Fatigue Performance of Thermoplastic TuFF Composites

Tailorable universal Feedstock for Forming (TuFF) is a composite material consisting of highly aligned short fibers able to achieve high fiber volume fraction (up to 60%). The high degree of alignment, high fiber volume fraction (FVF) and high level of fiber-matrix adhesion provides quasi-static mechanical properties comparable to continuous fiber composites using a fiber aspect ratio of 600. However, in structural applications, it is important to consider the fatigue behavior of TuFF, particularly because the complex load transfer paths among the discontinuous aligned fibers may affect the properties. In this work fatigue performance of unidirectional carbon fiber/polyetherimide TuFF composites (3mm IM7, 57% FVF) are tested in tension (R = 0.1) to generate the S-N curve. Digital Image Correlation (DIC) is used to measure effects of cyclic loading on modulus. Failure surfaces are examined using microscopy to determine failure modes. It is demonstrated that TuFF material has comparable fatigue performance to other continuous carbon fiber structural composite materials reported in literature.