Effects of spacing and ply blocking on the ballistic resistance of UHMWPE laminates

It is commonly claimed that ultra-high molecular weight polyethylene (UHMWPE) laminates offer high energy absorption during projectile impact with a cross-ply configuration. In this study, we explored alternative configurations with the aim of achieving better ballistic resistance than that of the cross-ply architecture. The UHMWPE laminates were fabricated from Endumax (R) cross-ply SHIELD XF23 using a hot press machine and material properties were obtain from Endumax (R) unidirectional (UD) tape TA23 coupon specimens. A solid steel sphere was used as the projectile. It was found that thinner laminates have higher the specific ballistic limit suggesting that it is more effective to deploy multiple stacks of thin laminated panels spaced apart than to bond all the laminas to form a single thick laminate. Experiments confirmed that while the multiple laminate systems always outperformed a single laminate comprising the same number of laminas, it was also best not to space the laminates apart. When simply stacked without spacing, the multi-laminate arrangement significantly enhanced the ballistic performance (about 10% increase in ballistic limit over the single panel). Adjacent laminates in the multi-laminate system were then rotated 45 degrees relative to each other and then bonded together to form a single laminate with multiple blocks of similarly oriented laminas. This ply block configuration also had higher ballistic limit than the single cross-ply laminate for thin laminates but showed no advantage for thick laminates.