Frag Out! Magazine
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age inflicted in the case of previously used helmets. During the program, it was also important to analyze different aspects of the suspension, resistance of hel- mets to external factors, and the possibility of repairs to allow reusing helmets after long-term exploitation. It was also important to create prototypes to subject them to all types of tests. The amount of necessary work was immense. However, the most important as- pect was to design a completely new helmet shape and adjust it to soldiers' head size. MATERIALS In the 1970s, several concepts of solutions regard- ing materials were considered. The Army Materials and Mechanics Research Center, Watertown, Massachu- setts conducted research concerning 3 materials that could be used to produce new helmets (not only infan- try ones). The selected materials were the following: Ä XP – which was a type of polypropylene film the fibers of which had a directional structure, Ä LMLD (Low Modulus Low Density) – a type of fiber glass Ä DuPont Kevlar 29 – aramid fiber. Except for XP, the materials, which actually were fabrics, required resin or special layer to ensure con- nection in the lamination process. The lamination pro- cess of XP, which was a film, only required high tem- perature and pressure. A set of tests was conducted in order to determine the reasonableness for using a particular material. It was not only durability that mattered, but also the sim- plicity of processing and resistance to external fac- tors, such as water or temperature. XP did not require any additives and, when arranged in layers at differ- ent angles, was a good material itself. LMLD bound during the lamination process with polyester resin was called GRP – Glass Reinforced Plastic. Kevlar could be bound during the lamination process by using phenolic or polyvinyl butyral resin. The results of tests conducted simultaneously to the research of PASGT on the shape of the future in- fantry helmet were published in November 1975. It was determined that all the materials were 30-80% more efficient than M1 with the liner. XP was the most du- rable material, but its processing was very difficult. Even the holes for suspension had to be made at high temperature. GRP was the least durable option and had problems with polyester resin (which, actually, did not perform too well as the binder). Despite the initial assumption that the material would be 100% water- proof, it appeared that GRP had problems with dura- bility when exposed to water. Kevlar 29 seemed to be the most promising choice and the final tests as a part of Personnel Armor System considered only helmets made of Kevlar with basis weight of 11.6 or 9.2 kg/m2 (at the beginning, designers considered the possibili- ty of introducing two systems with different protection levels). SIZES The process of designing a new helmet required data on head sizes. Unfortunately, there was initially no good database. The Ballistic Research Laborato- ry used the anthropometric measurements from 1961 and 1966. Several algorithms were elaborated to cal- culate the approximate size of a head on the basis of its perimeter, length, width, and height. However, such information presented a high margin of uncertainty be- cause there were no indirect measurements while they were essential to prepare molds for several different sizes. Several attempts were made to obtain the lack- ing data. The first method, called biostereophotomet- PASGT infantry soldier helmet with Woodland camouflage cover. www.fragoutmag.com