Date of Award

12-1991

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Aeronautics and Astronautics

First Advisor

Shankar Mall, PhD

Abstract

Off-axis loading of eight ply, unidirectional specimens with and without a circular hole determined the ultimate tensile strength of SCS-6/Ti- 24A1-11Nb composite at temperatures of 25°C and 650°C and fiber orientations of 0 degrees, 15 degrees, 45 degrees. Longitudinal moduli of the tested orientations compared closely to the rule of mixtures calculated values, and strengths compared closely to those predicted by the Tsai-Wu failure theory. The small diameter hole does not act as a stress concentrator, but merely reduces the material's strength in proportion to area loss. This result differs from those predicted by linear finite element analysis and orthotropic stress concentration theory. Radiography, used to detect damage prior to failure, showed no fiber breakage nor matrix cracking. Microscopic examination of the fracture surfaces indicates a weak fiber/matrix interface bond at both room and elevated temperatures. Brittle fracture of fibers and matrix with little fiber pull out occurs at room temperature, while brittle fiber fracture and ductile matrix fracture with greater fiber pull out occurs at elevated temperatures.

AFIT Designator

AFIT-GAE-ENY-91D-8

DTIC Accession Number

ADA243869

Comments

The author's Vita page is omitted.

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