We continue our discussion of polymers in sports equipment by looking at football helmets. The well-publicized dangers of head injuries have put helmet design back in the forefront of sports equipment manufacturers. Modern day football helmets bear little resemblance to the original leather helmets first introduced in the early 1900s. These leather helmets had no face guards, little padding, and were primarily used to protect the players’ ears. In the late 1930s, plastic helmets were introduced, which incorporated the chin strap for the first time. In the 1940s, the first face guards made their appearance, although they were much more minimal than the modern face guards seen today.
Material Composition of a Football Helmet
The mechanical requirements of football helmets requires a material that is lightweight, tough, and exhibits good impact strength. Most modern helmets use polycarbonate for the outer shell. Polycarbonate is a high impact resistant polymer that can be injection molded, painted, and can maintain its properties when subjected to cold temperatures, an important feature for teams playing in the northern states. Less expensive helmets sometimes use acrylonitrile-butadiene-styrene (ABS) copolymer, another impact resistant material.
The padding in helmets, critical for absorbing and dampening impact loads, is often made from nitrile-based foam, and reinforced with polyethylene foam. The pore size and chemistry of the foam will affect its viscoelastic response (modulus vs. frequency response), which is the most important behavior for a helmet application, so proper testing of potential materials is important, often requiring dynamic mechanical analysis.
Minimizing Impact Load
In addition to material selection, helmet design plays an important role in its ability to minimize direction transmission of impact load from the helmet to the athlete’s brain. Some helmet designs contain a hexagonal-shaped cutout near the forehead of the helmet. This cutout is a cantilever system which is intended to absorb some of the impact force.
Researchers are also considering integrated helmet-shoulder pad designs to further dissipate impact loads from the head down into the body. Accelerometers built into the helmets provide side-line monitoring of impact loads in players.
Tunaendelea na majadiliano yetu juu ya polima katika vifaa vya michezo kwa kuangalia kofia za chuma za mpira wa miguu. Hatari za majeraha ya kichwa ambazo zimetangazwa sana zimerudisha muundo wa kofia za chuma kwenye nafasi ya kwanza kati ya watengenezaji wa vifaa vya michezo. Kofia za mpira wa miguu za kisasa zinafanana kidogo na kofia za ngozi za awali zilizoletwa kwa mara ya kwanza mwanzoni mwa miaka ya 1900. Kofia hizo za ngozi hazikuwa na kinga za uso, hazikuwa na vifuniko vingi, na zilitumiwa hasa kulinda masikio ya wachezaji. Katika miaka ya 1930 na 1920, kofia za chuma za plastiki zilitengenezwa, na kwa mara ya kwanza, vifungo vya ngozi vilitengenezwa. Katika miaka ya 1940s, walinzi wa uso wa kwanza walionekana, ingawa walikuwa wachache sana kuliko walinzi wa uso wa kisasa wanaoonekana leo. Mchanganyiko wa vifaa vya kofia ya mpira wa miguu Mahitaji ya mitambo ya kofia za mpira wa miguu yanahitaji nyenzo ambayo ni nyepesi, ngumu, na inaonyesha nguvu nzuri ya athari. Kofia nyingi za kisasa hutumia polycarbonate kwa ajili ya ganda la nje. Polycarbonate ni high athari sugu polima ambayo inaweza kuwa sindano umbo, rangi, na inaweza kudumisha mali yake wakati chini ya joto baridi, kipengele muhimu kwa timu kucheza katika majimbo ya kaskazini. Vifaa vya kujikinga vya chuma vya hali ya juu vinaweza kutengenezwa kwa kutumia acrylonitrile-butadiene-styrene (ABS) copolymer, ambayo ni nyenzo nyingine ya kuhimili athari. Padding katika kofia za chuma, muhimu kwa ajili ya kunyonya na dampening athari mizigo, ni mara nyingi kufanywa kutoka nitrile-msingi povu, na kuimarishwa na polyethylene povu. Ukubwa wa pore na kemikali ya povu itaathiri majibu yake ya viscoelastic (moduli dhidi ya majibu ya mzunguko), ambayo ni tabia muhimu zaidi kwa matumizi ya kofia ya chuma, kwa hivyo upimaji sahihi wa vifaa vya uwezekano ni muhimu, mara nyingi inahitaji uchambuzi wa nguvu. Kuondoa mzigo wa athari: Kwa kuongezea uteuzi wa vifaa, muundo wa kofia ya chuma una jukumu muhimu katika uwezo wake wa kupunguza mwelekeo wa usambazaji wa mzigo wa athari kutoka kofia ya chuma hadi ubongo wa mwanariadha. Baadhi ya miundo ya kofia ya chuma ina kipande cha umbo la pembe sita karibu na paji la uso wa kofia ya chuma. Hii cutout ni mfumo cantilever ambayo ni lengo la kunyonya baadhi ya nguvu ya athari. Watafiti pia wanafikiria miundo ya kifuniko cha bega cha kofia ya chuma ili kuondoa zaidi mizigo ya athari kutoka kichwa hadi chini kwenye mwili. Accelerometers kujengwa katika kofia za chuma kutoa upande-line ufuatiliaji wa mzigo wa athari katika wachezaji.