DAMAGE-BASED MODELING OF FIBER PULLOUT UNDER VARIABLE COMPRESSIVE STRESS

When steel fibers are pulled out from a cementitious matrix, the inter facial friction decreases with sliding distance. The frictional decay is a function of the far-held lateral stress. In this paper, a damage model is developed to derive the interfacial friction in terms of the sliding distance as well as the lateral compression history. The model assumes the interfacial friction to be governed by two related parame ters: the interfacial residual stress tau(iO) (reflecting the fiber/ma trix misfit) and the interfacial friction coefficient <(mu)over bar> ( reflecting the surface asperity). This work shows experimentally that fur a given interface, a unique relationship, independent of sliding d istance and lateral compression history, exists between tau(iO) and <( mu)over bar>. Based on this observation, a damage model, which evaluat es the interfacial residual stress tau(iO), only, is developed to pred ict the pullout curves under variable lateral compressive stress. An a pproach to account far material variability from one batch of specimen s to another is also proposed. Theoretical prediction of pullout behav ior under various loading histories is found to compare favorably with experimental results.