Helmet-Riding to the Next Generation

A helmet is a type of head protection that is worn on the head. By decreasing the impact of a force or collision to the head, a helmet seeks to lessen the risk of significant head and brain injuries. The shell, EPS liner, Comfort liner, Cheek pads, Visor, and Retention or closing mechanism are the different sections of a helmet. The outer shell of a motorcycle helmet can be made lighter and more comfortable by using materials that reduce weight and absorb energy. Metal foams are a type of cellular material that has a number of fascinating qualities, including high stiffness and low specific weight, as well as effective energy absorption. These distinct features make them suitable for a wide range of applications, from car bumpers to aircraft crash recorders. Keywords: Helmet, Material Selection, CFRP, Bluetooth

Characterization and Spectroscopic Applications of Metal Foams From New Lightweight Materials

Lightweight materials such as metallic foams possess good mechanical, chemical, and physical properties, which make them suitable for a wide range of functional and structural applications. Metal foams have recently gained substantial interest in both industry and academia due to their low cost, thermal conductivity, high working temperature, vibration damping, specific mechanical properties, energy absorption, and heat resistance. The use of metal foams on a large scale and successful applications depend on a detailed understanding of their characteristic properties. Metallic foams are characterized by the morphology of the porous cells (size and shape, open or closed, macro and micro), pore topology, relative density, properties of the pore wall, and the degree of anisotropy. This contribution focuses on x-ray diffraction, Fourier transform infrared (FT-IR), and Raman spectroscopic applications used for the characterization of metal foam, and also a brief of the most important applications, including a significant number of examples given.

Direct Pore-Scale Simulations of Fully Periodic Unit Cells of Different Regular Lattices

Open-cell metal foams are known for their superior heat dissipation capabilities. The morphological, pressure-drop and heat transfer characteristics of stochastic metal foams manufactured through traditional 'foaming' process are well established in the literature. Employment of stochastic metal foams in next generation heat exchangers, is however, challenged by the irregularity in the pore-and fiber-geometries, limited control on the pore-volume, and an inherent necessity of a bonding agent between foam and heat source. On the other hand, additive manufacturing is an emerging technology that is capable of printing complex user-defined unit cell topologies with customized fiber shapes directly on the heated substrates. Moreover, the user-defined regular lattices are capable of exhibiting better thermal and mechanical properties than stochastic metal foams. In this paper, we present a numerical investigation on fully periodic unit-cells of three different topologies, viz. Tetrakaidecahedron (TKD), Rhombic-dodecahedron (DDC), and Octet with air as the working fluid. Pressure gradient, interfacial heat transfer coefficient, friction factor, and Nusselt number are reported for each topology. Rhombic-dodecahedron yielded in the highest average interfacial heat transfer coefficient whereas Octet incurred the highest flow losses. Pore diameter, defined as the maximum diameter of a sphere passing through the polygonal openings of the structures, when used as the characteristics length scale for the presentation of Nusselt number and Reynolds number, resulted in a single trendline for all the three topologies.

Various Trade-Off Scenarios in Thermo-Hydrodynamic Performance of Metal Foams Due to Variations in Their Thickness and Structural Conditions

The long standing issue of increased heat transfer, always accompanied by increased pressure drop using metal foams, is addressed in the present work. Heat transfer and pressure drop, both of various magnitudes, can be observed in respect to various flow and heat transfer influencing aspects of considered metal foams. In this regard, for the first time, orderly varying pore density (characterized by visible pores per inch, i.e., PPI) and porosity (characterized by ratio of void volume to total volume) along with varied thickness are considered to comprehensively analyze variation in the trade-off scenario between flow resistance minimization and heat transfer augmentation behavior of metal foams with the help of numerical simulations and TOPSIS (Technique for Order of Preference by Similarity to Ideal Solution) which is a multi-criteria decision-making tool to address the considered multi-objective problem. A numerical domain of vertical channel is modelled with zone of metal foam porous media at the channel center by invoking LTNE and Darcy–Forchheimer models. Metal foams of four thickness ratios are considered (1, 0.75, 0.5 and 0.25), along with varied pore density (5, 10, 15, 20 and 25 PPI), each at various porosity conditions of 0.8, 0.85, 0.9 and 0.95 porosity. Numerically obtained pressure and temperature field data are critically analyzed for various trade-off scenarios exhibited under the abovementioned variable conditions. A type of metal foam based on its morphological (pore density and porosity) and configurational (thickness) aspects, which can participate in a desired trade-off scenario between flow resistance and heat transfer, is illustrated.

Experimental thermal performance comparison of pure and metal foam-loaded PCMs

The thermal performance of latent heat thermal energy storage (LHTES) systems considerably depends on thermal conductivity of adopted phase change materials (PCMs). To increase the low thermal conductivity of these materials, pure PCMs can be loaded with metal foams. In this study, the melting process of pure and metal-foam loaded phase change materials placed in a rectangular shape case is experimentally investigated by imposing a constant heat flux at the top. Two different paraffin waxes with melting point of about 35°C are tested. The results obtained with pure PCM are compared with those achieved from the use of PCM combined with two different porous metals: a 10 PPI aluminum foam with 96% porosity and a 20 PPI copper foam with 95% porosity. The results demonstrate how metal foams lead to a significant improvement of conduction heat transfer reducing significantly the melting time and the temperature difference between the heater and PCM.