Experimental and analytical study of ballistic resistance of ceramic-polyurea-metal compound targets

نوع: Type: thesis

مقطع: Segment: phd

عنوان: Title: Experimental and analytical study of ballistic resistance of ceramic-polyurea-metal compound targets

ارائه دهنده: Provider: Saman Jafari

اساتید راهنما: Supervisors: Dr. Ali Alavi Nia

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees: Dr. Hossein Khodarahmi, Dr. Hashem Mazaheri, Dr. Mojtabi Yazdani

زمان و تاریخ ارائه: Time and date of presentation: 2024

مکان ارائه: Place of presentation: Faculty of Engineering

چکیده: Abstract: Composite targets are widely used in the field of mechanical engineering, including the field of ballistics. In this thesis, the ballistic resistance of composite targets with ceramic-polyurea-aluminum layers, against the impact of a projectile with a flat nose, has been investigated both experimentally and analytically. Experimental tests were carried out to understand the chemical properties and mechanical behavior of the materials of the target layers, projectile, and also to evaluate the ballistic resistance of composite targets. In order to evaluate ballistic resistance, ballistic tests were designed using Taguchi design method in Minitab software. In this thesis, two gas-guns were used for ballistic tests. One of the devices had a 3 m length with a caliber of 11 mm, in which the gas is guided to the back of the projectile by a solenoid valve. In another device with a caliber of 25 mm and a length of 6 m, the gas is discharged based on the destruction of the rapture disc at a certain pressure. From the ballistic tests, important ballistic parameters including damage in different layers of the target and projectile, projectile residual velocity, target energy absorption, aluminum hole diameter and ballistic limit velocity were evaluated. It was observed that due to the impact of the projectile with the ceramic layer, cracks are created on the back surface of the ceramic and these cracks grow on average angle of 48 degrees towards the front surface of the ceramic, finally a cone-crack is created. After the passage of the projectile, polyurea compensates a large amount of its initial elongation and the diameter of the hole created during the perforation reduced. A significant amount of ceramic fragments was absorbed by polyurea. Damage mechanisms such as dishing, petalling, dishing, fracture and cracks were also observed for aluminum layers. The dishing of the aluminum (caused by the projectile pressure) increased with the decrease of the impact velocity, also the diameter of the hole of the aluminum layer decreased with the increase of the impact velocity. Among the targets investigated in the experimental method, the target with code CPA1 absorbed the least energy and the target with code CPA5 absorbed the most energy. Also, based on the experimental ballistic limit velocity curves, it was observed that the target with code CPA1 has the least ballistic limit velocity. For a number of targets (targets with codes CPA5, CPA7, CPA8 and CPA9), it was not possible to conduct ballistic tests due to the limitation in projectile velocity. Therefore, to investigation the ballistic resistance of these targets, simulation was done in LS-Dyna software and its results were also used in optimization. Using the simulation, the residual velocity of the projectile was extracted for each target and compared with the experimental data. After ensuring the correctness of the simulation, the values of ballistic limit velocities were extracted and these results were used in optimization and theory. Based on the numerical results, it was determined that the target with code CPA7 has the greatest ballistic limit velocity and the highest strength. Also, in optimization and theoretical analysis, it was observed that the greatest decrease in velocity of projectile occurs when the projectile impacted with ceramic. Based on the experimental results, approximately 56.3% of the initial velocity of the projectile is reduced by ceramics, which is 25.9% and 17.8% for aluminum and polyurea, respectively. In order to more accurately determine the effect of the thickness of each layer on the objective functions and also to find a target with optimal thickness (that has both maximum energy absorption and minimum mass) optimization was done. Three objective functions of absorbed energy, mass and the ratio of absorbed energy per target mass were investigated in the optimization. Based on the optimization results, ceramic has the maximum effect in increasing the strength function with 64.37%; this effect is 13.03% and 22.54% for polyurea and aluminum, respectively. The ceramic layer increased the target mass by 55.93%, which is 14.34% for polyurea and 29.79% for aluminum. Also, ceramic with 80.22%, has the greatest effect in increasing the ratio of absorbed energy per target mass, which was equal to 9.56 and 10.21% for aluminum and polyurea, respectively. The results showed that polyurea has more effect than aluminum in increasing the ratio of absorbed energy to target mass. In the theoretical analysis, due to the large difference between the results of the Florence's equations and the experimental results, a number of parameters were modified, including the modification of the large radius value of the conical crack, the modification of the ceramic mass and strength. By modifying Florence's equation for two-layer targets, its difference with the experimental and analytical results of other references decreased and reached from 53.9% and 59.5% to 9.1% and 11.8%, respectively. According to the improvement of the modified Florence equations, this equation was extended for three-layer ceramic-polyurea-aluminum composite targets and a new relationship was derived to predict the ballistic limit velocity of these targets. The results of the new equation were compared with the experimental results obtained from the present study and it was observed that the maximum difference with the experimental results is 19.30%. By optimization, the thickness for the three-layer target with the highest ratio of absorbed energy per target mass for ceramic, polyurea, and aluminum was obtained as 11, 6, and 4 mm, respectively

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