Compressive and Flexural Creep Behavior of Carbon Fiber/PEEK Composites

Abstract

The present study deals with the compressive and flexural creep properties of polyetheretherketone (PEEK), a high temperature semicrystalline thermoplastic. The compressive and flexural modes are important from a practical viewpoint, and yet rather limited viscoelastic data exist presently for testing in the two modes. The creep compli ance results of the unreinforced PEEK and the carbon fiber/PEEK composites are reported for temperatures ranging from 120°C to 160°C. Transverse compressive and cross-ply [±45°] s flexural compliances, the matrix dominated properties, displayed a significant viscoelastic behavior. The unidirectional 0° samples, on the other hand, displayed only a very limited time dependent response since the composite properties in the longitudinal direction are controlled by the almost elastic response of the fibers. The time-dependent experimental compliance values for the composites are compared to the results predicted from a micromechanics model and the classical lamination theory in conjunction with the quasi-elastic methodology.

Tertiary compression creep of long-fiber composites: A model for fiber kinking and buckling

“…2 n c c [13] calculations, that assume ub c ϭ m (represented by dotted lines in Figure 8), display the same qualitative and virtually For a particular temperature and fiber volume fraction, the the same quantitative functional dependence as the lowerindependent parameters , , and (all in the units of bound calculations, that assume lb…”

“…This increases the creep-rate contribution from the kink band (Eq. [13]) and, thus, results in anisotropy in creep strengths, and, thus, fiber rotations cause a relatively higher increase in creep rates. an increase in the composite creep rate.…”

“…[13] by using (represented by solid lines in Figure 8). three different creep tests on long-fiber composites with The tertiary kink model is applied to a composite with fibers aligned at three different angles to the loading direction an initial kink angle of 2 deg and an initial kink fraction of ␣, i.e., ␣ 1 , ␣ 2 , and ␣ 3 , the details of which are discussed in 1/10.…”

“…[7] While the compressive Very few creep studies exist for polymer matrix composites response of these composites is expected to be qualitatively under compression. [13] similar to their tensile response during the primary and secWe chose the NiAl-W system as a model system to systemondary creep stages, the onset and progression of instabilities atically study the compression-creep behavior of long-fiber in compression are expected to be different from those in composites for the case where both the (NiAl) matrix and tension and could pose serious design limitations for comthe (tungsten) fibers exhibited creep deformation. These posite use at elevated temperatures.…”

“…In the first stage, the Thus, using Eqs. [13], [11], [4], and [2] in Eq. [1], the composite creep rate remains almost constant.…”