Dynamic response of carbon/epoxy composites

Experimental methods for dynamic characterization of composite materials were described. Tensile properties of thin laminates at strain rates up to 500 s^-1 have been obtained by a method employing thin rings under dynamic internal pressure. Unidirectional specimens of carbon/epoxy were used in the form of rings 10.16 cm (4 in.) in diameter, 2.54 cm (1 in.) wide and 6 to 8 plies thick. Internal pressure was applied explosively through a liquid in a specially designed fixture and the transient pressure and strains were recorded. A modified fixture was used for testing thin rings under dynamic external pressure to obtain compressive properties at high strain rates. In the case of thick composites a different method employing falling weight impact was used. A tower with a capacity of dropping a mass of up to 40 kg from a height of up to 3.0 m (10 ft) was constructed and utilized to test composite specimens up to 72 plies thick. The acceleration of the impactor and the specimen strains were recorded. Results obtained to date indicate that, generally, moduli and strengths increase with strain rate. The increase is lowest, below 30%, in the longitudinal direction or for fiber-dominated properties, and highest in the transverse direction and for other matrix-dominated properties. In many cases, including longitudinal, transverse and in-plane shear properties, the ultimate strain does not vary significantly with strain rate.