No significant strength decrease was noticed even after
200-h treatment in the 5-layer group. For the 5-layer composites,
greater amount of fibre, matrix as well as interface
are involved compared with that of the 2-layer samples, but
the damaged components is only limited on the thinner top
part of the material, the effect of the UV radiation would
be covered by the residual material strength, thus no evident
change of tensile strength was revealed.
Fig. 2 illustrates the scanning electron microscopy photographs
of the laminate surfaces before and after 200-h
UV treatment.