CRACK BRIDGING IN FIBER-REINFORCED CEMENTITIOUS COMPOSITES WITH SLIP-HARDENING INTERFACES

A new crack bridging model accounting for slip-hardening interfacial s hear stress is derived for randomly oriented discontinuous flexible fi bers in cement-based composites, based on a micromechanics analysis of single fiber pull-out. The complete composite bridging stress versus crack opening curve (sigma(B)-delta relation) and associated fracture energy are theoretically determined. A micromechanics-based criterion which governs the existence of post-debonding rising branch of the sig ma(B)-delta curve is obtained. Implications of the present model on va rious composite properties, including uniaxial tensile strength, flexu ral strength, ductility and critical fiber volume fraction for strain- hardening, are discussed together with an example of a 2% polyethylene fiber reinforced cement composite. It is found that the present model can very well describe the slip-hardening behavior during fiber pull- out which originates from fiber surface abrasion at fiber/matrix inter face. In addition, the new model predicts accurately the enhanced toug hness in terms of both ultimate tensile strain and fracture energy of the composite and resolves the deficiency of constant interface shear stress model in predicting the crack opening and ultimate strain, whic h are critical for material design of pseudo strain hardening engineer ed cementitious composites (ECCs). (C) 1997 Elsevier Science Ltd.