Date of Award

12-1-1991

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Aeronautics and Astronautics

First Advisor

Shankar Mall, PhD

Abstract

An investigation was conducted to study the thermomechanical fatigue (TMF) response of a [±45]2s angle ply SCS-6/titanium-15-3 metal matrix composite (MMC). Load controlled in-phase TMF experiments were performed over the temperature range 149-427 C, with a cycle frequency of 0.02 Hz. Test equipment included a high temperature extensometer, quartz lamp radiative heaters controlled by a Micricon thermal control unit and TMF test control software, MATE263. Stress and strain hysteresis, total strain and stiffness were monitored to characterize material behavior. Large plastic deformations were observed in all specimens, with total failure strains ranging from 7 to 13 percent. It was observed that the total strain to failure was proportional to the maximum applied cycle stress. Damage mechanisms, studied using edge replication and optical and scanning electron microscopy, showed transverse microcracks originating at the fiber-matrix interface and slip bands and fiber sliding in the matrix. Three phases during fatigue life were observed in the tested specimens: (1) interface damage; (2) matrix hardening; and (3) matrix damage. Cold working of the matrix was a probable factor in the matrix hardening. The fibers did not affect the fatigue behavior which was dominated by matrix response.

AFIT Designator

AFIT-GAE-ENY-91D-21

DTIC Accession Number

ADA243871

Comments

The author's Vita page is omitted.

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