Hygrothermal Influence on the Flexural Properties of Kevlar-Graphite/Epoxy Hybrid Composites

ABSTRACT: The hygrothermal influence on the flexural properties of unidirectional Kevlar 49-graphite/epoxy hybrid composite was investigated in the temperature range-50°C to 150°C. Moisture was introduced into the specimen by immersion in distilled water. Two material lay-ups were used in this investigation. In Kev 49/T-300/Kev 49, Kevlar 49 and graphite prepreg are used as outer and center layer, respectively and in T-300/Kev 49/T-300, it was vice-versa. In both cases the tapes were alternated until the total thickness was achieved. Data for the determination of flexural strength and modulus were generated at various temperatures for both dry and saturated specimens. The results show that both flexural strength and modulus change with the ply sequence of hybrid lami-nates. The flexural strength and modulus of Kev 49/T-300/Kev 49 are relatively higher than those of T-300/Kev 49/T-300. The apparent flexural strength decrease with the in-crease of temperature in the range 23°C to 150°C. The addition of moisture further degrades the flexural strength in the same temperature range. At low temperature (-50°C) the addition of moisture resulted in an increase in the flexural strength of Kev 49/T-300/Kev 49. Both tensile and compressive failures take place in flexural test and the failure mode changes with the aging condition