| || Plasticity Methods in Protection and Safety of Industrial Plant and Structural Systems Against Extreme Dynamic Loading
Author : Jones, Norman
Source : Defence Science Journal ; Vol:58(2) ; 2008 ; pp 181-193
Keywords : Blast and impact loadings;Structural safety;Protection;Energy absorption;Perforation;Dynamic inelastic failure
Abstract : This paper provides an overview of the contributions that plastic methods of analysis can make to the protection of the public and the security of industrial plant against extreme dynamic loading events which involve explosive blast pressures or impact loadings from various projectiles. It is possible, by careful design, to absorb the external dynamic energies through large inelastic deformations of the structural members and specially designed energy-absorbing systems. Both the protection methods are examined briefly, together with some discussion on the dynamic properties of materials, including inelastic failure, and the impact perforation of ductile metal structures. Some phenomena are emphasised that are important for numerical finite-element schemes as well as theoretical methods of analysis.
| || Energy absorption characteristics of metallic and composite shells
Author : Velmurugan, R.;Gupta , N. K.
Source : Defence Science Journal ; Vol:53(2) ; 2003 ; pp 127-137
Subject : 620.1 Material Science and Technology;623.4 Armaments and Ballistics;678 Composite Materials
Keywords : Axial compression;Metallic tubes;Composite shells;Failure mode;Energy absorption;Post collapse behaviour
Abstract : Metallic and composite shells of different sizes and tubes were subjected to axial compression in an Instron Machine. Their progressive failure modes and energy absorption capacities have been studied. In the case of metallic shells, analytical expressions are derived to find the mean collapse load and the fold length based on the formation of plastic hinges. Theoretical results have been compared with experimental results wherever possible. The effect of internal folding on the post-collapse behaviour of round tubes has been discussed and expressions for fold length and post-collapse load compression curves are derived as a function of internal folding. Based on the experimental observations, analysis has been carried out to find the progressive crushing load and crush length in a cycle of round and conical shells. The shells are infilled with polyurethane foam and subjected to axial compression. The effect of foam on the crushing behaviour is also studied. Conical shells of different cone angles varied from 8.5" to 45" and the effect of cone angle on the crushing mode of the conical shells has been studied. Also, a comparative study of metallic and composite shells has been carried out based on the deformation and energy absorption characteristics. The different parameters considered for analysis include effective crushing length and total energy absorbed during the crushing process and the Euler buckling length in metallic shells.
| || 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
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.