G.L. Viegelahn

Extensible plastic collapse of thin-wall frusta as energy absorbers

Abstract The crumpling of thin-walled frusta, under axial compression, in the ‘concertina’ mode is studied. The energy expended in bending at the plastic hinges and in stretching the metal between the hinges is minimized for the total decrease in height due to collapse. The thinning of the cross-section due to stretching is neglected. A theoretical model has been developed and numerical results are obtained that show the effect of slenderness, t/ D , and the semi-apical angle of the frusta. Good qualitative agreement in trends is exhibited when comparison with available experimental results is made.

The crumpling of steel thin-walled tubes and frusta under axial compression at elevated strain-rates: Some experimental results

Abstract Uniformly thin circular cylinders and frusta (truncated circular cones) of low carbon steel were subjected to axial loading at elevated strain-rates. Their initial axial length and the outside diameter of the cylinders and frusta (the larger top end) were kept constant whilst their uniform wall thickness was varied. The load-deformation or compression behaviour of the cylinders and frusta for the two semi-apical angles used, 5° and 10°, were recorded and the modes of collapse were observed and are discussed. Initial axisymmetric rings (‘ring’, ‘bellows’ or ‘concertina’ buckling) developed into non-symmetric ‘diamond’ patterns (elliptic, triangular and square, etc.) as loading progressed and initially non-symmetric diamond buckle patterns were observed to characterise the modes of frustum collapse.

On the inextensional axial collapse of thin PVC conical shells

Abstract Inextensional collapse mechanisms are presented for the axial crumpling of thin-walled circular cones and frusta (truncated circular cones). Shortening of the (thin) shell height is achieved by folding in a non-symmetric diamond mode about stationary circumferential and inclined plastic hinges; collapse proceeds progressively from the narrower end of the conical shell during the passage of a travelling hinge. Expressions for the various mean crushing loads, when collapsing frusta of rigid-perfectly-plastic material, are developed. Theoretical collapse modes and predicted loads are compared with those obtained experimentally by collapsing rigid PVC conical shells of constant axial length, of various wall-thicknesses and semi-apical angles, as well as metal (aluminium alloy and low-carbon steel) conical shells of similar geometry; agreement is found to be good.

Energy dissipation and associated failure modes when axially loading polygonal thin-walled cylinders

Abstract The crumpling mechanisms of thin-walled octagonal steel tubes subjected to axial static compression and their efficiency as energy absorbing components under impact conditions are investigated and compared with the equivalent circular and square tubes of same material. Both inextensional and extensible collapse mechanisms are theoretically analysed. Theoretically predicted values based on the deformation modes encountered, as well as experimentally obtained ones, are compared and found to be in good agreement.

Crashworthy Behaviour of Thin-Walled Tubes of Fibreglass Composite Materials Subjected to Axial Loading

In this paper we report on small scale modelling of fracture mechanisms and large scale deformation of fibre-reinforced composite materials when circular thin-walled tubes are subjected to axial collapse. Contrary to the mechanism of energy absorption in the case of ductile materials, energy absorption for brittle composite materials is achieved by material fragmentation, i.e., the mechanism of fracture dominates the phenomenon rather than the plastic deformation. The effect of composite material properties and the tube geometry on the crashworthy characteristics of the tubular structural components is investigated with the aim in mind of the cost-effective design of structural elements in vehicles.

The axial crushing of thin PVC tubes and frusta of square cross-section

Abstract Investigations have been carried out to determine the deformation modes and load-compression characteristics of tapered, thin-walled truncated frusta and tubes of square cross-section of rigid polyvinychloride (PVC). The latter were fabricated from sheet material and bent and seam welded; they constitute potential absorbers of energy. A theoretical model for predicting the mean loads in the plastic post-buckling range is developed on the basis of an inextensional folding mechanism and the notion of stationary and travelling plastic hinges. The analytical results are compared with experimental ones and show good agreement.

Experimental investigation into the axial plastic collapse of steel thin-walled grooved tubes

Abstract Experimental investigations were conducted into the quasi-static collapse and energy absorption characteristics of thin-walled steel tubes containing a number of geometrical discontinuities in the form of grooves of constant depth and axial length. The failure modes and load-deflection characteristics are discussed and compared with the corresponding theoretical values. An inextensional collapse mechanism is used to describe a non-symmetrical diamond mode shell folding which takes into account the concept of stationary circumferential and inclinded travelling hinges.

The inextensional collapse of grooved thin-walled cylinders of PVC under axial loading

Abstract An inextensional collapse mechanism is considered for the crumpling of thin-walled, grooved tubes and tubes without any discontinuities (non-grooved), when subject to axial load. Shortening of the tube (or shell) height is achieved by folding in a non-aximmetric diamond mode about stationary circumferential and inclined plastic hinges; collapse is initiated at the thinnest section of the tube (groove) and spreads along the various rings and grooves of which the tube consists, by passage as a travelling hinge. Expressions for the mean collapse load when the shell material is rigid-perfectly plastic are developed. Predicted loads based on the collapse modes encountered, when compared with those obtained experimentally, using rigid PVC tubes of constant axial length and groove dimensions (depth and length), are found to be in good agreement.

The modelling of the progressive extensible plastic collapse of thin-wall shells

Abstract A theoretical model describing the progressive extensible plastic collapse of thin-wall conical and cylindrical shells is presented. The proposed theory enables the load-deflection curves during axial compression following the deformation history of the shell to be evaluated. The comparison of theoretical curves with experimental ones shows a fair degree of accuracy.

Deformation Characteristics of Crashworthy Thin-Walled Steel Tubes Subjected to Bending

The collapse behaviour and crashworthy characteristics of cantilever circular tubes subjected to bending are studied both theoretically and experimentally. Three different fixture devices were used and their effect on failure behaviour of the tube was investigated in detail. A theoretical method, proposed by Hodge, slightly modified, is used to analyse the elastic and elastoplastic phases of bending, while a rigid-perfectly plastic analysis is developed to describe the plastic bending phase. Agreement between experimental and theoretical results was found to be quite good.