Final Evaluation of Rain Erosion Sled Test Results at Mach 3.7 to 5.0 for Slip-Cast Fused Silica Radome Structures

摘要

This report contains a summary of rain erosion results obtained for high-purity slip-cast fused silica (SCFS) models on sleds at Holloman Air Force Base, New Mexico. This effort, which was initiated to evaluate the rain erosion behavior of SCFS as a function of velocity and angle of incidence was completed with good correlation of results. The test were performed in artificial rain at average velocities between 1270 and 1740 m/sec (Mach 3.7 and 5.0). Right circular cone models having semivertex angles of 15, 19, 22.5, 25, 27.5, and 30 degrees were tested. A special test vehicle and sample design were utilized to avoid sled vibration-induced failures that are common to small samples of brittle ceramics at velocities near Mach 5. A unique feature of the sled test vehicle is its capability of testing seven cone frusta, thereby simulating actual radome forebody shapes. The sample design and special mounting technique resulted in obtaining correlatable erosion data which were free of spurious mass losses caused by sample fracture and edge effects. Because SCFS has low fracture toughness and relatively poor rain erosion resistance under severe conditions, other candidate ceramic and plastic radome materials were tested concurrently in the interest of finding a tougher structure. However only those results for SCFS are presented in this report.