Massachusetts Institute of Technology, Cambridge, MA
Advanced Research Laboratory, IJBU, Hewlett-Packard Company, Corvallis, OR
(Received 18 April 1996; accepted 1 November 1996)
Crack propagation in fiber reinforced composites is governed by bridging stresses provided by fibers along the crack. To predict the behavior of fiber reinforced structural components under general loading conditions (where mixed mode crack propagation is possible), the normal and shear stresses acting on a crack need to be obtained as a function of crack opening and shearing displacements. In this investigation, a mixed mode fiber pull-out equipment is developed to measure both the normal and shearing bridging forces as a fiber is being pulled and sheared. With slight modifications, the setup can also be employed to study the effect of lateral stresses on fiber pull-out. To demonstrate the applicability of the novel equipment, pull-out tests were carried out with steel fiber reinforced mortar specimens. Experimental results indicate: 1) high sensitivity of fiber pull-out behavior to lateral stresses; 2) dependence of both normal and shear bridging forces on crack opening as well as shearing displacements; and 3) dependence of crack bridging forces on crack opening/shearing displacement history. These experimental observations provide new insights and challenges to the micromechanical modeling of fiber composites.
Paper ID: JTE11340J