In resin injection pultrusion, the liquid resin is injected through the injection slots into the fiber reinforcement; the liquid resin penetrates through the fibers as well as pushes the fibers towards the centerplane causing fiber compaction. The compacted fibers are more difficult to penetrate, thus higher resin injection pressure becomes necessary to achieve complete reinforcement wetout. Lower injection pressures below a certain range (depending upon the fiber volume fraction and resin viscosity) cannot effectively penetrate through the fiber bed and thus cannot achieve complete wetout. Also, if the degree of compaction is very high the fibers might become essentially impenetrable. The more viscous the resin is, the harder it is to penetrate through the fibers and vice versa. The effect of resin viscosity on complete wetout achievement with reference to fiber-reinforcement compaction is presented in this study.

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In the resin injection pultrusion process (RIP), the liquid resin is injected into the continuously pulled fibers through the injection slots to cause complete wetout of the fibers. As the resin penetrates through the fibers, the resin also pushes the fibers away from the wall causing compaction of the fiber reinforcements. When the fibers are squeezed together due to compaction, the resin penetration becomes more difficult; thus a resin injection pressure below a certain pressure cannot effectively penetrate through the fibers and achieve complete wetout. However, if the resin injection pressure is too high, the fibers are squeezed together to such an extent that the fiber becomes essentially impenetrable by the liquid resin. The harder it is to penetrate through the fibers, greater is the tendency of the fibers to be pushed away from the wall and cause compaction and affect wetout. In this study, the effect of fiber volume fraction on the fiber reinforcement compaction and the complete wetout is presented.

Nomenclature a o = freestream speed of sound, m∕s c p = specific heat at constant pressure, kJ∕kg · K g c = Newton's constant, kg · m∕N · s 2 h pr = fuel lower heating value, kJ∕kg M c = combustion Mach number M o = Mach number at freestream conditions M o

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