Pullout resistance of crimped reinforcing fibers using cold-drawn NiTi SMA wires

Abstract

This paper assesses the bond strength of crimped fibers manufactured by a cold-drawn SMA wire using a continuous method. Several pullout tests are conducted to study bond strength and crack-closing ability of crimped SMA wire. Before and after SMA heating, the pullout force–displacement relationships of crimped fibers are compared with different types of end-shapes, namely, straight and paddled end, to measure the bond strength of these fibers in cementitious composite material. The cold drawn fiber with more than 4% area reduction ratio due to cold drawing work should be used for producing crimped fibers to overcome the stretching effect of indentation by heating. The paddled fibers show almost twice energy dissipation capacity than the crimped fibers, while secant stiffnesses of the crimped fibers are larger by 20% on the maximum than those of the paddled fibers. Crack-closing ability of crimped fibers may be evaluated when the stretching effect at the bent parts due to thermal expansion are compared with recovery effect of prestrain due to shape memory effect. The experimental data reveals the efficiency and applicability of the crimped SMA fibers in contrast to other end-shape SMA fibers provided by discontinuous methods.