Damage Accumulation in Graphite-Epoxy Composites During Compressive Fatigue

There has recently been considerable interest in the behavior of thick section (one inch and greater) polymer composites under compressive loads [1]. Strength, fatigue life and damage modes are characteristics which design and inspection engineers seek to understand to properly utilize these materials in applications where compressive loads are encountered. This paper presents a brief summary of some of the progress in a research effort to characterize the compression-compression fatigue behavior of thick section fiber reinforced polymer composites. Primary objectives of this research are to determine fatigue life and strength, and to use nondestructive techniques to predict material failure with particular interest in identifying the early stages of damage. Destructive techniques are implemented to correlate actual damage mechanisms to any “fingerprint” found by NDE methods. Specifically, one inch thick, double edge notched, graphite epoxy coupons were fatigued to failure while structural stiffness and acoustic emissions were monitored. Unfailed specimens were examined using ultrasonic C-scan and X-ray radiography after which they were cut and polished for damage identification via microscopy.