Abstract
Mechanical properties of three-dimensional carbon fabric/PMR polyimide composites were investigated in an effort to delineate the role of reinforcing fabric structure on the performance and durability of an ultra high performance 3D composite. There were four fabric structures evaluated: three-dimensional three-axial (3D-3A) and three-dimensional five-axial (3D-5A), both having 5.0 and 7.5 mm weave gauge. Composites made from these four fabric preforms and polyimide matrix resin were fabricated and tested under identical conditions. The mechanical properties were measured, including strength, modulus and work of rupture in tension and flexure at 25, 200, 300, 370 and 450°C. Our results showed that the 3D-3 A composites had higher tensile and flexural properties than their 3D-5A counterparts, with one exception: the 3D-5A materials showed better flexural work of rupture. The 3D-3A composites exhibited higher retention of mechanical properties at elevated temperatures, compared to the 3D-5A composite materials, indicating that the 3D-3A materials had better thermal oxidative stability. Most of the composites retained over 50% of their mechanical properties after 24 hours exposures at 370°C.