Cement composites subjected to high-velocity projectile shows local failure and it can be suppressed by improvement of flexural toughness with reinforcement of fiber. Therefore, researches on impact resistance performance of cement composites are in progress and a number of types of fiber reinforcement are being developed. Since bonding properties of fiber with matrix, specific surface area and numbers of fiber are different by fiber reinforcement type, mechanical properties of fiber reinforced cement composites and improvement of impact resistance performance need to be considered. In this study, improvement of flexural toughness and failure reduction effect by impact of high-velocity projectile have been evaluated according to fiber type by mixing steel fiber, polyamide, nylon and polyethylene which are have different shape and mechanical properties. As results, flexural toughness was improved by redistribution of stress and crack prevention with bridge effect of reinforced fibers, and scabbing by high-velocity impact was suppressed. Since it is possible to decrease scabbing limit thickness from impact energy, thickness can be thinner when it is applied to protection. Scabbing of steel fiber reinforced cement composites was occurred and it was observed that desquamation of partial fragment was suppressed by adhesion between fiber and matrix. Scabbing by high-velocity impact of synthetic fiber reinforced cement composites was decreased by microcrack, impact wave neutralization and energy dispersion with a large number of fibers.
The aim of this study is to evaluate the fracture characteristics of ductile fiber reinforced cement based composites with 1.5 volume ratio of polyvinyl alcohol and steel fiber by high velocity impact of steel projectile. We used gunpowder impact facility to evaluate the fracture characteristics of ductile fiber reinforced cement based composites by collision of steel projectile, and the impact velocity was from about 150 to 1,000m/s. The results of evaluation on the fracture characteristics of ductile fiber reinforced cement based composites were penetration grade, which is the kinetic energy more than three times of no-fiber reinforced specimen (Plain). In addition, ductile fiber reinforced cement based composites did not occurred critical damage other than the debris. In the case of mass loss, Plain specimen was proportional to kinetic energy of steel projectile, while ductile fiber reinforced cement based composites was not significantly affected by kinetic energy of steel projectile. In particular, this tendency had a close relationship with the fracture characteristics of back side of specimens, and the scabbing inhibiting efficiency of PVA specimen was higher than S specimen. In the results of verifying relationship between front and back side calculated by local damage, scabbing occurred at the region close to the back side in the ductile fiber reinforced cement based composites unlike Plain specimen. Thus, in this study, we examined principal fracture behaviors of ductile fiber reinforced cement based composites under collision of steel projectile, and verified that impact resistance performance was improved as compared to Plain specimen.
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