Effects of imperfections on the mechanical behavior of a wire-woven bulk Kagome cellular metal under compression Sangil Hyun a , Ji-Eun Choi b , Ki-Ju Kang c, * a Simulation Center, Korea Inst. of Ceramic Eng. and Tech., Seoul 153-801, South Korea b Automobile Research Center, Chonnam National University, Kwangju 500-757, South Korea c School of Mechanical Systems Engineering, Chonnam National University, 300 Yongbongdong Bukku, Kwangju 500-757, South Korea article info Article history: Received 5 January 2009 Accepted 5 February 2009 Available online 19 March 2009 PACS: 62.20.x 68.55.Ln 81.17.d Keywords: Cellular metal Kagome truss Imperfections PBC (periodic boundary condition) Network analysis WBK (wire-woven bulk Kagome) abstract A new cellular metallic structure known as wire-woven bulk Kagome (WBK) has been recently intro- duced. The fabrication of WBK is done by assembling metal wires in six directions and being brazed at all crossing points. Namely, wires that are naturally easy to handle and have high strength with least defects are used as the raw material to fabricate a structure similar to the Kagome truss. Its mechanical strength and energy absorption capability has been shown to be superior to previously developed cellular metals. The effect of imperfections on the performance of WBK, however, has never been explored either numerically or experimentally. In order to investigate the mechanical characteristics of the WBK under compression, a new hierarchical simulation method was proposed in this paper. First, the behavior of the bulk WBK composed of infinite number of cells in perfectly uniform structure was simulated by finite element analysis conducted on a unit cell under periodic boundary conditions. Second, the equivalent moduli of single truss obtained from the finite element analysis were utilized in the network analysis to examine the effects of geometry and material property imperfections. The imperfections introduced in statistical manner were added on perfect WBK lattice structures, and numerical results of the compres- sive strength and its sensitivity on the defects were compared with experimental results. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction Cellular metals are well-known for their high mechanical strength and stiffness with low weight advantage [1]. Because they have high ratio of surface area to volume, they are used as medium for heat exchanger or fluid storage as well [1,2]. The first commer- cialized cellular metal is metal foam, whose engineering applica- tions are however limited due to its high manufacturing cost and relatively low mechanical strength caused by the random cell geometry. On the other hand, periodic cellular metals (PCM) with uniform cell geometry can enhance mechanical characteristics sig- nificantly. Among three types of PCM such as prismatic, shell, and truss, the truss-type of PCM with open cell structure is considered to possess multi-functional feature. Pyramidal [3,4], octet [5–7], and Kagome [8–10] trusses are typical truss-type PCMs proposed to date. The Kagome truss PCM is especially known to show high resistance against plastic buckling, high plastic deformation en- ergy, and low anisotropy. To utilize the superior mechanical performance of truss-type PCMs in various industrial applications, there have been a lot of manufacturing processes suggested for mass production. However, the suggested methods of PCMs still have lack of economic merit for the high fabrication cost. Kang and his colleagues [11,12] re- cently introduced a new fabrication approach by using metallic wires. The wire-woven bulk Kagome (WBK) based on the Kagome lattice structure [8,10] was fabricated by three-dimensionally weaving helical metallic wires in six directions. The assembled wires were fixed by brazing at all the crossing points. Even though the structure was composed of wavy wires, compression tests [12,13] and three point bending test [14] showed that the strengths are comparable to those of the ideal Kagome truss struc- ture with straight struts. The studies also reported that, even after reaching the peak point, it did not show unstable fracture phenom- enon, but rather, the descending rate of its strength was slow en- ough to absorb a large amount of mechanical energy. Thus, WBK is expected to be mass-produced at a low price by simply assem- bling continuous wires. Furthermore, its relatively low anisotropy may enable the bulk WBK to be machined like solid metal regard- less of orientation. A wide range of the diameter of wires from nano-meters to meters can be used in the fabrication of the WBK potentially to be constructed in many different length scales. Since WBK is assembled with continuous wires, it is also advantageous to fabricate and utilize in a form of multi-layered bulk materials. 0927-0256/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.commatsci.2009.02.007 * Corresponding author. Tel.: +82 62 530 1688; fax: +82 62 530 1689. E-mail address: kjkang@chonnam.ac.kr (K.-J. Kang). Computational Materials Science 46 (2009) 73–82 Contents lists available at ScienceDirect Computational Materials Science journal homepage: www.elsevier.com/locate/commatsci