IMPACT EFFECT IN COMPOSITE CONCRETE PANELS

Abstract

Composite materials have a high resistance to short duration, high intensity loads such as caused by impact of projectiles and accidental or deliberate blasts. The energy absorbing capacity of ferrocement is quite high, compared to conventional reinforced concrete. These materials are lighter in weight, thinner but more resistive barriers, cost effective, prefabricated and can be easily transported to the site of construction. The study was based on an experimental investigations carried out, using fibrous Ferro cement specimens. The test variables were the steel fiber content, percentage of reinforcement I mesh and thickness of the specimen. The study includes impact resistance of fibrous-Ferro cement panels against small arms effect. The panels were of the two sizes lmxlm and 0.5 mx0.5 in. The sectional thickness of the panels ranges between 30 mm to 100 mm. The phenomenon noted was the . penetration level of the bullets, diameter of the hole formed by the projectile and the crack pattern around the entry and exit points. The theoretical value of the sectional thickness required for, preventing perforation was also calculated to give an idea of lethality of the projectile. The degree of damage was assessed qualitatively by studying the crack pattern and spalling. Results obtained were: 1. In' first group of panels i.e. when testing carried out on 1000 mmx 1000 mm Panels with 9 mm Machine carbine it was observed that the bullets have pierced through the30 mm thick panel but could not penetrate through 50 mm thick panels. Penetration observed in this case was 15 mm only. With 7.62 mm self loading rifle and 7.62 mm Light machine gun fire from100 m and 50 m distance, it was noticed that all the rounds have pierced through all the panel and no crack formation took place. Minimum 10 mm and maximum 20 mm diameter holes were formed. There was 75 mmx100 mm size spalling seen on rear side of the panel around the hole. There was no crack formation. In case of second group of panels i.e.500 mmx500 mm with 30 mm, 50 mm,75 mm and 100 mm thickness, the results were as follows: When the bullets were fired with 9 mm Machine carbine from 50 m range the bullets have penetrated through 30 mm and 50 mm thick panels but could not penetrate through 75 mm and100 mm thick panels and the depth of penetration observed was 15 mm only. When the bullets were fired through 7.62 mm SLR and 7.62 mm LMG from 50 m range, they penetrated through 30 mm and 50 mm thick panels but could not penetrate through 75 mm and 100 mm thick panels and in this case the depth of penetration observed was 35 mm only. Minimum 10 mm and maximum 20 mm diameter holes were formed with all three weapons. A 75 mmx100 mm size spalling was seen on front and rear side of the panel of 30 mm and 50 mm thickness and in case of 75mm and 100 mm thickness the spalling was noticed only on front side around the hole and no crack formation was observed any where in the panel. 3. Another observation recorded during the testing was that when 30 mm and 50 mm thick panels were placed together in parallel one behind the other with a gap of 15 mm and bullets fired from 50 m range with all three weapons i.e. 9 mm Machine carbine, '7.62 mm SLR, 7.62 mm LMG, the bullets penetrated through the front panel but could not penetrate through the rear panel and there was not even a trace of any penetration. 4. The value of punching shear strength for panel P7 and P8 has been found to be 75 Mpa under very high rate of strain loading. This value seems to be on a higher side hence further investigation are needed.