Uniaxial fatigue behavior of filament-wound glass-fiber/epoxy composite tubes

Filament-wound polymer-matrix composite tubes find uses as pressure vessels, rocket launchers, etc., where internal pressure is the primary constraint. Increasing use of these structural parts has given rise to the need for tests to identify characteristics of their fatigue behavior. The aim of this study was to determine fatigue data, and observe macroscopic and microscopic damage mechanisms of filament-wound composite tubes under axial cyclic loading. For this purpose, fatigue lives of the epoxy matrix, ±55° glass fiber-wound specimens are determined for stress levels of 60, 70, and 80% of their tensile strength. Three different frequencies; 0.1, 1, and 10 Hz, were applied at each stress level for the constant amplitude sinusoidal loading with a stress ratio of R= 0.1. Results were evaluated in the form of S-N curves to reveal the effects of stress level and loading frequency on the three stages of fatigue damage. These stages observed were; first craze initiation in the matrix, then craze propagation and densification along the fiber winding direction, and finally breakage in the fibers leading to disintegration. Fatigue lives of the specimens decreased with an increase in the stress level, while they were generally increased by increasing the frequency.