Compressive deformation of embedded high-performance polymeric fibers

Abstract

A composite sample fabrication technique was designed and demonstrated for applying direct axial compression to high-performance polymeric fibers for studies of fiber microstructure under in situ compression. Two kinds of polymers were involved in the fibers of interest. One is a polymer of rigid-rod molecule; the other is a polymer of extended coil-like molecule. A multifilament fiber bundle was aligned uniaxially and embedded in an epoxy matrix. The composite sample geometry and the Poisson's ratios were analyzed by finite-element computations that suggest that a high modulus matrix is required for inducing high-compressive load and large stress gradient along the embedded fiber. This was verified by optical microscopy on compressed composite samples and facilitated the selection of the epoxy matrix. A compressive strain of 2% was successfully applied to the polymeric fibers resulting in the fiber kink band formations, which are considered a fiber compressive failure, for microstructure studies. Our sample fabrication also indicates that fibers of rod-like polymer have a lower critical compressive strain compared to that of fibers of coil-like polymer. X-ray scattering results are also introduced to show the validity of the prescribed technique for examining the microstructure of fibers under compressive deformation.