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In this study, the impact strength multi-layer slabs reinforced by steel and nylon fibers, as well as the combination of these two fibers under the influence high velocity projectile, was investigated. To achieve this goal, 30 slabs one layer and three layers with dimensions 40 *40 * 7.5 cm were reinforced by 1% of the fiber, 30 slabs made 10 different models , each with 3 models Sample was made. A non-fiber model, as a control sample, and other slabs all have a constant volume 1 percent fiber, the difference being in the type and composition the fibers in different layers the slabs. The slabs were made with Kalashnikov , PK Kalashnikov and Dragunov guns at a distance 50 meters tested. In the test the projectile's encounter, three parameters penetration depth, area the damaged front and rear area and the volume damaged area in the samples were calculated and compared. Based on the results obtained, steel fibers can increase the resistance concrete slabs against the impact the projectile and reduce the surface area and volume the damaged area and significantly reduce the penetration depth. Steel fibers at best reduced the penetration depth 64 % in the kalashinkov gun and reduced the area and volume the damaged area in the dragunov weapon by 88 % and 98 % respectively. Also, steel fibers can prevent crack expansion by increasing the bond strength, provided that the fibers the nylon have a much lower impact than steel fibers. the nylon fiber could reduce the penetration depth and demolition area the sample in kalashnikov weapon by 37 % and 59 %, respectively, and reduce the volume damaged area in the dragunov weapon by 84 %, respectively. In addition, in this research, 12 samples cubic pressure were placed on the side 10 cm, 12 cylindrical tensile samples 10 × 20 cm and 12 small flexion beams with dimensions 32 *8 *6 cm and tested. It was observed that steel and nylon fibers cannot have a significant effect on the compressive strength, As a result the addition one percent the steel fiber, nylon and a combination these, this increase is 7.7, 2.6 and 6.4 % , which can be neglected. but steel fibers can significantly increase the tensile and flexural strength the concrete. addition one percent the steel fiber could create a 2.5 – fold increase in tensile strengths and increase the resistance 2 - fold in bending specimens. This is the nylon fibers do not have a significant impact on the tensile and flexural strength. Adding one percent the nylon fibers in the tensile and flexural samples could increase the resistance these specimens by 16 % and 24 % respectively. It was observed in the bending test of beams that steel and nylon fibers can be bent by bending in the cracks to increase the shape the weld so that the change in the maximum area the beam with the addition one percent steel fiber from about 4 mm in the control sample increase to about 25 mm.

Keywords: impact resistance, multilayer slabs, steel fibers, nylon fibers, projectile impact

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