Effect of fiber nano-scratch on macro strain hardening behavior in engineered cementitious composites

The surface of pulled out fiber from the cementitious matrix reveals some scratches. It can be considered that the fresh cement paste can penetrate into the pores of hydrophilic poly (vinyl alcohol) (PVA) fibers which is converted to some hard teeth in the pores of the fiber after cement hydration. The hard teeth scratch the fiber surface during pull out which introduce energy consuming and slip hardening. In the current study, some nano-scratches with the length of 3 μm and the depths of 50, 150 and 250 nm are produced on two different PVA fibers the required force at different scratching rates are evaluated. The nano-scratches are made by an innovative inverse fly-mode technique in atomic force microscopy. The results indicate that the required force increases as the hardened teeth is further scratching the fiber which causes the strain hardening. However, the fibers showing significant roughness and high resistance against scratch fail during fiber pull out which deteriorates the strain hardening.