A Preliminary Study of the Effect of Shot Blasting upon the Ballistic Characteristics of the M1 Steel Helmet.
WATERTOWN ARSENAL LABS MA
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Shot blasting experiments were conducted upon a gruop of helmets using roughly spheroidal chilled steel shot of No. 14 mesh at an air pressure of 45 pounds per square inch. It was found that shot blasting the entire exterior surface of the helmet has an adverse effect upon the ballistic properties as determined with caliber .45 ball ammunition, reducing the ballistic limit and causing brittle failures. Shot blasting the entire interior surface of the helmet or shot blasting both the interior and exterior surfaces produces no appreciable change in the ballistic properties as compared to the as-received helmets. It is believed that any treatment which will leave the interior surface of the helmet in tension will adversely affect the ballistic properties. The original residual stresses induced by cold forming are generally tensile on the exterior surface of the helmet and compressive on the interior surface and are thus favorably disposed to resist ballistic attack, although unfavorably disposed from the viewpoint of resistance to service cracking.
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