Alvin N. Ruiz

Date of Award


Document Type


Degree Name

Master of Science


Department of Aeronautics and Astronautics

First Advisor

Shankar Mall, PhD


The objective of this study was to investigate the residual strength of a cross-ply, SCS-6/Ti-15-3, metal matrix composite (MMC) at elevated temperature (427 °C) when exposed to fatigue loading. Several specimens were subjected to a strain-controlled, fully reversed loading (R=-1), at various strain levels. The specimens were fatigued up to a portion of their life expectancy and then loaded to failure. Stress and strain data obtained during the test provided useful information for the macro-mechanical behavior of the material. It was determined that the residual strength was directly related to the amount of damage present in the matrix, meanwhile, the amount of matrix damage was dependent on the number of cycles and strain level the specimen had been exposed to. It was also observed that the residual strength under the strain controlled mode degraded more consistently than its counterpart under load controlled mode. This variation, however, may be due to the frequency and R-ratio differences between the two loading modes. The comparison of the residual strength degradation of the cross-ply vs. unidirectional laminates reflected a significant difference due to ply orientation. The unidirectional composite exhibited much less residual strength degradation due to the absence of the crack initiation action attributed to the 90° plies in the cross-ply.

AFIT Designator


DTIC Accession Number