Finite Element Analysis of Collapse of Metallic Tubes

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 codehas 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 deformingtube material was modelled as rigid-visco-plastic. Development of different modes of collapsewas investigated experimentally and computationally. The experimental load-compression curvesand 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 arecapable of predicting the modes of collapse

Energy Absorption Characteristics of Metallic and Composite Shells

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 byImpactors of Different Nose Shapes

Conical and hemispherical nose-shaped cylindrical impactors have been used in drop weightimpact 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. Theperforation geometry is the same as that of the impactor irrespective of increased crack length, andcomplete rotation of petals takes place at impactors radius. It is also observed that the crack lengthincreases with decrease in contact area. But, when the nose is sharp (5 mm hemispherical nose), thereis no extended crack beyond perforated region. Blunt nosed (truncated conical impactor with 10 mmnose dia) impactors cause more number of petals/cracks than 10 mm hemispherical nosed impactorand less than 5 mm hemispherical nosed impactor. The petals formed by a cylindrical impactor with40 mm hemispherical nose are unequal in size, whereas in the case of conical impactors, these areequal. At lower energies, blunt nosed impactors cause more delamination than the hemisphericalones, and at higher energy, it is the reverse. It is found that there exist many visible concentriccircular ring hinge mechanisms at the top surface of plates

Oblique Impact of Projectile on Thin Aluminium Plates

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

Adaptive Finite-element Analysis of Plastic Deformation of Plates under Projectile Impact

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

Analysis of Axisymmetric Crushing of Frusta

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.

Behaviour of Thin Aluminium Plates Subjected to Impact by Ogive-nosed Projectiles

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 havebeen measured. Deformation of the target plate was studied. Experimental results formed thebasis of a subsequent finite element analysis of the problem using the ABAQUS 6.3 code. TheJohnson-Cook plastic flow and fracture model available in the code were utilised. Explicit finiteelement analysis has been performed to model the perforation phenomenon. Numerical resultswere significantly improved by reducing the element size up to a certain level beyond which nosignificant variation in the results was observed. Adaptive meshing has been found to be usefulin obtaining the accurate results and avoiding the problem of premature termination of theprogram due to excessive element distortion. Experimental and numerical results are comparedand a good agreement between the two has been found