High-velocity impact loading of thick GFRP blocks

Abstract
In previous depth of penetration experiments with tungsten long rod projectiles was found that the ballistic resistance of a relatively thick-up to the penetrator length-glass fibre reinforced plastic block grows with increasing penetration depth. This penetration behaviour significantly differs from that of other inert armour materials. Until now, no significant difference between unconfined and totally confined GFRP configurations bas been found. Newest experiments with up to semi-infinite thick GFRP blocks show a change in the penetration process: For thicknesses significantly higher than the penetrator length the protective power may saturate. During the late penetration phase the shortening and deceleration of the projectile induce a change of penetration mechanism from erosion to rigid body penetration. Additionally, the projectile may break into several individually tumbling parts. Reflected tension waves and, probably, pyrolysis effects may cause increasing precursory damage. These effects together are likely to explain the reduction of the ballistic resistance increase during the late penetration phase. Based on these experimental results the published working hypothesis on the governing mechanism of the GFRP penetration behaviour had to be completed. A new approach based on a hyperbolic tangent function seems to satisfactorily describe the observed thickness dependent phenomena.