Date of Award

12-1992

Document Type

Thesis

Degree Name

Master of Science

Department

Department of Aeronautics and Astronautics

First Advisor

Shankar Mall, PhD

Abstract

A study was conducted which investigated the behavior of a cross-ply [0/90]2S Nicalon/Calcium-Aluminosilicate (Nicalon/CAS) ceramic matrix composite at room temperature under tension-compression fatigue loading. Material behavior and damage was recorded by stress-strain curves, elastic modulus, hysteretic energy density, and acetate replication techniques. Tension-tension fatigue tests at a load ratio R of 0.1 (R = σmin/σmax) were completed which determined that 140 MPa was the maximum stress allowable in which cycle runout (1,000,000 cycles) would occur. Above this value, transverse crack density increased with respect to cycles and failure ultimately occurred. Tension-compression tests were then performed at load ratios of -2.0, -1.5, and -1.0 with 140 MPa as the maximum tensile stress. In all cases, longitudinal cracks parallel to the loading direction developed. The greater the magnitude of the compressive load, the sooner these longitudinal cracks appeared. Failure always occurred in compression due to buckling of individual plies, thus indicating that tension-compression can significantly reduce fatigue life. Using the elastic modulus as a means of verifying damage was acceptable, but it did not reasonably predict specimen failure. on the other hand, the area under the stress-strain curve (hysteretic energy density) was a better indicator of probable failure since specimens which achieved cycle runout showed either a decreasing or constant energy density while those which failed always showed an increasing value.

AFIT Designator

AFIT-GAE-ENY-92D-02

DTIC Accession Number

ADA259209

Comments

The author's Vita page is omitted.

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