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Transverse impact response of a linear elastic Kevlar® KM2 fiber yarn was determined at various striking speeds from Hopkinson bar and gas gun experiments incorporated with high-speed photography techniques. Upon transverse impact, a triangle shape was formed in the fiber yarn. Both longitudinal and transverse waves were produced and propagated outwards the fiber yarn. Both the angle of the triangle and Euler transverse wave speed vary with striking speeds. The relationship between the Euler transverse wave speed and the striking speed was determined. The transverse impact response of the fiber yarn was also analyzed with a model, which agrees well with the experimental results. The model shows that the longitudinal wave speed is critical in the ballistic performance of the fiber yarn. At a certain striking speed, a higher longitudinal wave speed produces a higher Euler transverse wave speed, enabling us to spread the load and dissipate the impact energy faster, such that the ballistic performance of the fiber yarn is improved. [ABSTRACT FROM AUTHOR]

Dynamic crack propagation across a perpendicular interface in a glass specimen was investigated to understand the interaction between the crack and the interface under impact loading. The glass specimen was composed of two glass plates in an edge-to-edge configuration with an adhesive layer in between. One of the plates had a notch for a plastic projectile to strike. A single crack developed from the notch tip, and propagated perpendicularly into the interface. The patterns of crack propagation across the interface depend on the adhesive conditions on the interface. Within a range of impact speeds, the crack is arrested at the interface without any adhesive. The crack passes across a firmly bonded interface with little obstruction by the interface. The crack branches into multiple cracks after it passes through a thicker interface filled with adhesive. Projectiles having higher kinetic energies cause more severe crack branching after the crack extends into the second glass plate [ABSTRACT FROM AUTHOR]

Glass impact experiments were designed at three different scales-0.22-cal, 0.375-cal, and 0.50-cal-named after the diameter of the bullets. Four experimental series were conducted at the three scale sizes: (1) Lexan®-only experiments; (2) monoblock glass experiments; (3) single impact bonded glass experiments, and (4) multi-hit experiments. The experiments were conducted to obtain residual velocity Vr as a function of impact (striking) velocity Vs, including sufficient partial penetrations to calculate a ballistic limit velocity V50. The Vs - Vr data were fit to the Lambert equation to obtain another estimate of V50. The objective of the experiments was to investigate whether a time dependency exists in glass damage/failure for ballistic experiments, and if so, quantify this dependence. No scale effect was observed in experimental results for the Lexan®-only experiments. But a variety of scale effects were observed in the glass impact experiments, suggesting that failure is time dependent within the timeframe of ballistic events [ABSTRACT FROM AUTHOR]