Modelling and analysis of bi-layer ceramic–metal protective structures

• Main Author: Ahmad Serjouei
• Other Authors: Sridhar Idapalapati
• Format: Theses and Dissertations
• Language: English
• Published: 2014
• Subjects: DRNTU::Engineering::Mechanical engineering::Mechanics and dynamics
• Online Access: http://hdl.handle.net/10356/61767
• Institution: Nanyang Technological University

Technical ceramics due to their high specific hardness and compressive strength under pressure loading are attractive materials for armor structures. However, the low toughness of the ceramics is limiting their usage in practical designs. Adding a strong and tough plate at the back of the ceramic plate such as metal or polymer composite laminate, is one of the states of the art armor design that is extensively studied by researchers. Due to the cost of field experiments in defense industry, development of analytical, numerical/empirical models to estimate the ballistic velocity of armor systems by considering geometry of the projectile and target structure is gaining importance. Optimization of the armor design for either weight or thickness is also an important criterion. Furthermore, improving the toughness of the ceramic employing different means like adding metallic phases or pre-stressing them is of considerable interest. In the present thesis, a semi-analytical model is presented for impact of flat-ended (blunt) hard projectiles against ceramic–metal armor. Comprehensive numerical simulations are performed based on which it is shown that the projectile residual velocity and BLV satisfy the replica scaling laws. An empirical equation for the BLV is proposed whereby the influence of projectile and armor geometrical parameters on the BLV is explored. Experimental work is performed for validating the proposed semi-analytical model on alumina–aluminum armor system. A numerical model is then developed through matching with experimental results based on which variation of the length of the projectile with time and also with front plate and backing plate thicknesses is found. A generalized empirical model to estimate the BLV, as a function of geometrical and material parameters for ceramic–metal bi-layer armor systems impacted by a blunt projectile, is proposed. Comparison between results obtained from the empirical model for the BLV of ceramic–metal armor impacted by blunt projectiles, with the available experimental data is carried out. The proposed empirical BLV equations and the developed numerical model based on experimental results are employed for optimization of ceramic–metal armor systems, under blunt hard projectile impact, for given constraints of total thickness or areal density (mass per unit area) of the armor. A new analytical model, accounting for erosion and plastic deformation mechanisms, is proposed for the conical projectile impact onto bi-layer ceramic–metal armor system, extended based on Recht’s model for the blunt projectile impact onto a monolithic armor. The residual length of the projectile and the time taken for the erosion and plastic deformation are found. Finally, the effect of different types of pre-stress conditions such as radial, axial and hydrostatic on the penetration response of confined thick SiC ceramic armor under tungsten long rod impact is explored through AUTODYN based numerical simulations. It is shown that pressure below and near to the impact site of the confined ceramic target at the locations where damage initiates is important in the transition behavior from dwell to penetration for targets of various pre-stress states and of different pre-stress ratios.