DEVELOPMENT OF ACCEPTANCE CRITERIA IN CARBON-CARBON MATERIALS FOR SPACE STRUCTURES

CARBON-CARBON (C-C) COMPOSITES ARE AN ATTRACTIVE CLASS OF MATERIALS FOR SPACE SYSTEM COMPONENTS. THEY POSSES HIGH STIFFNESS AND STRENGTH TO DENSITY RATIOS, HIGH THERMAL CONDUCTIVITY, NEAR ZERO THERMAL EXPANSIONS, AND EXCELLENT THERMAL SHOCK RESISTANCE. THESE MATERIALS, HOWEVER, DUE TO THE NATURE OF THEIR FABRICATION AND PROCESSING, INEVITABLY CONTAIN DEFECTS. THE DEFECTS CONSIST OF BROKEN AND MISALIGNED FIBERS, MATRIX CRACKS, AND OTHER INHOMOGENEITIES AND DISCONTINUITIES SUCH AS EXTREMELY POROUS REGIONS AND LARGE REGIONS OF POORLY BONDED FIBERS RESULTING FROM POOR IMPREGNATION AND CARBONIZATION. TO DATE, THERE IS LITTLE UNDERSTANDING OF THE EFFECTS OF THESE FLAWS ON THE MECHANICAL STRENGTH AND STIFFNESS PROPERTIES, OR ON THE THERMAL PROPERTIES OF THE C-C MATERIALS. THE DEVELOPMENT OF IMPERFECTION ACCEPTANCE CRITERIA FOR C-C MATERIALS IS OF PRIME IMPORTANCE TO THE SUCCESSFUL UTILIZATION OF THESE MATERIALS IN SPACE STRUCTURES. CARBON-CARBON MATERIALS ARE EXPENSIVE; WITHOUT ANALYSIS FOR THE CORRELATION OF MATERIAL FLAWS WITH MATERIAL PERFORMANCE, A COMPREHENSIVE EXPERIMENTAL PROGRAM TO DEVELOP ACCEPTANCE CRITERIA IS PROHIBITIVE. THE FOUNDATION FOR ACCEPTANCE CRITERIA DEVELOPMENT, THEREFORE, MUST INCLUDE THE GENERATION OF MATERIAL MODELS WHICH WILL ALLOW FOR THE EVALUATION OF THE EFFECTS OF VARIOUS TYPES AND SIZES OF IMPERFECTIONS ON THE THERMOMECHANICAL PROPERTIES AND STRENGTHS OF C-C COMPOSITES. THE FEASIBILITY OF GENERATING SUCH MODELS IS THE GOAL OF THE PHASE I PROGRAM.