Applied Sciences, Vol. 12, Pages 12251: Mechanical Performance of Polymer Materials for Low-Temperature Applications

Lightweight constructions have been increasingly used in automotive, shipbuilding, construction, and aerospace industries because using low-density materials reduces the structural weight of products. Adopting low-density materials leads to fuel savings, low carbon footprint, and conservation of natural resources because less material is required for manufacturing consumer goods. Polymers, which are representative lightweight materials, are suitable for replacing conventional metallic steel and alloys because they offer several advantages such as ease of processing, the possibility of obtaining complex shapes, good mechanical strength, durability, and a relatively low price [1].Figure 1 shows the plastic piping systems employed in an icebreaking tanker. In the shipping and offshore industries, lightweight is one of the main issues in reducing payload, reaching high speed, and reducing fuel consumption. Therefore, new materials and related technologies have been adopted; in particular, the use of polymer and composite materials has steadily increased in recent years [2,3,4]. In the transport field, various polymer materials have been extensively adopted in plastic piping systems, such as refrigeration, ballast system, and seawater drain, depending on material characteristics such as chemical resistance, temperature resistance, and flexibility for assembly. Moreover, from the lightweight aspect, researchers have attempted to extensively investigate polymer and composite pipes under low-temperature environments to replace conventional low-temperature metallic steel pipes. A representative application field of polymer and composite materials in low-temperature environments is in pipes for liquefied natural gas, which is stored and transported at −163 °C [5,6]. The growth of natural gas consumption is expected to exceed that of fossil fuels because natural gas has more favorable environmental and practical attributes. In addition, another issue is the Arctic shipping routes. They connect the world’s largest economies in the Atlantic and Pacific Oceans via more profitable, shorter, faster, and thus more environmentally friendly trade routes than conventional shipping lanes. Icebreakers—special-purpose ships designed to move and navigate through ice-covered waters in the Arctic Ocean—have been exposed to risks such as freezing and bursting of pipes in extremely cold regions. Accordingly, setting clear criteria for the application of plastic materials to a pipe system is necessary. In addition, the investigation of material characteristics of polymer materials depending on application environments is required. For these reasons, investigating the mechanical and failure characteristics and confirming them at the design stages is important to adapt to low-temperature environments and ensure the ability of polymer materials to withstand low-temperature conditions from the lightweight aspect.The mechanical behavior of polymers is significantly influenced by the strain rate, according to several research findings from the previous decades. Ebert et al. reported polypropylene’s strain-rate-dependent deformation behavior. The tensile tests were conducted at six different strain rates: (1.15 × 10−3, 1.15 × 10−2, 1.15 × 10−1, 1.15, 1.15 × 102, and 1.15 × 103 s−1). The tensile strength exhibited an increasing trend with the increasing strain rate under the conditions adopted for the strain rate [7]. Fang et al. studied the rate-dependent large deformation behavior of polycarbonate and acrylonitrile–butadiene–styrene (PC/ABS) at crosshead speeds ranging from 1 to 3000 mm/min. The results demonstrated that the strain rate substantially affects the stress–strain relationship of PC/ABS. At lower strain-rate ranges, the necking deformation can be ignored, but not at higher strain rates [8]. Reis et al. examined the impact of temperature and strain rate on the tensile behavior of high-density polyethylene (PE). Experiments were carried out at four distinct constant isothermal temperatures (25 °C, 50 °C, 75 °C, and 100 °C) and five distinct strain rates (7.25 × 10−5, 1.45 × 10−4, 7.25 × 10−4, 1.45 × 10−3, and 7.25 × 10−3 s−1). Their research revealed that temperature and strain-rate dependence significantly impacted rigidity, tensile strength, and ductility. The ultimate tensile strength exhibited a decreasing trend as the temperature and strain rate increased [9]. Vidakis et al. studied the effect of strain rates on thermoplastic polymers processed by fused filament fabrication (FFF), including polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), polyethylene terephthalate glycol (PETG), polyamide6 (PA6), and polypropylene (PP). The mechanical properties of PA6, ABS, and PP 3D-printed samples, including stiffness, yield strength, tensile strength, and toughness, exhibited a low dependence on strain-rate sensitivity. However, PLA appears to be extremely strain-rate sensitive [10]. At room temperature, Nakai and Yokoyama tested the uniaxial compressive response of six commercially available extruded polymers, including ABS, high-density polyethylene (HDPE), polycarbonate (PC), polyoxymethylene (POM), PP, and polyvinylchloride (PVC), at three different strain rates (10−3 s−1, 10−1 s−1, and 1.0 s−1). Except for HDPE and POM, the elastic modulus and strength of the polymers increased significantly with strain rate [11]. Varghese and Murugan investigated the effect of extrusion orientation and strain rate on the mechanical behavior of thermoplastic sheets such as HDPE, ABS, and isotactic polypropylene (i-PP). Specimens cut in three different orientations were subjected to uniaxial tension tests with strain rates ranging from 0.01 to 0.3 s−1. Regardless of their orientations, an increase in strain rate led to an increase in yield strength for all three polymers [12]. Farrokh and Khan investigated the strain-rate sensitivity of yield behavior in a semicrystalline polymer, nylon 101. Different specimens with different designs and geometries were prepared to conduct experiments under different loading conditions such as tension, compression, torsion, and biaxial loading condition. All experiments were conducted at four different strain rates (10−5, 10−4, 10−2, and 1 s−1) at room temperature. The results showed that the mechanical strength increased in proportion to the strain rate [13]. Mulliken and Boyce investigated the strain-rate-dependent elastic–plastic deformation of poly (methyl methacrylate) (PMMA) and PC at strain rates in the range 10−4–104 s−1. The results showed that both the PC and PMMA materials exhibited enhanced rate sensitivity when deformed under high rates of loading compared to their behavior under quasistatic rates of loading. The enhanced rate sensitivity was directly attributed to the restriction of secondary molecular motions [14].Previous research evaluated various polymer materials, including PE, ABS, PLA, PETG, PA6, HDPE, and POM, for their mechanical performance at quasistatic and dynamic strain rates. According to most research findings, the stiffness and strength of polymer materials showed an upward trend with an increasing strain rate. Although the essential mechanical characteristics have been identified accurately, the available information is limited to the mechanical characteristics at ambient and above-ambient temperatures. Amjadi and Fatemi studied the tensile behavior of HDPE, including its temperature and strain-rate effects. To investigate the temperature effect, temperatures of −40, 23, 53, and 82 °C were selected. By increasing the temperatures from −40 °C to 82 °C, the elastic modulus, yield strength, and tensile strength decreased significantly, whereas the elastic modulus and ultimate tensile strength increased linearly [15]. The influence of stress triaxiality, strain rate, and temperature on the mechanical response and morphology of polyvinylidene fluoride (PVDF) was reported by Hund et al. Between −20 °C and 100 °C, the thermoviscoelastic response of the material was investigated at a quasistatic strain rate of 0.005 s−1. In addition, the influence of strain rates (0.005, 0.1, and 1.0 s−1) at room temperature was investigated. The material exhibited a temperature- and strain-rate-dependent behavior in which the stress level increased with the increasing strain rate and decreasing temperature [16]. Richenton et al. examined the uniaxial compressive test on three distinct amorphous commercial polymers: PC, PMMA, and polyamide–imide (PAI). Experiments were conducted at temperatures ranging from −40 °C to 180 °C and strain rates of 0.0001 s−1 up to 5000 s−1. The yield strength was not significantly affected by the quasistatic strain rate condition, but it was significantly affected by the high-strain-rate condition [17]. Rae and Brown investigated the tensile material properties of poly(tetrafluoroethylene) (PTFE) at strain rates in the range 2 × 10−4–0.1 s−1 and temperatures in the range −50–150 °C. Test results at −50 °C showed a significant decrease—approximately threefold—in the failure strain compared to the results in ambient temperature (25 °C) [18].In the aforementioned studies, the mechanical performance and properties of polymer materials in a variety of low-temperature environments were reported. However, most previous research was limited to temperatures up to −50 °C. Even though the mechanical behavior of polymers is sensitive to varying loads and temperatures, studies on the material properties of polymers under low-temperature conditions are insufficient for industrial applications. Rae and Dattelbaum investigated the compressive material properties of PTFE. In this paper, the compression test was conducted at strain rates in the range 10−4–1 s−1 and temperatures in the range −198 °C to 200 °C. The tests were performed by immersing the samples in liquid nitrogen throughout the test. The samples tested at −198 °C all shattered at approximately 35% strain [19]. Although the PTFE polymer material was impregnated with liquid nitrogen (−198 °C) and the compressive test result was reported, it is difficult to obtain a quantitative database of the polymer materials for ABS, PE, and PVDF in low-temperature environments.

In this study, strain-rate-dependent mechanical tests were conducted at low temperatures to determine the effect of temperature on the strength, elastic modulus, fracture strain, and toughness of three different polymer materials used in the ship and offshore industries. Based on their industrial viability, the following polymer candidates were chosen: PE, ABS, and PVDF. Finally, we quantitatively summarized the temperature (25 °C, 0 °C, −50 °C, and −100 °C) and strain-rate (10−4, 10−3, and 10−2 s−1)-dependent properties.

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