The damage tolerance of fire-retardant glass-epoxy laminates

Alumina trihydrate is an effective and widely used fire retardant and smoke suppressant, with several other incidental advantages, but it usually lowers the mechanical strength of thermosetting resins and laminates. This paper reports the extent of the reduction in the impact damage tolerance of glass-epoxy woven roving laminates, when measured by determining their compression strength retention after impact (CAI). Inserting aramid plies reduced rather than increased the damage tolerance at low impact energies, regardless of their position. Tentative reasons for this observation are offered. Other material changes were also investigated. The benefit of using a rubber toughening modifier (Hycar ATBN) in the epoxy matrix was confined to the lowest impact energy range. Changing the epoxy resin curing agent from a cold curing, mixed amine system to a hot curing piperidine one resulted in an improved compression strength before impact, and in some cases also an improvement in post-impact strength retention.