Abstract
LARC™-SI (NASA Langley Research Center-Soluble Imide) is an aromatic thermoplastic polyimide. LARC™-SI is synthesized from equimolar amounts of oxydiphthalic anhydride (ODPA), 3, 3′, 4, 4′-biphenyltetracarboxylic dianhydride (BPDA) and the equivalent amount of 3, 4′-oxydianiline (3, 4′-ODA). Phthalic anhydride (PA) was used as an endcapper to control molecular weight. A 30% solid LARC™-SI solution (in NMP/Xylene: 9/1 v/v) with 3% stoichiometric imbalance was made into unidirectional long-fibre-reinforced prepregs. Thermal properties, volatile depletion behaviour and resin rheology were thoroughly characterized. Using this information, two composite moulding cycles were developed that consistently yielded well consolidated, void-free laminates. Composite mechanical properties such as short-beam shear strength, longitudinal and transverse flexural strength and flexural modulus, longitudinal tensile strength and notched and un-notched compression strengths, fracture toughness, open-hole compression strength and compression after impact (CAI) strength were measured at room temperature (RT) and elevated temperatures. LARC™-SI composite exhibited very good toughness and damage tolerance. The interlaminar fracture toughness and the CAI strength were measured at 1.72 kJ m−2 at 35.2 GPa respectively.
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