Experimental and numerical study of the response of flexible laminates to impact loading

Fabrics and flexible laminates comprising highly oriented polymers possess high impact resistance and are often used in flexible armour applications. This study presents an idealized computational model for flexible [0°/90°] polyethylene fiber-reinforced laminates and show how the model can simulate actual impact tests conducted on the laminates. As these materials are viscoelastic, accurate modeling of their impact and perforation responses requires the formulation of constitutive equations representing such behavior. The material is idealized as networks of one-dimensional pin-jointed fiber elements defined by viscoelastic constitutive relations. Three-element viscoelastic Zener models are used as they are simple yet sufficient to account for the effects of intermolecular and intramolecular bonds, as well as viscous slippage between molecular chains, on the mechanical properties of oriented polymeric fibers. The effects of delamination in laminates are also taken into consideration by modeling flexible laminates as two fiber network layers bonded to each other at corresponding element cross-over points in the adjacent layers. Inter-ply bonding is represented by infinitesimal rigid links which break when the inter-ply bond strength is exceeded resulting in delamination between the plies. Predictions of residual velocity, development of deformation and delamination correlate well with experimental results.