In an optimal design, more often than not, an initial configuration of a structure must be modified several times to provide the optimal arrangement. The objective of the project is to develop and use a genetic algorithm to find such as arrangement for multi-layered shields.
When the nature of loading is known, systematic optimisation methods such as genetic algorithm could help find the best solution through an iterative process. It is therefore essential to use a robust optimisation scheme along with prior knowledge of the nature of loading on the structure to provide a heuristic algorithm to solve for best response. A plate of a given thickness (t) subjected to a particular ballistic threat has a certain ballistic limit (V50) and offers certain level of energy absorption. If the same plate is replaced by a set of plates of thicknesses t1 to tN , where N denotes the number of layers, in such a way that t=t1+t2+…tN, one can increase ballistic limit and energy absorption through correct selection of N-1 independent thickness variables for the same weight of the system.
DEPARTMENT OF MECHANICAL & AEROSPACE ENGINEERING Module Code: ME3309-ME3399 Module Title: Major Individual Project Module Leader: Mrs Petra Gratton Assessment Title: Project Proposal and Methodology Report Module Weighting: 15% Ballistic impact response of multi-layered shields Sanjeet Shokeen Student ID: 1733044 Project supervisor: Dr Arash Soleiman Fallah Table of Contents Abstract3 1.0Aim of the project4 2.0Objectives of the project4 3.0Context of the project4 4.0Background to the project5 5.0Methods to be adopted in carrying out the project7 6.0Risk assessment10 7.0Project management10 8.0Ethical approval11 9.0Resource requirements11 10.0References12 Abstract Nomenclature: NIJ = National Institute of Justice NABIS = National Ballistics Intelligence Service VG = Vest Guard BLV = Ballistic Limit Value is the ballistic limit is the projectile constant determined experimentally is the density of the laminate is the static linear compression elastic limit is the diameter of the projectile is the thickness of the laminate is the mass of the projectile is the wave velocity is the young’s modulus is the bulk density C is the speed of light is the poisson’s ratio Aim of the project To create and train a heuristic algorithm to improve the ballistic limit of a multi-layered shield using Matlab and Ansys to obtain the best arrangement for ‘n’ no. of plates. This study aims to determine the energy absorption properties and Backface signature of a material. Objectives of the project The objectives to be met in order to reach the aim of this project are: · Obtain the best arrangement to increase the ballistic limit of ‘6’ multi-layered aluminium (Al6061) shields. · Obtain the best arrangement to increase the energy absorption capacity of ‘6’ multi-layered aluminium (Al6061) shields. · Obtain the best arrangement to minimise the Backface signature of ‘6’ multi-layered aluminium (Al6061) shields. · Reduce the manufacturing costs of aluminium (Al6061) multi-layered shields Context of the project In recent years, the ongoing threat of ammunition and explosively formed projectiles to civil and military structures has increased the need to optimise protective structures. (E.A. Flores-Johnson, 2011) There is an increased risk due to vast development in the manufacturing and technology of the projectiles which has raised concern to yield better armours and shields. Aluminium alloys have been the primary material of choice for the production of the fuselage, wing and other supporting structure for the commercial airliners and military cargo and transport since about 1930. (E.A.StarkeJr., 1996) Although, polymer matrix composites are used in the high-performance military aircraft Aluminium alloy is still the best choice for commercial and cargo transportation which makes this topic a subject of intensive research due to increased crime and violence in the world. Multi-layered shields are used in different places like School windows and doors, High Commissions and Embassies and other organisations where security and confidentiality are top priorities. These shields are also used to manufacture storage safes and a lot of other safety tools which makes it critical to further research and develop the technology. Although there are a lot of studies dealing with Ballistic response of multi-layered shields, their scope is limited when it comes to Aluminium Al6061 alloy with a spherical projectile. Hence it remains an open research topic since conclusive results of its effectiveness have not been obtained to date. This project makes a key contribution to the multi-layered shields technology. It helps to improve the technology by explaining the energy absorption effects of Aluminium Al6061 alloy and also creates the best arrangement for the plates to improve the ballistic limit whilst minimising the backface signature effects. Assumptions: In this project, 1. The material used is Aluminium alloy Al6061. 2. The shape of the projectile is spherical. 3. maximum of 6 plates will be used to match the total thickness. Limitations: 1) This project does not include the practical testing of the configuration obtained for Aluminium Al6061 multi-layered shield. Results and conclusion solemnly rely on the 3-D Numerical simulations performed using Ansys. 2) A particular ballistic threat with a spherical velocity and response of a multi-layered Aluminium Al6061 shield with a maximum of 6 plates to match the total thickness have been studied. Background to the project Introduction This project includes detailed analytical, numerical and simulated investigation to illuminate changes of the order of the plates of different thickness on the ballistic performance of aluminium shields at high-speed impact and studies dealing with analytical methods for the optimization of multi-layered aluminium shields. Important features of this project are that · It gives a detailed explanation and simulation results of a high-speed spherical projectile impact response on a multi-layered aluminium shield with changing the order of the plates. Although, there are many studies available on Ballistic impact response none of them covers the response of aluminium with a spherical projectile which makes this topic open for further research. · This study will help reduce the manufacturing cost of multi-layered shields by educating manufacturers on the best arrangement for the shield and also reducing the material used. The project also focuses on keeping the cost minimum during the testing phase of multi-layered shields as it helps a lot to reduce overall the cost of the product. It focuses on delivering the testing results as quick as possible to minimise the time consumption. · Results from the analysis carried out will be helpful to understand the behaviour of aluminium multi-layered shields when stroked against spherical projectiles as it provides a detailed explanation and 3-D figures and numerical simulations. · It helps to increase the strength of the components made out of aluminium alloys like an aircraft fuselage, wings and many other parts by providing a better arrangement of multi-layered shields which can be used by manufacturers to produce better designs and structures. 4.2 NIJ Testing: (E.Frank, 1986) · Two different types of Ballistic tests are utilised to test the armour’s performance. The first test is the backfire signature test which calculates the performance of the armour against blunt force trauma and perforation. During the test, if single round penetrates the panel the structure is deemed to fail. It is carried out using clay where clay backing material must be less than 44mm. · The second type of testing conducted is ballistic limits deformation tests which measure its ballistic performance. Here multiple panels can be used to complete the tests. The testing velocity for subsequent projectiles varies depending upon the previous impact. Armours are tested for thermal conditions and also in submerged conditions to test the durability and capacity. · To keep improving the technology of multi-layered shields and armours it is important to research more and carry out experiments for a strong understanding of ballistic limit dynamics and energy absorption. 4.3 Existing Literature: Previous studies show that For the shields consisting of several plates with the same density but having different values of distortion pressure perforated, Ballistic limit value (BLV) of the armour can be increased if two adjacent plates are placed in a way such that value of the distortion pressure for the first plate is smaller than that of the second plate. The maximum ballistic limit value of armour is achieved when plates are arranged in increasing order of their distortion pressure values and minimum ballistic limit value is achieved when plates are arranged in their decreasing order of distortion pressure values. (G.Ben-Dor, 2014) Following case studies provide the results and conclusion for experiments carried out in past. 1) Penetration resistance of double-layered sheet structures: (Nysmith, 1968) · Small Pyrex glass spherical projectiles were made to strike into aluminium double-layered sheet at velocity 8.8Km/s to determine the effects of total sheet thickness and sheet spacing upon penetration resistance. · The Ballistic limit for two equally thick Al sheets was found to increase with an increase in total sheet thickness and sheet spacing. · In addition, the effectiveness of sheet spacing increase with the increase in projectile velocity whilst keeping the ratio of total sheet thickness to projectile diameter fixed. · It was determined that front-sheet hole diameter varies with the square root of the impact velocity. · It was concluded that at a given velocity the ratio of front sheet thickness to projectile causing maximum vaporization will be used as thickness for front sheet and remaining mass in the rear sheet for most efficient double-layered structure. 2) Ballistic performance of multi-layered metallic plates impacts by a 7.62-mm APM2 projectile. (E.A. Flores-Johnson, 2011) · An investigation was conducted to the test the Ballistic performance of monolithic, double and triple-layered metallic plates made of aluminium or steel or a combination of both. · The test shows that monolithic plates have a better ballistic performance than that of multi-layered plates made out of the same material. · Double layered plates with a thin front plate of aluminium and thick back steel plate exhibit greater resistance than multi-layer steel plates with similar area density. · It was concluded that further research should be carried out on the multi-layered target using different metallic material for better ballistic performance and weight savings. · They also found that reduction of resistance in multi-layered targets become more apparent as the no of plates is increased keeping the total thickness of the plate constant. 3) New results on ballistic performance of multi-layered metallic shields: (G.Ben-Dor, 2017) · This survey includes the analytical, numerical and experimental studies in which the effect of layering, spacing and change of the order of the plates have been considered leading to the Ballistic limit of the metallic shields against high-speed projectiles. · It was concluded that there are number of parameters that affect the penetration like the shape of the projectile, velocity, material, impact position and many more. · Further investigation has to carried out to determine the penetration laws and prepare a pattern · For sharp projectiles, layering and spacing decrease the ballistic performance of the shields and order of plates made from different material in the multi-layer shield may have a significant effect on the shield ballistic properties. · For blunt projectiles, layering and spacing have a negative impact on ballistic resistance but a variation of the order of layers manufactured from the same material but having different thickness affects ballistic resistance of the shields. All these studies were tested in laboratory conditions with real projectiles and final manufactured shields. These studies provide the actual tested results and help in better understanding of the ballistic limits, resistance, projectile penetration and backfire signature. Methods to be adopted in carrying out the project 5.1Methodology · To begin with, the project data sets will be extracted from the known historic experimental records of ballistic impact responses for different projectiles. Using previous journals and papers to study the existing researches and collecting data for ballistic impact responses of aluminium alloy (Al6061) and spherical projectile. Energy absorption properties of aluminium are very important to understand as it helps to build structures and shields with the better ballistic limit. · ‘Matlab Genetic Algorithm’ will be used to analyse the data and create heuristic algorithms which