DYNAMIC COMPRESSIVE BEHAVIOR OF THICK COMPOSITE-MATERIALS

The effect of strain rate on the compressive behavior of thick carbon/ epoxy composite materials was investigated. Falling weight impact and split Hopkinson pressure bar systems were developed for dynamic charac terization of composite materials in compression at strain rates up to 2000 s(-1) Strain rates below 10 s(-1) were generated using a servohy draulic testing machine. Strain rates between 10 s(-1) and 500 s(-1) w ere generated using the drop tower apparatus. Strain rates above 500 s (-1) were generated using the split Hopkinson pressure bar. Unidirecti onal carbon/epoxy laminates (IM6G/3501-6) loaded in the longitudinal a nd transverse directions, and [(0(8)/90(8))(2)/(0) over bar(8)](s) cro ss-ply laminates were characterized. The 90-deg properties, which are governed by the matrix, show an increase in modulus and strength over the static values but no significant change in ultimate strain. The 0- deg and cross-ply laminates show higher strength and ultimate strain v alues as the strain rate increases, whereas the modulus increases only slightly over the static value. The increase in strength and ultimate strain observed may be related to the shear behavior of the composite and the change in failure modes. In all cases, the dynamic stress-str ain curves stiffen as the strain rate increases. The stiffening is low est in the longitudinal direction and highest in the transverse direct ion.