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Lightweight Thermoset Foams in Automotive Applications
Published in Omar Faruk , Jimi Tjong , Mohini Sain, Lightweight and Sustainable Materials for Automotive Applications, 2017
Numaira Obaid, Mark T. Kortschot, Mohini Sain
Polymeric foam contains entrapped air that absorbs sound energy and converts it into heat, allowing vibrations to be dissipated effectively. One of the most important parameters controlling the sound absorption capability of a foam is its resistance to air flow. If air flow is restricted, the foam has better sound absorption [41–43]. Air movement depends on the volume fraction, size, and connectivity of the pores. Low-density foams have a larger fraction of air and a lower resistance to air movement, and thus, have a lower sound absorption. The cell size and arrangement also have an important effect on sound absorption. When a sound wave hits a rigid surface, it is reflected; however, in a porous structure, the sound waves are continually reflected and refracted by the cell walls, and the frictional losses eventually dampen the wave [44]. A smaller cell size encourages more frequent propagation of the sound waves from the cell wall to entrapped air, and is known to increase sound absorption. In addition, smaller cells are less connected to each other and increase resistance to air flow. One study showed that decreasing cell size of polyurethane foams using nano-silica as a nucleating agent resulted in improved sound absorption [45]. Asadi and Ohadi confirmed this result by showing that better dispersion of the nano-silica, which resulted in smaller cell sizes, increased the sound absorption coefficient of the foams, even when the volume fraction of filler was fixed [46].
Polymeric Foams
Published in Kathleen Hess-Kosa, Building Materials, 2017
What differentiates plastics from polymeric foams? Simply stated, “A polymeric foam is a gas-filled plastic.” In many cases the addition of a gas or gases can cause the plastic to expand as much as 100 times its original volume. The foaming process involves one, or a combination, of the following: Gaseous foaming—nitrogen, air, carbon dioxide, and/or an air/helium mixtureLiquid foaming—hydrochlorofluorocarbons (HCFC), hydrofluorocarbons (HFC), and other chlorofluorocarbon substitutesChemical foaming—mineral or chemical usually solids, that are able to decompose when heated to liberate large amounts of gas such as nitrogen, carbon dioxide, carbon monoxide, and hydrogen The mineral foaming agents are generally salts (e.g., ammonium bicarbonate) and weak acids.The chemical foaming agents are organic, consisting of one of several chemicals such as azo and diazo compounds, N-nitroso compounds, sulfonyl-hydrazides, azides, triazines, sulfonyl semicarbazides, urea derivatives, guanidine derivatives, and esters.
Fabrication Processes
Published in Manas Chanda, Plastics Technology Handbook, 2017
Rigid urethane foams have outstanding thermal insulation properties and have proved to be far superior to any other polymeric foam in this respect. Besides, these rigid foams have excellent compressive strength, outstanding buoyancy (flotation) characteristics, good dimensional stability, low water absorption, and the ability to accept nails or screws like wood. Because of these characteristics, rigid foams have found ready acceptance for such applications as insulation, refrigeration, packaging, construction, marine uses, and transportation.
A modified finite element dummy model of Chinese adult male used for train collision simulations
Published in International Journal of Rail Transportation, 2023
Zhenhao Yu, Shaodong Zheng, Kai Liu, Zhipeng Gao, Longmao Zhao, Lin Jing
Discrete beam elements were used to simulate the mechanical properties of force element structures such as springs, shock absorbers, and energy absorption devices in primary and secondary suspension systems [68]. Aluminium alloy car-body adopts follow-up strengthening material model MAT_3 to characterize its elastoplastic characteristics. The material model of the backrest and cushion of polymeric foam was simulated by MAT_57 and the 7005-aluminium alloy of the seat frame, chassis, and handrail was modelled by MAT_24. The stress–strain curves of the 7005-aluminium alloy and polymeric foam are given in Figure 8 [69]. Due to the high strength and rigidity of the wheelset and rail, the rigid material model was used to save calculation costs. In the collision, the rolling of wheelsets was simplified into translational motion, and the friction coefficient was set as 0.008 [70]. Mechanical parameters related to components of the train and dummy integration model are shown in Table 5 [71].
PolyHIPEs for Separations and Chemical Transformations: A Review
Published in Solvent Extraction and Ion Exchange, 2019
Kathryn M. L. Taylor-Pashow, Julia G. Pribyl
Polymeric foam materials have been studied for a number of applications for decades. A specific type of polymeric foam material, later coined “polyHIPE” has been prepared from high internal-phase emulsion (HIPE) reactions and will be the focus of this review. HIPEs are typically water-in-oil emulsions, in which the dispersed (typically aqueous) phase comprises at least 74% of the emulsion by volume. If the continuous phase is composed of a polymerizable monomer, then in principle the continuous phase can be polymerized to form a solid monolith polymer. Early reports of this technique began in the 1960s; however, these early reports appeared to result in foams with a closed-cell structure, that is, no interconnecting pores. In a 1982 patent issued to Unilever, the concept of an open-celled polyHIPE was demonstrated.[1] The term polyHIPE was filed as a registered trademark of Unilever in the United Kingdom in May 1982.
Evaluation and improvement of crashworthiness for high-speed train seats
Published in International Journal of Crashworthiness, 2018
The high-speed train's seat is made up of cushion, backrest, chassis, frame, handrails and so on. To analyse the collision dynamic for the high-speed train seats, a finite element model of the seat was created using the Altair HyperWorks graphical pre-processor, though some small modifications were performed Using Primer. The metal structures such as frame, chassis and handrails were made by aluminium 7005 and modelled using the material model *MAT_24: PIECEWISE_LINEAR_PLASTICITY, from the LS -DYNA 3D material library for Belytschko-Tsai shell element. The constant stress solid element was employed to model the backrest and cushion structure. The material model of backrest and cushion was defined as *MAT_57: LOW _DENSITY _FOAM). The stress–strain curve of the aluminium 7005 and polymeric foam [12] under LS_DYNA code is defined in Figure 1.