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Materials
Published in Ever J. Barbero, Introduction to Composite Materials Design, 2017
The best-known polymer fibers are the ones processed from polyamide, called aramid fibers (aromatic polyamide), produced by DuPont [97], Teijin [98], and Akzo Nobel [99] under the trade names Kevlar™, Technora™, and Twaron™, respectively. Aramid fibers are LCP fibers. They have high energy absorption during failure, which makes them ideal for impact and ballistic protection. Because of their low density, they offer high tensile strength-to-weight ratio, and high modulus-to-weight ratio, which makes them attractive for aircraft and body armors. Since aramid fibers are made of a polymer material, they have similar characteristics to the polymer matrices discussed in Section 2.5. They have low compressive strength; they creep, absorb moisture, and are sensitive to ultraviolet (UV) light. Also, their mechanical properties vary with temperature, with the tensile strength at 177∘ $ 177^{\circ } $ C reducing to 75–80% of their room temperature value [54]. Various types of aramid fibers offer different material properties, Kevlar 49 being the most commonly used (Tables 2.3–2.4). Technora fibers overcome some of the weaknesses of aramid fibers, having improved thermal stability; they can be used up to 250∘ $ ^{\circ } $ C if some loss of stiffness and up to 50% loss of strength can be tolerated.
Self-Centering Structures Against Earthquakes: A Critical Review
Published in Journal of Earthquake Engineering, 2023
Cheng Fang, Canxing Qiu, Wei Wang, M. Shahria Alam
The maximum effective deformation capacity of these members depends on the yield strain of the PT tendons which should have sufficient elastic deformation. Apart from high-strength steel which was mainly considered in the early days (e.g. Ricles et al. 2002), fiber reinforced polymer (FRP) composite tendons are currently the mainstream tensioning elements because of the relatively large available elastic strain (Attari, Amziane, and Chemrouk 2012; Banibayat 2011; Hensher 2016). Table 1 summarizes the basic properties of some typical types of FRP tendons. Among these, Technora is a commercialized aramid with the largest elastic or fracture strain. Basalt FRP (BFRP) and Glass FRP (GFRP) are also popular candidates which have smaller fracture strains but their cost is lower. Carbon FRP (CFRP) is less considered in SC members because of the limited fracture strain. The mean fracture strains of these FRP tendons range from 1.5% and 3.8%, with a standard deviation of around 0.15 ~ 0.2. Chou and Chen (2015) examined the cyclic response of SC braces using either high-strength steel tendons, GFRP tendons, or CFRP tendons as tensioning elements, and the potential failure modes of the members are discussed.
Soft body armour development by silica particle based shear thickening fluid coated p-aramid fabrics
Published in The Journal of The Textile Institute, 2019
Abhijit Majumdar, Animesh Laha, Debarati Bhattacharjee, Ipsita Biswas, Sanjeev Verma
Multiple layers of high-performance fabrics are used to prepare soft body armours (Srivastava, Majumdar, & Butola, 2012). Researchers working in the area of armour materials are relentlessly trying to reduce the weight of armour without compromising with safety of the wearer. Use of high-performance fibres like aramid (Kevlar, Technora, Twaron, etc.) and ultra-high molecular weight polyethylene or UHMWPE (Dyneema, Spectra, etc.) and selection of proper fabric structure (weave and thread density) are essential for this (Bajaj and Sriram, 1997; Sockalingam, Chowdhury, Gillespie, & Keefe, 2017). Researchers have coated the fabric with natural rubber (Ahmad, Ahmad, Salleh, & Samsuri, 2008; Hassim, Ahmad, Ahmad, Samsuri, & Yahya, 2012) and shear thickening fluid (STF) (Hassan, Rangari, & Jeelani, 2010; Kang, Kim, & Hong, 2012; Wagner & Brady, 2009) to enhance the energy absorption during impact. Shear thickening fluid is a non-Newtonian fluid consisting of a dispersed phase like silica nano-particles and a dispersion medium like polyethylene glycol (PEG) (Lee & Wagner, 2006; Srivastava, Majumdar, & Butola, 2011).
Analysis of thermal comfort properties of fabrics for protective applications
Published in The Journal of The Textile Institute, 2018
Mustafa Ertekin, Gözde Ertekin, Arzu Marmaralı
The term ‘aramid’ is designated for the fibres of the aromatic polyamide type in which at least 85% of the amide linkages (─CO─NH─) are attached directly to the two aromatic rings (Figure 1(a,b)). Meta-aramid fibre, poly(m-phenylene isophthalamide) (MPDI) have low flammability and have been found to be self-extinguishing when removed from the flame. They have moderate tenacity and low elasticity modulus but excellent resistance to heat. Para-aramid fibres exhibit no melting point, high limiting oxygen index for combustion, excellent structural integrity at elevated temperatures, and a high strength to weight ratio. The combination of high strength, non-flammability and high temperature resistance of the para-aramid fibre makes it suitable for thermal protective applications such as car racing, high-risk industries and army. The commercial products include Kevlar® by DuPont, Twaron® and Technora® by Teijin.