Acoustic emission analysis and small-angle X-ray scattering from microcracks during deformation of ETFE composites

Abstract

During the deformation of an unfilled matrix of ethylene-tetrafluoroethylene (ETFE), microcracking was observed by small-angle X-ray scattering (SAXS), although it does not cause significant acoustic emission because the released energy is too small to be detected (size of microcracks≪size of fibres). Fibres induce local stress maxima and increase the formation of microcracks. Fibre delamination processes were monitored by acoustic emission analysis. The use of coupling agents improves the fibre-matrix adhesion and increases the mechanical yield stress and decreases delamination processes. A simple model for estimating the energy released by fibre delamination processes was suggested. The predicted difference in peak amplitude between the two extreme processes agrees well with the results of the experiments. The characteristic values of the peak amplitude distributions, however, do not show any significant dependence on fibre coating or testing temperature. Further investigations by SAXS and acoustic emission analysis, especially at low strain, will be necessary to obtain more detailed information about the initial formation of microcracks and fibre delamination.