Chapter 16. Reinforcing Fused Silica with High Purity Fibers

Summary

Ceramic composites consisting of high-purity fused silica fibers dispersed in a high-purify fused silica matrix were successfully fabricated containing up to 10 vol% fibers. Short chopped fibers were employed and were randomly oriented in the matrix. Composite densities varied from 1.88 to 1.97 g/cc. Variations in Young's modulus were experienced because fibers were not evenly distributed throughout the matrix material. Single Edge Notch Beam tests indicated no effect of the fiber additions upon K_IC. Work-of-fracture, as determined by triangular notched-beam tests, showed a dramatic increase due to the fiber additions, particularly for 2.5 and 75 vol%. Maximum break loads (SENB) were similar for fiber-reinforced vs monolithic fused silica, but the work required to push a controlled crack (WOF) through a specimen was appreciably greater for the reinforced material. Indeed, In some instances in the SENB tests for the fiber reinforced specimens after maximum load was achieved, the crack did not always propagate entirely through the specimen. Rocket-sled rain erosion testing of the fiber-reinforced fused silica materials indicated approximately a ten percent reduction in the mass-loss ratio, calculated as the ratio of mass loss in the specimen to the mass of rain encountered In the rainfield. Composite samples experienced rather severe erosion, but they did not crack catastrophically as did some unreinforced fused silica samples under Identical test conditions. The erosion of the composite samples was more uniform around the sample surface than that for monolithic fused silica. These results tend to support the fracture toughness results.