Mechanical Properties of High Strength, High Modulus to Density Continuous Alumina Filaments for Use as a Reinforcement in Structural Composites.
Abstract
Sapphire filaments twelve inches in length and 3 to 40 mils in diameter have been grown from the melt. The filaments were grown at speeds to 6 inches per minute. Studies of the grown filaments as a function of melt temperature and pulling speed revealed three mechanisms of growth: planar, cellular, and dendritic. These types of growth occurred in the order given as the growth speed and supercooling increased. Studies of the strength and fracture of long single crystal sapphire filaments and ribbons have been conducted. The mean strength of crystals 4 to 7 mils in diameter has been shown to be at least 371 kpsi, with an estimated standard deviation of 67 kpsi. The substructure of the crystals contains subboundaries and other line imperfections, as well as volume imperfections. Comparison of the measured strengths with the theoretical stresses for crack extension by dislocation mechanisms suggests that large weak filaments fail by propagation of pre-existing cracks, while thin strong filaments fail by extension of flaws to the size necessary for propagation. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 1968
- Accession Number
- AD0845110
Entities
People
- A. I. Mlavsky
- George F. Hurley
- Harold E. Labelle Jr.