On the mechanics of the global bending collapse of circular tubes under dynamic axial load—Dynamic buckling transition (original) (raw)
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International Journal of Impact Engineering, 2004
The transition between progressive and global buckling of axially loaded aluminium extrusions in alloy AA6060 temper T6 was studied by quasi-static and dynamic tests. The primary variables in the tests were the local (b=h ¼ 17:78-40) and global (L=b ¼ 5-24) slenderness of the extruded members and the impact velocity. The critical global slenderness is defined as the slenderness where direct global buckling or a transition from progressive to global buckling occurs. In the quasi-static tests and for an impact velocity of 13 m/s, the critical global slenderness was found to be an increasing function of the local slenderness. In contrast, the critical global slenderness was a decreasing function of the local slenderness when the impact velocity was 20 m/s. The energy absorption was found to be very dependent on the collapse mode. Significantly more energy is absorbed in the progressive buckling mode than in the global bending mode. In the case of transition from progressive to global buckling, the energy absorption depends on the time of transition. The difference in energy absorption between the different modes decreases for increasing impact velocity due to inertia forces preventing the direct global buckling mode and the early transition from progressive to global buckling.
Plastic Collapse Analysis of Slender Circular Tubes Subjected to Large Deformation Pure Bending
Advances in Structural Engineering, 2002
This paper describes a series of tests to failure of fix-ended tubular braces subjected to cyclic concentric axial loading. The braces were made from cold-formed steel grade C350L0 ͑350 MPa nominal yield stress͒ circular hollow sections ͑CHS͒. Nine different diameter-to-thickness ratios in the range of 19ϽD/tϽ56 that have a moderate member slenderness in the range of 25ϽKL/rϽ41 were tested. The effects of three loading protocols on the inelastic hysteresis behavior of the CHS braces were examined. The CHS braces exhibited stable hysteresis behavior up to local buckling, and then showed considerable degradation in strength and ductility depending on KL/r and D/t ratios. First-cycle buckling loads were compared with design loads predicted using a number of steel specifications. The effects of section and member slenderness on strength, ductility, and energy absorption capacity of the braces were examined. The structure response factor ͑ductility index͒ was determined and used to derive new section slenderness limits suitable for seismic design.
International Journal of Impact Engineering, 2004
Dynamic elastic-plastic buckling of thin-walled square tubes is studied from the viewpoint of elasticplastic stress wave propagation, which originates from an axial impact loading. The influence of the impact velocity and the striking mass on the development of the buckling shape is discussed when considering the transient deformation process. It is shown that the maximum load, which results from a high velocity impact load and occurs at t ¼ 0; is a function of the impact velocity and is related to the speed of the elastic-plastic stress waves propagating along the tube. The predictions for the initiation of buckling based on a numerical simulation of the axial impact of strain rate insensitive square tubes using the FE code ABAQUS show good agreement with the results from experiments on aluminium alloy tubes impacted at various initial velocities. A comparison between the buckling initiation in square tubes and geometrically equivalent circular tubes reveals differences in the response, which are attributed to the stress wave propagation phenomena and to the structural differences between the two structures.
Bending collapse of thin-walled circular tubes and computational application
This paper focuses on describing the bending collapse behavior of thin-walled circular tubes. In this paper, global energy equilibrium theory is applied to derive the relationship between the applied moment and the bending angle of circular tubes. A general bending collapse mode of circular tubes is referenced for the derivation, and it is assumed that during bending crush, all impact energy is absorbed and distributed along the hinge lines. After obtaining the relationship, it is compared to a published theory of tubular structure's bending resistance, which was obtained from analytical and experimental studies. The derived bending resistance is then applied to generate simplified circular tube models, which have different cross-sections and are made of different materials. Crashworthiness analyses are performed on these simplified models as well as detailed tube models, and the crash results are compared to verify the efficiency of the generated simplified model and the accuracy of the derived tube's bending resistance. All the problems involved in this paper are solved by means of LS-DYNA. r
An Analysis Of Collapse Mechanism Of Thin- Walled Circular Tubes Subjected To Bending
2007
Circular tubes have been widely used as structural members in engineering application. Therefore, its collapse behavior has been studied for many decades, focusing on its energy absorption characteristics. In order to predict the collapse behavior of members, one could rely on the use of finite element codes or experiments. These tools are helpful and high accuracy but costly and require extensive running time. Therefore, an approximating model of tubes collapse mechanism is an alternative for early step of design. This paper is also aimed to develop a closed-form solution of thin-walled circular tube subjected to bending. It has extended the Elchalakani et al.-s model (Int. J. Mech. Sci.2002; 44:1117-1143) to include the rate of energy dissipation of rolling hinge in the circumferential direction. The 3-D geometrical collapse mechanism was analyzed by adding the oblique hinge lines along the longitudinal tube within the length of plastically deforming zone. The model was based on t...
Dynamic progressive buckling of circular and square tubes
International Journal of Impact Engineering, 1986
Smnmary--A series of over 120 axial crushing tests were conducted on circular and square steel tubes loaded either statically or dynamically. Approximate theoretical predictions for static and dynamic progressive buckling are developed. Fair agreement with the experimental results is achieved provided the effective crushing distance is taken into account and the influence of material strain rate sensitivity is retained for dynamic loads.
International Journal of Mechanical Sciences, 2013
The progressive collapse of tubular structures under axial loading is a challenging problem in mechanics. Due to the nonlinearities in large plastic deformation, such a problem can only be solved case by case under the assumption of an appropriate collapse mechanism. In this paper, a relationship between the progressive collapse of an axially loaded tube and the initial buckling of its windowed counterpart is presented. Numerical investigation was performed on the axial crushing of triangular, square and pentagonal tubes and the initial buckling modes of the corresponding windowed tubes. Results show that at the critical symmetric buckling mode, the theoretical mean crushing force of the angle-shaped column in the windowed tube matches very well with the actual mean crushing force of the conventional one. This relationship is crucial to the development of a generalized method for progressive collapse without assuming collapse mechanism. Based on it, an empirical equation on the mean crushing force of axially loaded square tubes is presented. The mean crushing forces predicted by this equation are in good agreement with the experimental results and theoretical values.
Effect of annealing, size and cut-outs on axial collapse behaviour of circular tubes
International Journal of Mechanical Sciences, 1993
Axial compression tests were performed on round tubes of different sizes and made of aluminium and mild steel, both in as-received and annealed conditions. Length to diameter and diameter to thickness ratios of these tubes were varied in different tests, and cut-outs in the form of circular holes, varying in diameter, number and position, were laterally drilled in them. Typical histories of their deformation and load-compression curves are presented and the influence thereon of the annealing process, the tube size, or the cut-outs is discussed. Relations are presented to describe these influences and to express the first peak and mean collapse loads in terms of the Vickers hardness number. It is seen that the presence of holes in the tubes alters their mode of collapse and, as a consequence, affords the possibility of avoiding Euler buckling even when relatively much longer tubes are employed.
Finite Element Analysis of Collapse of Metallic Tubes
Defence science journal
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 code has 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 deforming tube material was modelled as rigid-visco-plastic. Development of different modes of collapse was investigated experimentally and computationally. The experimental load-compression curves and 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 are capable of predicting the modes of collapse.
Non-linear Finite Element Analysis of Bitubal Circular Tubes for Progressive and Bending Collapses
This paper presents non-linear finite element analysis to carry out the dynamic response of foam-filled double circular tubes for axial progressive and global bending collapse modes. Some aspects were considered to investigate the crashworthiness capability of cylindrical tube for instance geometry, material and loading parameters. In addition, three types of structures namely empty double tubes (ED), foam-filled double tubes (FD), and foam-filled single tubes (FS) were observed under oblique impact. Crashworthiness parameters were determined in the numerical solution after validated with experiment and theoretical results in relevant references. Moreover, it is evident that the crash ability of the foam-filled double tube is better than the other structures. Finally, the main outcome of this study is the new design information of different tube configurations as energy absorber where two collapse modes are expected.