Composite Interfaces, Vol. 7, No. 4, pp. 257– 275 (2000)  VSP 2000. Discontinuous surface-treated submicron-diameter carbon filaments as an interlaminar filler in carbon fiber polymer-matrix composites for vibration reduction MARTIN SEGIET and D. D. L. CHUNG Composite Materials Research Laboratory, State University of New York at Buffalo, Buffalo, NY 14260-4400, USA Received 10 July 1999; accepted 13 May 1999 Abstract—Discontinuous surface-treated submicron-diameter carbon filaments are effective for use as an interlayer between continuous carbon fiber laminae in a nylon-6 matrix composite for enhancing the loss tangent (0.2 and 1.0 Hz) under flexure that involves bending of the fibers, without significant decrease of the flexural storage modulus or the tensile modulus or strength in the fiber direction. The surface treatment is oxidation using ozone. Without treatment, the filaments are not effective. The treated filaments amount to 0.64 vol.% of composite; the interlayer thickness is 77 μm. A viscoelastic interlayer is even more effective than the treated filament interlayer for enhancing the loss tangent, but the accompanying decrease in storage modulus is much more. The loss tangent for composite with viscoelastic interlayer decreases upon heating, so the loss modulus for this composite is less than that of the composite with treated filament interlayer at  50 ◦ C. Keywords: Polymer–matrix composite; damping; vibration; mechanical; carbon fiber; nylon. 1. INTRODUCTION Structural vibration control is important for essentially any structure, whether bridges, aerospace structures, turbine blades or skis. Due to the increasingly common use of one-piece composite constructions, vibration damping derived from fastened joints is insufficient and that derived from the composite material itself is needed. A conventional way to increase the damping capacity of a structure is the attaching or embedding of a viscoelastic material on or in the structure [1– 7]. For example, in the case of a continuous fiber polymer– matrix composite, which is the most common form of structural composite, a viscoelastic sheet can be placed as an interlayer in the interlaminar region between the continuous fiber layers during