| || Stress Intensity Factor using Finite Element Analysis in Rectangular Orthotropic Composite Annular Disk
Author : Ramamurthy, G. ;Ravinder Reddy, P.
Source : Defence Science Journal ; Vol:47(1) ; 1997 ; pp 55-63
Subject : 539.42 Fracture Mechanics;621 Mechanical Engineering
Keywords : Radial load ;Fracture mechanics;Stress intensity;Isoparametric elements
Abstract : The quadratic isoparametric elements which embody the inverse squareroot singularity were used to determine the stress intensity factor in an annular disk made of Boron-Epoxy composite material. The displacements and stresses were determined in a rectangular orthotropic composite annular disk using isoparametric finite elements. The singularity in the strain field was provided by means of 8-noded isoparametric elements (4-nodes at the four corners and four mid-side nodes each at l/4th distance from the edge). The results were obtained for various material properties and fibre orientation. The geometry of the annular disk was reported when subjected to a boundary radial and tangential. The r singularity was provided at the boundary of the circular hole and the rest of the annular disk was modelled with ordinary isoparametric elements. The apparent stress intensity factor (K/sub I/=) was computed from the stress data near the circular hole, when it was subjected to uniform tension. A curve was drawn for apparent stress intensity factor versus the distance from the crack edge and was extrapolated to r = 0, the actual stress intensity factor was found on the y-axis.
| || Impulsive Loading of Armour by High Explosive Squash Head Munition
Author : Deshpande, P. U.;Prabhu, V. D.;Prabhakaran, K. V.
Source : Defence Science Journal ; Vol:53(4) ; 2003 ; pp 357-366
Subject : 620.261 Explosives ;623.45 Ammunition
Keywords : HESH ammunition;Impulsive loading;Dynamic loading;Blast;Static loading;High explosive squash head munition;Explosive reactive armour;Scabbing;Spalling;Fracture mechanics
Abstract : Results obtained by theoretical modelling studies involving classical stress-strain theories, duly validated by experimental investigation in understanding the mechanism of impulsive loading (scabbing) and blast under dynamic and static conditions, are discussed. This concept has been used in designing a high explosive squash head ammunition being effective in defeating monolithic armour. Efforts have been made to carry out an in-depth study in understanding the mechanism of scabbing under static and dynamic (live firing) conditions. For this purpose, a one-dimensional computer code has been used to predict the spread of explosive against time on the target. The simulations were carried out using a 2-D Lagrangian hydrodynamic code for scabbing effect. The blast effect that follows under static and dynamic conditions has also been studied. Blast parameters have been computed in terms of TNT equivalent and compared with experimental results. The events occurring during impulsive loading of 135 mm monolithic rolled homogenous armour have been illustrated.