<title>Elementary damping properties in braided composite materials</title>

Abstract

This paper investigates the damping level trends of three-dimensionally braided composites as a function of matrix material, fiber-matrix interface, fiber braid angle, fiber volume, and axial fiber tow size. With knowledge of such trends, designers may increase the structural damping in a 3-D braided composite component, thereby reducing component vibration, shock response, and fatigue. The logarithmic decrements of the fundamental mode response of cantilevered, 3-D braided composite beam specimens were calculated for comparison. Although the logarithmic decrements of two specimens, differing only in their matrix materials (Tactix 123 and Epon 828), were essentially identical, both were considerably larger than that for steel. The value for the decrement of these two composite specimens' response was taken as a reference. Altering the nature of the fiber-matrix interface by lubricating the fibers before specimen consolidation greatly increased the damping relative to the baseline. Trends of increasing damping were measured with both increasing fiber braid angle and fiber volume. Finally, increasing levels of damping are reported for decreases in axial fiber tow size. Explanations for these trends, based on the possible microscopic and macroscopic nature of the braided composites, are offered.