Dynamic fibre push-out test applied to metal-matrix composites

The dynamic fiber/matrix interface strength for a silicon-carbide-fiber-reinforced, titanium-alloy metal-matrix composite was measured by impacting the end of a fiber extending through a thin specimen with a diamond-tipped projectile at ~2 m/s. The matrix surrounding the distal end of the fiber was supported on the end of a Hopkinson bar fabricated from hypodermic needle tubing, and an interferometer was used to measure the axial velocity of the tube, from which was obtained the force. The dynamic push-out force measured in these experiments is about one-third the static push-out force measured by others on specimens of the same material at similar thickness. 1 . INTRODUCTION In fiber-reinforced composites, load is transferred between the fibers and matrix by shear forces acting on the sides of the fibers. When there is a crack in the matrix, these shear forces enable fibers that bridge the crack to limit crack opening. These forces also cause fiber failure. Thus, the shear properties of the fiber/matrix interface are key to understanding cracking in composites, whether at quasistatic or dynamic loading rates. Dynamic rates can arise in impact loading or in cases where a quasistatically loaded crack propagates rapidly. The connection between interface shear and composite fracture has been established by analyses [1-4] which show that variations in slip hardening behavior influence crack opening behavior. Force as a function of slip has been measured quasistatically using push-in [5], push-out [6], and pull-out [3] techniques. Analyses of these techniques that have appeared in the literature [3,5-8] suggest that there are two phases in the push-out process: debonding and sliding. The analyses also suggest that characteristics of both phases can be obtained from measurements of the push-out force and fiber/matrix relative displacement. To our knowledge, no push-out measurements have been made at sliding rates higher than 0.002 m/s in metal-matrix composites (MMCs). Our objective has been to measure the force-versus-sliding Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jp4:1994806 JOURNAL DE PHYSIQUE IV relation for silicon-carbide-fiber-reinforced, titanium-alloy matrix (Sic n i 15 3) composite at high sliding rates. Our approach has been to develop an experiment wherein the e n d o f i fiber is impacted with a projectile and the push-out force is deduced from the reaction force of the matrix against a tubular Hopkinson bar.