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Gupta, N. K.

	Normal and oblique impacts of hard projectile on single and layered plates : An experimental study Author : Madhu, V.;Bhat, Balakrishna T.;Gupta, N. K. Source : Defence Science Journal ; Vol:53(2) ; 2003 ; pp 147-155 Subject : 620.1 Material Science and Technology;623 Military Science and Engineering;623.4 Armaments and Ballistics;531.55 Projectiles Keywords : Projectiles;Normal impact;Oblique impact;Simulations;Layered plates;Target damage;Ballistic limit;Ballistics;Residual velocity;Perforation;Multilayered targets Abstract : The phenomenon of ordnance velocity impact of projectile on single and layered plates is of interest for many applications. In this paper. an experimental study of normal and oblique impacts or an ogive shaped, hard steel projectile on single and layered plates of mild steel and aluminium is presented. The projectiles were fired at an impact velocity of about 820 ms-1. The plate thickness was varied in the range 10 mm to 40 mm and the ratio of plate thickness to the diameter of the projectile varied in the range 1.5 to 13.0. Observations on target damage and measurements of incident and residual velocities for different angles of impact are presented. Plate thickness t*, for which the incident velocity is the ballistic limit, is determined. Computer simulations were carried out using a hydrodynamic code to simulate the normal impact of a projectile and compared these with the experimental results. Experiments were performed to evaluate the response of these plates of intermediate thickness when layered. and the results were compared to the results of single plate of same total thickness.
	Influence of Polymer Restraint on Ballistic Performance of Alumina Ceramic Tiles Author : Reddy, P. R. S.;Madhu, V.;Ramanjaneyulu, K.;Balakrishna Bhat, T.;Jayaraman, K.;Gupta, N. K. Source : Defence Science Journal ; Vol:58(2) ; 2008 ; pp 264-274 Subject : Keywords : Alumina ceramic;Ballistic impact;Polymer fibres;Confinement;Projectile Abstract : Influence of Polymer Restraint on Ballistic Performance of Alumina Ceramic Tiles
	Analysis of axisymmetric crushing of frusta Author : Khan, M. M. A.;Abbas, H.;Gupta, N. K. Source : Defence Science Journal ; Vol:53(1) ; 2003 ; pp 41-50 Subject : 620.1 Material Science and Technology Keywords : Thin walled structures;Energy absorbers;Cylindrical tubes;Frusta;Energy absorbing device;Curved fold model;Axisymmetric crushing Abstract : "The paper presents a curved-fold model with variable straight length for the axisymmetric crushing of thin frusta. The folding considered in the model is partly inside and partly outside. The variation of circumferential strain during the formation of a fold has been taken into account. The size of the fold and mean, as well as variation of crushing load, has been computed mathematically. The study is purely analytical and does not involve any empirical constant; and hence, can be used in general. The model's predictions have been compared with experimental results and a reasonably good agreement has been observed. "
	Numerical Simulation of Projectile Impact on Mild Steel Armour Plates using LS-DYNA: Part I: Validation Author : Deb, A.;Raguraman, M.;Gupta, N. K.;Madhu, V. Source : Defence Science Journal ; Vol:58(3) ; 2008 ; pp 422-432 Subject : 669 Metallurgy;66 Chemical Technology Keywords : Projectile;Mild steel plate;Ballistic impact;Simulation;LS-DYNA Abstract : The paper describes the simulation of impact of jacketed projectiles on steel armour plates using explicit finite element analysis as implemented in LS-DYNA. Validation of numerical modelling includes a comprehensive mesh convergence study leading to insights not previously reported in literature, using shell, solid, and axisymmetric elements for representing target plates. It is shown for a number of cases that with a proper choice of contact algorithm, element size, and strain rate-dependent material properties, computed projectile residual velocities can match closely with corresponding test-based values. The modelling requirements are arrived at by correlating against published test residual velocities1 for variants of mild steel plates (designated as MS1, MS2 and MS3) of different thicknesses at impact velocities in the range of ~820-870 m/s. Using the validated numerical procedure, a number of parametric studies such as the effect of projectile shape and geometric aspect ratios as well as plate thickness on residual velocity have been carried out and presented in Part II of the current paper.
	Adaptive finite element analysis of plastic deformation of plates under projectile impact Author : Prakash, T.;Sekhon , G. S.;Gupta, N. K. Source : Defence Science Journal ; Vol:53(1) ; 2003 ; pp 57-65 Subject : 620.1 Material Science and Technology Keywords : Finite element analysis;Aluminium plates;Projectile impact ;Closed form solutions;Plasticity;Metal plates;Flow formulation;Plastic deformation Abstract : "This paper deals with the finite-element analysis of plastic deformation of plates during normal impact of projectile on plates, The finite element method implemented here is based on the flow formulation of plasticity. During projectile impact the geometrical configuration of domain is progressively altered that generally causes distortion of mesh. It affects the accuracy of finite-element solution, Hence, a posteriori error estimation for the computed finite-element solution has been incorporated to capture the zones of high stress and strain gradients. The h-refinement of the mesh is carried out over such domain to limit the solution error, Two projectile impact problems on a circular aluminium plate-one by a blunt-end projectile and another by a hemi-spherical-headed projectile-are analysed to illustrate the proposed method. "
	Behaviour of Thin Aluminium Plates Subjected to Impact by Ogive-nosed Projectiles Author : Iqbal, M. A.;Gupta, N. K. ;Sekhon, G. S. Source : Defence Science Journal ; Vol:56(5) ; 2006 ; pp 841-852 Subject : 620.1 Material Science and Technology Keywords : Ogive-nosed projectiles;Perforation;Adaptive meshing;Aspect ratio;Johnson-Cook model Abstract : A pneumatic gas gun has been used to fire ogive-nosed projectiles on aluminium plates (1mm) at varying impact velocities above the ballistic limit. Impact and residual velocities have been measured. Deformation of the target plate was studied. Experimental results formed the basis of a subsequent finite element analysis of the problem using the ABAQUS 6.3 code. The Johnson-Cook plastic flow and fracture model available in the code were utilised. Explicit finite element analysis has been performed to model the perforation phenomenon. Numerical results were significantly improved by reducing the element size up to a certain level beyond which no significant variation in the results was observed. Adaptive meshing has been found to be useful in obtaining the accurate results and avoiding the problem of premature termination of the program due to excessive element distortion. Experimental and numerical results are compared and a good agreement between the two has been found.
	Finite Element Analysis of Collapse of Metallic Tubes Author : Gupta, P. K.;Gupta, N. K.;Sekhon, G. S. Source : Defence Science Journal ; Vol:58(1) ; 2008 ; pp 34-45 Subject : 53 Applied Physics;532 Fluid Mechanics Keywords : Metallic tubes;Quasi-static loading;Mode of deformation;FORGE2;Energy-absorbing devices Abstract : Quasi-static axial and lateral compression tests were conducted on aluminium tubes of circular, rectangular, and square cross sections on a universal testing machine (Instron model 1197). During the compression process, different tubes were collapsed in different modes of collapse. These compression processes were also modelled using FORGE2 finite element code. The code has the capabilities of automatic mesh generation, modelling of die, creation of material data file, carrying out the finite element computations, and post-processing of results. The deforming tube material was modelled as rigid-visco-plastic. Development of different modes of collapse was investigated experimentally and computationally. The experimental load-compression curves and deformed shapes are compared with the computed results and found in good agreement. It is found that the proposed finite element models of the different compression processes are capable of predicting the modes of collapse.
	Oblique impact of projectile on thin aluminium plates Author : Khan, W. U.;Gupta, N. K. ;Ansari, R. Source : Defence Science Journal ; Vol:53(2) ; 2003 ; pp 139-145 Subject : 620.1 Material Science and Technology;623.4 Armaments and Ballistics;531.55 Projectiles Keywords : Oblique impact;Impact velocity;Projectiles;Ballistic limit;Residual velocity;Plates;Aluminium plates;Analytical model;Projectile velocity Abstract : "Experiments were performed, wherein cylindrical projectiles made of hardened steel were impacted on commercially available aluminium plates at different angles. Projectiles were of 12.8 mm diameter and plates were of 0.81 mm, 1.52mm and 1.91mm thicknesses. Based on the experimental results, an analytical model has been developed to predict the residual velocity of the projectile and the ballistic limit of the plate. "
	Perforation of Layered Composite Plates by Impactors of Different Nose Shapes Author : Velmurugan, R.;Gupta, N. K. Source : Defence Science Journal ; Vol:58(2) ; 2008 ; pp 227-237 Subject : Keywords : Composite plates;Penetration;Nose shapes;Energy absorption Abstract : Conical and hemispherical nose-shaped cylindrical impactors have been used in drop weight impact experiments on 3.1 mm CSM-polyester laminated plates. Based on experimental results, various failure mechanisms and energy absorbed in different failure modes are identified and calculated. It is found that the damage area beyond a certain value of impact energy does not increase. The perforation geometry is the same as that of the impactor irrespective of increased crack length, and complete rotation of petals takes place at impactors radius. It is also observed that the crack length increases with decrease in contact area. But, when the nose is sharp (5 mm hemispherical nose), there is no extended crack beyond perforated region. Blunt nosed (truncated conical impactor with 10 mm nose dia) impactors cause more number of petals/cracks than 10 mm hemispherical nosed impactor and less than 5 mm hemispherical nosed impactor. The petals formed by a cylindrical impactor with 40 mm hemispherical nose are unequal in size, whereas in the case of conical impactors, these are equal. At lower energies, blunt nosed impactors cause more delamination than the hemispherical ones, and at higher energy, it is the reverse. It is found that there exist many visible concentric circular ring hinge mechanisms at the top surface of plates.