13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Strain Rate Effect on the Failure Behavior of Kevlar 49 Fabric and Single Yarn Deju Zhu1,*, Barzin Mobasher2, Subramaniam D. Rajan2 1 College of Civil Engineering, Hunan University, Changsha, 410082, China 2 School of Sustainable Engineering & the Built Environment, Arizona State University, Tempe, 85287, USA * Corresponding author: dzhu@hnu.edu.cn Abstract: High strength woven fabrics are ideal materials for use in structural and aerospace systems where large deformations and high-energy absorption are required. Their high strength to weight ratio and ability to resist high-speed impacts enables them to be more efficient than metals in many applications, including ballistic armors, propulsion engine containment systems and fabric-reinforced composites. In order to facilitate the design and improvement of such applications, this study investigates the mechanical behavior of Kevlar 49 fabric and single yarn under quasi-static and dynamic tensile loadings. The experimental results show that the fabric exhibits non-linear in tension, and can deform up to 20% before complete failure under quasi-static loading. The fabric has identical Young’s modulus in warp and fill directions, but has different crimp strain, tensile strength and ultimate strain. The sample size has little effect on the mechanical properties of the fabric. The dynamic tensile behaviors of the fabric and single yarn were investigated at strain rates from 25 to 170 s-1 by using a high rate servo-hydraulic testing machine. Results show that their dynamic material properties in terms of Young's modulus, tensile strength, maximum strain and toughness increase with increasing strain rate. Keywords: Fabrics, Dynamic, Strain rate, Kevlar 49 1. Introduction High strength woven fabrics are ideal materials for use in structural and aerospace systems where large deformations and high energy absorption are required. Their high strength to weight ratio and ability to resist high speed impacts enables them to be more efficient than metals. Materials loaded at high strain rates can exhibit mechanical characteristics that are different from those obtained under quasi-static loading. High strain rate applications are quite varied and include structural, military, aerospace, and sports disciplines. Aramid and other high strength fibers and fabrics have been studied extensively in a wide range of applications, creating a demand for numerical modeling of fibers, yarns, and fabrics. While quasi-static tensile strength data for the single fibers is available, results cannot be extrapolated and scaled up for yarns consisting of many fibers, woven, knitted, or bonded fabrics with a 2-D or 3-D microstructure. Furthermore, the strain rates observed in static experiments is not in the same order of magnitude as those observed in ballistic applications [1]. Five types of testing systems are commonly used in generating the rate dependent material data: the conventional screw drive load frame, servo-hydraulic system, high rate servo-hydraulic system, impact tester and Hopkinson bar system. However, the experimental techniques to generate stress-strain data at the medium strain rates in the range of 1~100 s-1 are not well established [2]. Two types of equipment have been used to generate data in this strain rate range: high rate servo-hydraulic testing machines [3-5] and drop-weight impact machines [6, 7]. The primary objective of our research is to investigate the effects of gage length and strain rate on the mechanical properties of Kevlar 49 fabric and single yarn, as a part of the project on explicit finite element modeling of multi-layer composite fabric for gas turbine engine containment systems [8-12]. In the next section we present the experimental procedure and results of fabric and single
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