M.A. Iqbal

Reliability analysis of nuclear containment without metallic liners against jet aircraft crash

The present study presents a methodology for detailed reliability analysis of nuclear containment without metallic liners against aircraft crash. For this purpose, a nonlinear limit state function has been derived using violation of tolerable crack width as failure criterion. This criterion has been considered as failure criterion because radioactive radiations may come out if size of crack becomes more than the tolerable crack width. The derived limit state uses the response of containment that has been obtained from a detailed dynamic analysis of nuclear containment under an impact of a large size Boeing jet aircraft. Using this response in conjunction with limit state function, the reliabilities and probabilities of failures are obtained at a number of vulnerable locations employing an efficient first-order reliability method (FORM). These values of reliability and probability of failure at various vulnerable locations are then used for the estimation of conditional and annual reliabilities of nuclear containment as a function of its location from the airport. To study the influence of the various random variables on containment reliability the sensitivity analysis has been performed. Some parametric studies have also been included to obtain the results of field and academic interest.

BUCKLING ANALYSIS OF LAMINATED SANDWICH BEAM WITH SOFT CORE

Stability analysis of laminated soft core sandwich beam has been studied by a C0 FE model developed by the authors based on higher order zigzag theory (HOZT). The in-plane displacement variation is considered to be cubic for the face sheets and the core, while transverse displacement is quadratic within the core and constant in the faces beyond the core. The proposed model satisfies the condition of stress continuity at the layer interfaces and the zero stress condition at the top and bottom of the beam for transverse shear. Numerical examples are presented to illustrate the accuracy of the present model.

Ballistic resistance of mild steel plates of various thicknesses against 7.62 AP projectiles

The ballistic resistance of mild steel plates has been studied against 7.62 AP projectiles through numerical simulations using ABAQUS/Explicit commercial finite element package. The projectiles were impacted on 4.7, 6, 10, 12, 16, 20 and 25 mm thick target plates at varying incidence angles. The material parameters proposed by authors for the Johnson–Cook model were used to predict the material behavior of target, while the material behavior of projectile was incorporated from the available literature. The numerical results thus obtained have been compared with the experiments available in the literature. The experimental and numerical results with respect to failure mechanism, residual projectile velocity, and maximum angle for perforation and the effect of configurations on spacing and critical angle of ricochet have been compared. A close correlation between the experimental findings and the predicted results has been found. In general, the resistance of target has been found to increase with an increase in target obliquity. The critical angle of the projectile ricochet has been found to decrease with an increase in target thickness. The ballistic limit for all given thicknesses of mild steel targets has also been obtained numerically. The ballistic limit thus obtained has been used to calibrate the Recht–Ipson empirical model for calculating the residual projectile velocity corresponding to a given incidence velocity. Simulations were also done for three-layered target of 4.7- and 6-mm-thick plate and spacing was varied to study its effect on their ballistic resistance. The variation of spacing at normal impact was found to have an influence as long as the spacing was smaller than the projectile length.

Stability Analysis of Laminated Soft Core Sandwich Plates Using Higher Order Zig-Zag Plate Theory

C0 finite element model based on higher order zig-zag plate theory is used to study the stability analysis of laminated sandwich plates. The in-plane displacement field is obtained by superposing a global cubically varying displacement field on a zig-zag linearly varying displacement field with different slope in each layer. The transverse displacement assumes to have a quadratic variation within the core and constant in the faces. The conditions regarding transverse shear stress at layer interfaces and top and bottom are satisfied. Numerical examples covering different features of laminated sandwich plates are presented to illustrate the accuracy of the model.

Behavior of cantilever and counterfort retaining walls subjected to lateral earth pressure

Abstract Three-dimensional (3D) finite element simulations have been performed in order to study the response of cantilever and counterfort retaining walls subjected to lateral earth pressure using ABAQUS/Standard. Four retaining walls with different geometrical configurations were analyzed including three cantilever and one counterfort wall. The results thus obtained were compared, and the mechanics involved in the behavior of the retaining wall was discussed. The lateral displacement, vertical settlement, and stresses developed in each component of the retaining wall were studied and compared with the other walls. The choice of the retaining wall based on the economic analysis was also discussed and compared.

Response of Nuclear Containment Structure to Aircraft Crash

ABAQUS/Explicit finite element code was used to predict the response of BWR Mark III type containment against Boeing 707–320 aircraft crash. The damage plasticity model was employed to predict the behavior of concrete while the Johnson-Cook elasto-viscoplastic material model was used to incorporate the behavior of steel reinforcement. The loading of the aircraft was applied using a force history curve available in literature. The crash was considered to occur at two different locations i.e., at the midpoint of the cylindrical portion and at the junction of dome and cylinder. The midpoint of the cylindrical portion experienced more deformation. The results were compared with those of the studies available in literature and a close agreement between the two was found.

Impact response of thin aluminium plates and hemispherical shells

ABSTRACT An experimental and numerical investigation has been carried out to compare the ballistic performance and energy absorption characteristics of plate and hemispherical shells made of 1100-H12 aluminium against projectile impact. For direct comparison, the thickness (1 mm) and diameter (68, 100, 150 and 200 mm) of both the target were kept identical. With varying incidence velocity within the range of sub-ordnance velocity, two distinct shapes of nosed projectiles, ogive and blunt, were impacted normally at the centre and crown of the plates and shells, respectively.A pressure gun was employed to perform the ballistic test whereas the numerical simulations were carried out through commercial finite element code ABAQUS and a close correlation between the experimental and numerical findings was observed. The response of both the targets was investigated in terms of failure mechanics, global and local deformation, ballistic limit, residual velocity and energy absorption in plastic deformation against both the projectiles.

Effect of Platen Restraint on Stress–Strain Behavior of Concrete Under Uniaxial Compression: a Comparative Study

The stress-strain model of concrete depends on the degree of frictional resistance across the loading surfaces of a test specimen depending on the antifriction medium used during testing. This article presents a comparative study of platen restraint on the behavior of concrete under uniaxial compression based on an experimental investigation. The effect of four commercially available antifriction media (neoprene, polyvinyl chloride, teflon, and grease) with different layer thicknesses on platen restraint have been studied for a normal strength concrete and a relatively high-strength concrete. Subsequently, the effect of platen restraint has been quantified using the analogy of toughness. The experimental results indicate that post-ultimate response of concrete is significantly affected by platen restraint. It is shown that the stress–strain curve obtained from a conventional uniaxial compression test not only describes specimen/material behavior but also represents interaction between specimen and loading platen. Among the four antifriction media used in this investigation, grease is the most effective in reducing frictional resistance. Failure patterns of the concrete specimens for different antifriction media are also subsequently analyzed.

Effect of periphery fixity on ballistic limit of thin aluminum plate subjected to blunt and ogival projectile impact

Abstract Three-dimensional numerical simulations were carried out with the ABAQUS/explicit finite element code to study the influence of target boundary conditions on its ballistic limit. 1mm thick 1100-H12 aluminum target of 255 mm span diameter was hit by 19 mm diameter and 50.8 mm length blunt nosed projectile. The mass of the projectile was kept as 52.5 gm. The boundary condition effects on the ballistic limit were investigated by varying the target periphery boundary condition as fully clamped and partially clamped target (75%, 50% and 25%) subjected to projectile impact. The energy absorption and ballistic limit of the target was found to be significantly affected by the boundary conditions. Some of the finite element analysis results were compared with experimental and numerical results reported in international literature and a good agreement between the two was found.