STRESS STRAIN RELATIONSHIPS IN ULTRA-HIGH MOLECULAR WEIGHT POLYETHYLENE FIBERS UNDER BALLISTIC LOADI

Lt Col Matthew Walker, Canadian Army

Ultra-High Molecular Weight Polyethylene (UHMWPE) fibers are commonly used in body armor systems, alone or in combination with ceramic inserts, as ballistic protection against high velocity projectiles. Under dynamic loading conditions the fibers are extremely strong in tension, but the extreme pressures created at impact by ojive shaped projectiles can cause premature failure before additional fibers can be recruited to distribute the force. A high-pressure gas gun was used to launch 3/8" spherical projectiles into a sample of 20 layered UHMWPE fiber sheets (at 90 degree offset between layers) to examine the force of impact over time. Load cells were used to measure uniaxial forces along the fibers. Digital Image Correlation software was used to collect strain measurements at the same sampling rate as force measurements to analyze the relationship between stress and strain during impact.