Tensile Properties of Dyneema SK76 Single Fibers at Multiple Loading Rates Using a Direct Gripping Method

Abstract

Ultrahigh molecular weight polyethylene (UHMWPE) fibers such as Dyneema and Spectra are seeing more use in lightweight armor applications due to higher tensile strength and lower density compared to aramid fibers such as Kevlar and Twaron. Numerical modeling is used to improve the design of fiber-based composite protective systems. Material response such as tensile stress-strain of different constituents of composites must be studied under experimental conditions similar to strain rates experienced during ballistic events. UHMWPE fibers are difficult to grip by adhesive methods typically used for other fibers due to low surface energy. Based on previous studies, the ability to grip UHMWPE fibers using traditional adhesive methods is dependent on fiber diameter and is limited to smaller diameter fibers which could affect reported stress values. To avoid diameter restrictions and surface energy problems, a direct gripping method has been used to characterize Dyneema SK76 single fibers at quasistatic, intermediate, and high strain rates of 0.001, 1, and 1,000 s -1 , respectively. In an effort to understand the effect of defect distribution along a fiber on its tensile response, multiple gage length samples were studied at the different strain rates. In this paper, the dependence of fiber diameter and gage-length on failure strength is discussed as well as success rate of failures in the gage section with this gripping technique. A comparison of the tensile properties to previous studies is also explored in this study.

Synthesis and characterization of UHMWPE nanocomposite fibers containing carbon nanotubes coated with a PVP surfactant layer

“…Both Spectra and Dyneema are produced from ultra‐high‐molecular‐weight polyethylene (UHMWPE), a thermoplastic polymer with a strong linear structure and a very high molecular weight (3–6 million g/mol). Because of the highly crystallized structure and relatively low density, fibers produced from UHMWPE are lightweight and exhibit high tensile modulus . However, applications of these fibers in structural composites have been limited by undesirable properties such as creep under static conditions and poor shear modulus and strength .…”

A new method for tensile testing UHMMPE single fibers at high temperatures and strain-rates

“…The 5 th and 6 th columns show the number and success rates if the higher than average failure strength fibers are removed from the calculations. The last column shows the grip success rates for Sanborn, et al [11] for strain-rates conducted in their study.. Table 6. Comparison of the uncorrected and corrected average strain to failure values and associated standard deviations observed in this study at 20 °C and those by Sanborn, et al [11] Sandborn's experiments utilized 10 specimens per strain rate.…”

“…1. Maintaining fiber alignment within the yarn is crucial to prevent fiber entanglements and to allow the extraction of single fibers [11]. For this reason, the yarn was clasped with tape at its cut locations to prevent the bulk yarn from splaying while not hindering the separation of single fibers from the yarn.…”

“…The improved fiber grip design used here (see Fig. 10) was based on grips used by Kim and Sanborn [9][10][11], where their grips consist of a base and a removable grip top that together sandwich the single fiber specimen. The gripping pressure is created by tightening two screws connecting the top and bottom halves.…”

“…A combination of adhesive and pressing between rubber tabs has had reported success, however, only a small numbers of tests were performed [4]. For poly(p-phenylene terephthalamide), commonly known as aramid, fibers, grips that minimize slippage have been developed to directly grip fibers between two tabs of poly(methyl methacrylate) [9,10], and the same design using polycarbonate tabs has shown to be successful for UHMMPE single fibers [11]. However, the gripping tabs in these designs are recessed from the grip edge, which prevents access to the gauge length of the fiber for conducting temperature-dependence experiments.…”