Analysis of steel fibre pull-out from a cement matrix using video photography

Video photography of specially prepared specimens allowed identification of the operative energy dissipation mechanisms during pull-out of straight and bent steel fibres from a cement matrix. Correlation between the observed pull-out process and the significant features of the load-displacement curve was established. Both the straight and the bent fibres exhibited fibre/matrix debonding and frictional sliding, while only the bent fibres experienced plastic deformation as an additional energy dissipation mechanism. Qualitative mechanics models explained the dependence of the maximum pull-out and plateau loads as a function of plastic deformation and frictional sliding. Experimentally obtained maximum and plateau loads plotted as a function of fibre diameter squared yielded straight lines that passed through the origin and increased in slope with increasing bend angle.