The Effect of Shot Dependency on Composite Materials Subject to Ballistic Testing
[Technical Report, Master's Thesis]
AIR FORCE INSTITUTE OF TECHNOLOGY WRIGHT-PATTERSON AFB OH
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Ballistic analysis was performed on four common composite armor materials 3k standard modulus plain weave carbon fiber, 8HS satin weave S-glass fiber, plain weave Kevlar KM2 600 Denier fiber, and Spectra Shield 4232 ultra-high molecular weight polyethylene to determine shot dependency based upon shot-to-shot impact distance, degree of penetration from the initial impacts, and the delamination effects from the initial impact. The primary measure of ballistic performance was the projectile velocity which represents a 50 probability of penetration, Vso- This velocity was determined using a three-phase optimal design test method with an average of twelve shots per test. Delamination was assessed via visual inspection and the tap test. All plates were 0.25 inches thick and impacted at 0 obliquity from a 0.5-inch-diameter hardened steel ball bearing fired from a nitrogen gas gun. Additionally, an ensemble regression analysis of available ceramic armor data was performed to model ballistic performance. The experimental study found no statistically significant increase in performance for the materials tested. The only shot dependency with statistical significance was a 1 - 2 decrease of the ballistic limit for carbon fiber plates with a second impact one and two projectile diameters away. The regression ensemble proved capable of predicting the ballistic limit with an average error of 6.5. The research recommends additional investigations into the ductility of composite materials to predict delamination updates to MIL-STD-662F and refinement of advanced modeling techniques in ballistic testing.