This paper examines the development of microstructural damage in a gla
ss-reinforced polymer (GRP) laminate subjected to explosive shock load
ing in water. GRP is commonly used in small naval vessels, and may be
subjected to under-water explosions. In the experiments, the laminates
were exposed to increasing amounts of shock loading produced by under
water explosions. The laminates were backed with either water or air t
o modify the amount of bending experienced under loading, with the air
-backed laminates having the higher amount of bending. Examination of
the GRP microstructure by optical and scanning electron microscopy aft
er shock testing failed to reveal any damage to either the polymer mat
rix or glass fibres when the laminate was backed with water. In contra
st, when the laminate was backed with air, small cracks were produced
in the polymer matrix at low shock pressures. Raising the shock pressu
re above a threshold limit caused complete failure of the laminate by
cracking in the polymer matrix, cracking of the glass fibres, and dela
mination of the glass fibres from the polymer. The differences in the
shock resistance of the water- and air-backed GRP are discussed. Measu
rements of the residual tensile fracture strength of the laminates aft
er shock loading are also presented. The fracture strength of the wate
r-backed laminate was not affected by shock, but the fracture strength
of the air-backed laminate deteriorated with the onset of glass fibre
breakage and delamination in the GRP microstructure.