ENVIRONMENTAL-STRESS CORROSION OF HYBRID FIBER COMPOSITES

Unidirectional glass/epoxy, carbon/epoxy and glass/carbon/epoxy hybrid laminates (14 glass plies and 2 carbon) were immersed in water, humid air and dilute (0.5 M) sulphuric acid and subjected to various levels of constantly applied tensile stress until rupture occurred. When the liquids were allowed direct access to the cut edges of rectangular strip specimens, and hence to the glass plies, the position of the carbon plies made little difference to the failure time at a given stress. Protecting the cut edges and allowing access only to the major faces resulted in failure times which depended more strongly on the location of the carbon plies. Carbon plies used as external cladding greatly increased the failure time, and the variability in failure time, in acid at low strain levels, but did not completely inhibit failure. This supports the view that microcracks develop in the outer carbon plies. Failure modes are discussed.