Spall strength of glass fiber reinforced polymer composites

In the present paper results of a series of plate impact experiments designed to study spall strength in glass–fiber reinforced polymer composites (GRP) are presented. Two GRP architectures are investigated—S2 glass woven roving in Cycom 4102 polyester resin matrix and a balanced 5-harness satin weave E-glass in a Ciba epoxy (LY564) matrix. The GRP specimens were shock loaded using an 82.5 mm bore single-stage gas-gun. A velocity interferometer was used to measure the particle velocity profile at the rear (free) surface of the target plate. The spall strength of the GRP was obtained as a function of the normal component of the impact stress and the applied shear-strain by subjecting the GRP specimens to normal shock compression and combined shock compression and shear loading, respectively. The spall strengths of the two GRP composites were observed to decrease with increasing levels of normal shock compression. Moreover, superposition of shear-strain on the normal shock compression was found to be highly detrimental to the spall strength. The E-glass reinforced GRP composite was found to have a much higher level of spall strength under both normal shock compression and combined compression and shear loading when compared to the S2-glass GRP composite. The maximum spall strength of the E-glass GRP composite was found to be 119.5 MPa, while the maximum spall strength for the S2 glass GRP composite was only 53.7 MPa. These relatively low spall strength levels of the S2-glass and the E-glass fiber reinforced composites have important implications to the design and development of GRP-based light-weight integral armor.