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The influence of materials construction variables and environmental parameter effects on the rain erosion behavior of carbon-carbon reentry vehicle nosetip thermal protection materials has been investigated at velocities of 1220 to 1675 m/s by firing rocket sleds equipped with special specimen holders through the artificial rain-field at Holloman Air Force Base.
A high percentage of axial reinforcement (fibers end-on to the surface) is desirable in carbon-carbon composites for improved erosion resistance. One-dimensional reinforcement of this type would provide maximum erosion resistance, but the need for structural properties in reentry vehicle applications requires a combination of this high axial loading with fine-weave orthogonal 3-dimensionally reinforced construction for enhanced erosion-resistance and balanced performance. The small unit cell size is essential for good resistance. Increased in-plane isotropy in these composites by rotating the X-Y plies reduced the macroroughness development which is typical of the carbon-carbon composites in the multiple rain environment.
Improvements in weaving, impregnation, pyrolysis, and graphitization are reflected in a reduction in the mass loss ratio of composites which have similar Z bundle area fractions, but were made at different chronological times.
It was determined that Thornel 50 fiber composites gave better performance than Thornel 75, C-1000, C-3000, and other fibers. The introduction of intermediate chemical vapor deposition (CVD) of carbon coupled with low- or high-pressure pitch processing provided matrices for composites with improved erosion resistance compared with pyrolyzed resin or pitch-only processes.
Empirical relationships were determined to govern the erosion rate as a function of velocity and impingement angle.
rain erosion, carbon-carbon composites, rocket sled testing, multiple impact, materials construction variables, supersonic velocity, erosion
Materials research engineer, Air Force Materials Laboratory, Wright-Patterson Air Force Base, Ohio