Date of Award

12-1990

Document Type

Thesis

Degree Name

Master of Science in Aeronautical Engineering

Department

Department of Aeronautics and Astronautics

First Advisor

Shankar Mall, PhD

Abstract

This study investigated the fatigue damage initiation and progression in SCS-6/Ti-15-3 under an environment of fatigue loading at isothermal temperature. This program included two parts. First, an 808 Ultimate Tensile Strength system was set up to accommodate testing at two frequencies of 2.0 and 0.0208 cps at a constant temperature of 427° C. Second, at intervals during the load cycle process, the test specimens were characterized by establishing damage parameters based on changing modulus of elasticity, average strain, strain range, and ultimate tensile strength. Damage progression was documented in the form of failure of the fiber-matrix interface, matrix cracking, fiber breaking, and debonding of the fibers. Crack initiation locations and growth patterns were peculiar to specific test conditions of frequency and stress level. Also, analysis of the fatigued specimens and test data revealed matrix failure mechanisms ranging from ductile failure to cleavage fracture. The results of this study clearly show that temperature, frequency as well as stress levels are important design considerations for this composite in fatigue loading applications.

AFIT Designator

AFIT-GAE-ENY-90D-20

DTIC Accession Number

ADA230388

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