the PVA sponge at higher strain rates. The results revealed the Young's modulus of 4.28, 208.33, and 187.51 MPa at the strain rates of 1, 20, and 100 mm/min, respectively [14]. The Young's modulus of the PVA sponges was also measured under longitudinal (38.91 MPa) and circumferential (33.34 MPa) loads. The maximum stress, in addition, in the longitudinal direction was 17.90% greater than that of the circumferential direction [15]. The mechanical behavior of PVA sponge has shown to be similar to rubber-like materials, such as time-dependent viscoelastic behavior which can be formulated by the visco-hyperelastic approach under low strain uniaxial loading [16–19]. Considering both the advantage of biocompatibility and suitable mechanical properties of the PVA sponges, they can be used as an alternative reinforcement material to enhance the mechanical properties of the materials for biomedical or industrial applications. The suitable mechanical properties of the PVA sponges es- pecially under fast strain rates would also enable them to be used as an energy absorber material for helmet design. However, a critical barrier to the use of the PVA sponge as an energy absorber material is a lack of knowledge on its kinetic energy absorption capacity. Among the en- ergy absorbing materials available in the market, expanded polystyrene foams (EPS) are often used for the design of the helmet liners [20,21], due to their capability of providing multidirectional resistance to im- pacts, combined with light weight and relatively low costs of production and excellent kinetic energy absorption capacity [22]. A way to improve the energy absorption properties of current helmets could be the use of non-conventional materials capable of higher energy absorption, while keeping the accelerations transmitted to the head at a safe level. Materials Science and Engineering C 39 (2014) 253–258 ⁎ Corresponding author at: School of Mechanical Engineering, Iran University of Science and Technology, Tehran 16846, Iran. Tel.: +98 21 77209027; fax: +98 21 73021585. E-mail address: mnavid@iust.ac.ir (M. Navidbakhsh). http://dx.doi.org/10.1016/j.msec.2014.03.009 0928-4931/© 2014 Elsevier B.V. All rights reserved. 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