Digital Element Approach for Simulating Impact and Penetration of Textiles
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International Journal of Impact Engineering 37 (2010) 552–560 Contents lists available at ScienceDirect International Journal of Impact Engineering journal homepage: www.elsevier.com/locate/ijimpeng Digital element approach for simulating impact and penetration of textiles Youqi Wang a,*, Yuyang Miao a, Daniel Swenson a, Bryan A. Cheeseman b, Chian-Feng Yen b, Bruce LaMattina c a Department of Mechanical and Nuclear Engineering, Kansas State University, Manhattan, Kansas 66506, USA b US Army Research Laboratory, Aberdeen Proving Ground, MD 21005, USA c US Army Research Office, Durham, NC 27703, USA article info abstract Article history: A micro-scale computational tool, based upon an explicit digital element method (DEM), has been Received 2 March 2009 developed for numerical simulation of ballistic impact and penetration of textile fabrics. In this approach, Received in revised form each yarn is digitized as an assembly of digital fibers. Each digital fiber is further digitized into a short 25 September 2009 digital rod element chain connected by frictionless pins (nodes). A search is conducted to find contacts Accepted 23 October 2009 between adjacent digital fibers. If a contact is detected, compressive and frictional forces between fibers Available online 1 November 2009 will be determined, based upon contact stiffness and friction coefficient. Nodal forces are calculated for each time step. Nodal displacements are determined using an explicit procedure. Because the digital Keywords: High speed penetration element approach operates on a sub-yarn micro-scale, one can determine textile penetration resistance Digital element simulation based upon sub-yarn scale properties, such as inter-fiber compression, friction, and fiber strength. Ballistic resistance Research presented in this paper includes three parts. First, the explicit digital element algorithm used in Fabrics dynamic simulation is explained. Second, the approach is used to generate 2-D woven fabric micro- Body armor geometries and to simulate ballistic penetration processes. Third, numerical results are compared to high resolution experimental impact and ballistic test data. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction a ballistic textile is manufactured and its resulting configuration directly influences its behaviours. Compliant textile garments developed for protection have been Since the 1960s, numerous numerical methods for simulating produced for thousands of years – from layers of linen utilized by textile penetration have been developed. However, the design and the ancient Greeks through layers of silk worn by medieval Japa- development of textile armor systems have been driven primarily nese samurai. In the late 19th century the U.S. military also used silk by experiments and experience. Numerical models typically have body armor. During World War II, the ‘‘flak jacket’’, constructed of not been used to predict design of armor systems. Rather, they have ballistic nylon, was developed. However, none of these early been used to provide insight into the relative importance of specific protective textiles could resist a high velocity bullet. In the late material parameters that influence performance. Although textile 1960s, Du Pont invented Kevlar, an aramid material, the first bullet- performance is directly related to the manufacturing process and resistant fiber. This ushered in a new era of textile armor that its resulting fabric architecture, most of the important details continues to progress toward more efficient systems, offering related to fabric micro-structure and filament-level physics, such as exceptional protection against bullet penetration. While Kevlar was yarn denier, end count, tow structures, filament spatial paths, and the first ballistic material from which modern body armor could be fiber-to-fiber interaction were not accurately modeled in previous constructed, there are presently several other fiber types used in numerical techniques. As a result, these models could not establish bullet-resistant armor, such as TwaronÒ, DyneemaÒ, SpectraÒ, and a quantitative relation among material properties, manufacturing ZylonÒ. process, fabric micro-geometry, and ballistic performance. Fabric penetration resistance is determined not only by fiber In order to improve numerical model accuracy, a sub-yarn physical properties, such as strength, modulus, density, viscosity micro-scale explicit digital element algorithm has been developed and thermal properties, but also by fabric structural geometry. How for numerical simulation of the ballistic impact and the penetration of textile fabrics. The digital element method (DEM) was originally developed to simulate textile processes and to determine textile * Corresponding author. Tel: þ1 785 532 7181; fax: þ1 785 532 7057. fabric micro-geometries [1–5]. In this model, a yarn is discretized as E-mail address: [email protected] (Y. Wang). an assembly of digital fibers. A digital fiber is modeled as a rod 0734-743X/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijimpeng.2009.10.009 Y. Wang et al. / International Journal of Impact Engineering 37 (2010) 552–560 553 to-filament interaction and projectile-to-filament interaction cannot be modeled. As a result, the effect of tow or yarn micro- geometry on the ballistic resistance cannot be analyzed. With the advent of modern ballistic fibers, scientists began to develop computational tools to analyze the penetration resistance performance of textile fabrics made from these fibers. Generally speaking, the research can be divided into two approaches. In one approach, fabrics are modeled as a homogenous continuum. The second approach uses a more detailed geometric representation in which tows (or yarns) are represented as a homogenous continuum. A fabric is then an assembly of tows (or yarns) with a specific pattern. Fig. 1. Roylance model. Numerous models using the homogeneous continuum fabric assumption have been developed since the 1970s. Some repre- sentative models include: a homogeneous and isotropic plate element chain. When distance between two digital fibers is smaller which deforms into a straight sided conical shell when impacted by than fiber diameter, a contact element between them is established. a projectile (Vinson and Zukas [6], 1975, and Taylor and Vinson [7], The textile process is modeled as a quasi-static non-continuum 1990); a two dimensional isotropic membrane (Phoenix and Porwal mechanics problem with boundary conditions. In this paper, [8], 2003); an anisotropic membrane (Simons et al. [9], 2001); use a computer tool, based upon an explicit digital element algorithm, of a system of linear springs to represent continuum behaviour is developed for fabric dynamic analysis. It is used to simulate fabric (Walker [10], 1999); and a visco-elastic continuum with rate response to impact and ballistic penetration. Numerical results are dependent failure (Lim et al. [11], 2002) . While all of these efforts compared to results from fabric impact and ballistic tests. report reasonable success when compared with experiment Comparisons indicate good agreement between digital element results, these approaches are inherently limited as they cannot prediction and experimental results. account for important details such as yarn-to-yarn and projectile- to-yarn interaction, which has been shown to influence the textile 2. Background ballistic performance (Briscoe and Motamedi [12], 1992, and Bhatnagar [13], 2006). Recent efforts (King et al. [14], 2005, and Textiles are comprised of many filaments, arranged in bundles, Boljen and Hiermaier [15], 2006) have resulted in multi-scale called a yarn. Yarns are organized in tows. The tows are assembled formulations that account for the micro-structural aspects of into fabric in specific patterns through weaving or braiding a textile within a membrane formulation. processes. The level of geometric representation of the numerical A more detailed geometric approach started with the pioneer- model dictates the resolution of the numerical results. If a fabric is ing work of Roylance and his coworkers [16]. In their model, a 2-D considered as a continuum, details of tow-to-tow interaction and woven fabric is simplified as a 2-D fiber element network, as shown projectile-to-tow interaction cannot be modeled. As a result, the in Fig. 1. Fiber elements are pin-jointed at crossover points. effect of fabric patterns on ballistic resistance cannot be analyzed. If Therefore, it is commonly called a pin-joint model. Longitudinal a tow or a yarn is represented as a continuum, details of filament- properties of fiber elements are defined by fiber/yarn modulus and Fig. 2. Concept of digital element simulation [3–5]. Download English Version: https://daneshyari.com/en/article/778712 Download Persian Version: https://daneshyari.com/article/778712 Daneshyari.com.