P.K. Gupta

An analysis of external inversion of round tubes

Abstract An experimental and computational study of external inversion of round tubes over a die of circular profile is presented. Forming load–compression curves, energy–compression curves, deformed profiles, and contours of components of stress and strain tensors are presented and discussed. Predicted results are compared with those of experiment. Mechanics of the inversion process is discussed. Effect of process parameters on the inversion process is discussed.

A study of lateral collapse of square and rectangular metallic tubes

Abstract The paper presents an experimental and computational study of rectangular and square tubes made of aluminium and mild steel and subjected to quasi-static transverse loading. Deformed shapes at different stages, load–compression and energy–compression curves have been obtained experimentally. The deformation process was numerically simulated using finite element code FORGE2. The contours of different components of stress and strain rate tensors and nodal velocity have been plotted. Mechanics of deformation process, comparison of experimental and computed results and effect of process parameters on the mode of deformation are presented and discussed.

A study of fold formation in axisymmetric axial collapse of round tubes

Abstract Axial compression tests were performed on round tubes of different sizes made of aluminium and mild steel in an Instron machine. The diameter to thickness ratios were varied from 11.1 to 37.46 in the case of aluminium tubes, and from 11.65 to 30.67 for steel tubes and their length to diameter ratio was kept as 2. All these tubes deformed in the axisymmetric concertina mode. Typical histories of their deformation, load–compression curves and energy absorbing capacity are presented. The fold formation in axisymmetric concertina mode of deformation was analysed in detail by using the finite element code FORGE2. The material was modelled as rigid-viscoplastic. The experimental and computed results are compared. Typical contours of equivalent strain, equivalent strain rate and different stress components as well as energy dissipation mechanisms during formation of the first concertina fold are presented. Results presented are of help in understanding the nature of actual fold formation.

Study of concrete-filled unplasticized poly-vinyl chloride tubes in marine environment

This article presents an experimental study on columns prepared by filling reinforced concrete in unplasticized poly-vinyl chloride tubes exposed to artificial sea water prepared in the laboratory. Totally, 72 reinforced concrete-filled unplasticized poly-vinyl chloride tubular column specimens of length 800 mm were cast by filling the reinforced concrete in unplasticized poly-vinyl chloride tubes having 160, 200 and 225 mm diameters. The diameter-to-thickness ratio and length-to-diameter ratio of the specimens vary from 22.48 to 40.14 and 3.56 to 5, respectively. Out of 72 specimens, 36 specimens were converted to bare reinforced concrete columns by removing unplasticized poly-vinyl chloride tubes. In total, 18 reinforced concrete–filled unplasticized poly-vinyl chloride tubular and 18 bare reinforced concrete specimens were kept completely submerged in artificial sea water of salt concentration 20N for the period of 6 months while 36 specimens of reinforced concrete–filled unplasticized poly-vinyl chloride tubular were kept for 28 days after covering the top and bottom of specimens with thick polyethylene sheet to avoid evaporation of water. Out of these 36 reinforced concrete–filled unplasticized poly-vinyl chloride tubular specimens, 18 specimens were converted to bare specimens at the time of testing. All the specimens were tested by applying axial load on concrete core only to obtain load–displacement curves and modes of failure. No degradation in the strength and ductility of reinforced concrete–filled unplasticized poly-vinyl chloride tubular specimens was observed after submergence in sea water. It can be concluded that unplasticized poly-vinyl chloride tube provides a safety jacket to encased concrete core, and as a result improve strength, ductility.

Numerical study of confinement in short concrete filled steel tube columns

This study presents a numerical investigation into the behaviour of short concrete filled steel tubular (CFST) columns. Three Dimensional Nonlinear finite element analysis of the compression process is performed using commercial software ABAQUS v6.9 (2009). Steel tubes of different geometries and in-filled with different grades of concrete are chosen for modelling from literature. The proposed FE model is validated by comparing its results with those of the corresponding experimental specimens. The model is further used to study the variation of radial confining pressure fcp provided by the steel tube to the concrete core. It is observed that the value of fcp varies widely throughout the length of the CFST, with the values in the area adjacent to top and bottom platens being markedly higher than the values in-between due to the end restraint provided by the machine platens. This is in contrast to the present confined concrete model which uses a uniform value of confining pressure throughout the height. Effect of effective length of column and interfacial friction present between the platen and specimen are found to be negligible on behaviour of short CFST column.

Geometrical metallic shell behavior study under compression

The loading response of shell structures depends on their shapes. The individual shape behaves uniquely to the loading, and different shapes give different load displacement graphs. If these geometries are combined, then their load displacement graphs can be different. It may happen that their combined behavior can be harnessed to be used as better energy absorber in a controlled manner, which they cannot if they are used individually. Experiments were conducted on two separate geometries as well by joining them with weld. The first geometry was the top cylindrical and frusta bottom. The second geometry was the shape of inverted bell crater and half-spherical shells. Combining these two shapes produced the third geometrical shape. The large deformation was obtained by crushing these geometrical shells between two flat plates. The finite element analysis was used to simulate the crush phenomenon. The behavior of the geometrical shell to large deformation was understood with load displacement graph for different samples. The energy absorbed by the different samples was calculated and compared. The parameters, like material and thickness, were varied for the samples to see their effect on the large deformation behavior. Moreover, friction role is discussed on the crush phenomenon. This paper also gives an idea on the different parameters which can affect the energy-absorbing capacity of the combined geometrical shells.

Confinement of concrete columns with unplasticized Poly-vinyl chloride tubes

In this paper an experimental study is presented to investigate the effectiveness of UPVC tube for confinement of concrete columns. UPVC tubes having 140 mm, 160 mm and 200 mm external diameters were used to confine the concrete having compressive strength 20 MPa, 25 MPa and 40 MPa. The concrete has been designed using IS code 10262-1982(Reaffirmed -2004) (BIS:10262–1982, Reaffirmed -2004). The testing of the specimens was carried out on a displacement controlled Instron make Universal Testing Machine of 2500 kN capacity. During the experiments mode of deformation and corresponding load-compression curves were recorded and obtained results are compared with the existing models for confined concrete available in the literature. It is found that the predicted capacities of columns using different models are within ±6% of the experimental capacities. It is found that UPVC tubes can be effectively used for confinement of the concrete columns and to enhance their load capacity, ductility as well as energy absorbing capacity.

Finite Element Analysis of Metal Forming Problems Using Parallel Computing Technique

In this paper a finite element software by idealizing deforming material as rigid-viscoplastic is presented to study the two-dimensional large deformation axisymmeteric and plane strain problems. Comparing the predicted results with the corresponding results obtained using commercial softwares FORGE2 and ANSYS validates the software. A new parallel algorithm for matrix inversion method is proposed and implemented in the developed software on the platform of supercomputer PARAM 10000. Blocking and non-blocking communication mechanisms are used to communicate between master and slave processors and both are found equally effective. Developed parallel solver was also tested for its implementation in the analysis of three-dimensional metal forming problems. It was found that the solver performed efficiently and a Speedup of 5 to 8.5 for eight processors was obtained for different data sizes.

Numerical Investigation of Process Parameters on External Inversion of Thin-Walled Tubes

In this paper, a computational study of development of external inversion mode of deformation of round-metallic aluminum tubes over a fixed profile die is presented. Inversion mode of deformation is analyzed in detail by using a finite element code FORGE2. The proposed finite element model for this purpose idealizes the deformation as axisymmetric. Six-noded triangular elements are used to discretize the domain. The material is modeled as rigid-viscoplastic. Typical variations of the equivalent strain rate and equivalent strain along the length of the deforming tube are studied to predict the development of inversion mode of deformation. The influence of the friction present at the contact interface between the tube and the die is also examined to suggest a successful inversion of tube. Energy absorbed in overcoming the frictional stresses between the tube-die interfaces is compared with the total energy required in the inversion of tube. A few predicted results which include the geometry of inverted tube load-compression variation during inversion process are compared with their experimental counterparts to validate the computational model.

A study on inversion of metallic thin-walled conical shells

The paper presents an experimental and computational study of the inversion process of metallic thin-walled conical shells subjected to axial compression. The study mainly focuses on two aspects: firstly, to optimise the semi-apical angle of a cone to get a constant collapse load and secondly, to study the mechanics of the development of the inversion mode of collapse. Axial compression of aluminium thin-walled conical shells of semi-apical angles between 8° and 11° was performed on a universal testing machine Instron. An axisymmetric finite element computational model of the development of the inversion mode of collapse is also presented and analysed, using a non-linear finite element code FORGE2. Six-noded triangular elements are used for discretising the deforming shell domain. The material of the shells is idealised as rigid viscoplastic. Experimental and computed results are compared to validate the computational model. On the basis of the obtained results, the development of the axisymmetric inversion mode of collapse is presented, analysed and discussed.