Guoxing Lu

On the axial splitting and curling of circular metal tubes

Abstract The present paper investigates the axial splitting and curling behaviour of circular metal tubes. Mild steel and aluminum circular tubes were pressed axially onto a series of conical dies each with different semi-angle. By pre-cutting eight 5 mm slits which were distributed evenly at the lower end of each tube, the tube split axially and the strips curled outward. Experiments showed that this mechanism results in a long stroke and a steady load. An approximate analysis is presented which successfully predicts the number of propagated cracks, the curling radius and the force applied. This analysis takes into account ductile tearing of the cracks, plastic bending/stretching and friction. Effects of tube dimensions, semi-angle of the die and friction are discussed in detail.

Energy absorption in splitting square metal tubes

This paper presents an investigation into the energy absorbing behaviour of axially splitting square metal tubes. Tubes 50 mm square with a variable thickness were pushed slowly against rigid pyramid shaped dies, which had various semi-angles. By pre-cutting 5 mm long slits at the four corners, the tube splits along the corners and curls outward with a certain radius at a constant force. In this energy dissipating system, there are three components: tearing energy, plastic deformation energy and frictional energy. Theoretical analysis of the three energy components is presented. Curl radius is also studied in detail. Good agreement between experiments and theory is obtained. The results show that tubes which both split and curl may be used as efficient, long stroke energy absorbing devices.

A study of the plastic buckling of axially compressed cylindrical shells with a thick-shell theory

A thick shell theory is used to calculate the critical load of plastic buckling of axially compressed cylindrical shells. The buckling equations are derived with the principle of virtual work on the basis of a transverse shear deformable displacement field. The deformation theory of plasticity is used for constitutive equations. To fit the uniaxial stress–strain curve, the Ramberg–Osgood equation is used. In the numerical examples special attention is paid to the dependence of the buckling mode on the ratios of radius to thickness R/h and length to radius L/R. This dependence divides the (R/h,L/R)-plane into simply connected regions each of which corresponds to a buckling mode. These regions form a “buckling mode map”.

On the quasi-static piercing of square metal tubes

Abstract This paper investigates the energy absorption properties of square tubes pierced by pointed punches under quasi-static conditions. In a series of tests, square section pyramidal punches and conically headed cylindrical punches were pierced slowly into square steel tubes having 40×40 mm 2 outside dimensions. Wall thicknesses of 1.6 and 2.5 mm were tested, and the length of tubes was varied. Some typical loads were plotted against deflection, and a number of interesting conclusions were drawn from the tests. Based on the test results and observations, preliminary theoretical considerations are presented. The theoretical results agree fairly with the experiments.

Comparative Research on the Crushing Behaviour of Aluminium Sheet Wrapped Square Carbon Fibre Reinforced Plastic (CFRP) Tubes

In this study, hollow square carbon fibre reinforced plastic (CFRP) tubes and aluminium sheet wrapped CFRP tubes have been axially crushed at a quasi-static loading velocity of 0.05 mm/s. A specially designed and manufactured platen with four cutting blades was used to cut and crush these two tubular structures. The four cutting blades had height of 5 mm and width of 3 mm with round tip to reduce the initial peak force and achieve a stable crushing deformation mode. Notches at one end of each tube were utilized to control the location of initial failure. The crashworthiness characteristics of hollow CFRP tubes and aluminium sheet wrapped CFRP tubes with notches that crushed by the platen with cutting blades were compared with those of tubes that crushed by a flat platen. Experimental results showed that using the platen with blades to crush the specimens with notches exhibited more stable deformation mode than the specimens without notches. Mean crushing force, energy absorption and specific energy absorption (SEA) increased when CFRP was wrapped with aluminium sheet and crushed by the platen with blades. The increase of average value of mean crushing force, energy absorption and specific energy absorption of aluminium sheet wrapped CFRP tube and crushed by the platen with blades are 16.5%, 17.3% and 5% respectively more than those for hollow tubes that crushed by a flat platen.

A theoretical model for axial splitting and curling of circular metal tubes

The paper proposes a theoretical model for circular metal tubes axially split and curled with a radius or conical rigid die. Three energy mechanisms are involved: plastic bending energy, tearing energy and frictional work in this type of energy absorbers. The crack number, curl radius and force applied are reasonably predicted by this theoretical model.

Mechanical Properties of the 2D Re-entrant Honeycomb Made via Direct Metal Printing

Auxetic structural materials show distinctive properties by exhibiting a negative Poissons ratio (NPR). When these structures are subjected to uniaxial loading, they expand in tension and contract in compression in both loading and lateral directions. In this paper, two AlSi12 re-entrant honeycomb samples were manufactured using direct metal printing (DMP). Quasi-static uniaxial tension was executed in both X and Y direction. A Digital VIC-2D Image Correlation System was used to record the deformation history. Force and displacement were measured by ZWICK machine. The results show that loading direction has a significant effect on the mechanical properties and auxeticity of the tested structure. Re-entrant honeycomb under X-loading withstand lower force and has smaller magnitude of Poissons ratio compared with that under Y-loading.

Dynamic torsional buckling of an embedded double-walled carbon nanotube

An elastic double-shell model based on continuum mechanics is presented to study the dynamic torsional buckling of an embedded double-walled carbon nanotube (EDWCNT). Based on the model, a condition is derived to predict the buckling load of the EDWCNT. It is shown that the buckling load of the EDWCNT for dynamic torsional buckling is no less than that for the static torsional buckling. Further, the effect of the van der Waals forces is discussed when an inner nanotube is inserted into an embedded outer one. In particular, the paper shows that, in the absence of the initial van der Waals forces, the buckling load of an EDWCNT is always in-between that of an isolated inner tube and of an embedded outer nanotube, which is different from the result obtained by neglecting the difference of radii. This indicates that disregarding the difference of the radii of the double-walled nanotubes can not properly describe the effect of the van der Waals forces between interlayer spacing.

Dynamic response of monolithic and sandwich structures subjected to impulsive and impact loadings

Monolithic and sandwich structures have been widely used as energy absorption structures in military and civil engineering. This article reviews theoretical analyses of monolithic beams and plates subjected to static loading, impulsive loading and impact by a mass systematically. Experimental data collected from the literatures are compared with these theoretical results. In addition, the critical impulses for the failure of the monolithic structures are also reviewed. Furthermore, sandwich structures under quasi-static, low-velocity impact, high-velocity impact and blast loading, as well as their failure modes, are also summarized. The research methodology involves experimental investigations, theoretical analyses and numerical simulations.

Cutting Deformation Mechanisms of Square Aluminium/CFRP Tubes

The aim of this study is to find the best platen with blades as a new energy dissipating mechanism that causes considerably damage to CFRP/aluminium tubes. Specially designed and manufactured platens with five different cutting blade profiles were used to simultaneously cut and crush square CFRP tubes and aluminium sheet-wrapped CFRP tubes. The platens with blades were evaluated in terms of the deformation mode, mean crushing force, energy absorption and specific energy absorption of tubes. Experimental results showed that tubes cut and crushed by the platen with 45o inclined blades had the best crushing performance and exhibited a more stable deformation mode compared with those for tubes cut and crushed by other platens with different blade profiles. The platens with blades acted as trigger mechanisms that minimise the initial peak crushing force and maximise the energy absorption of tubes compared with tubes crushed by flat loading platens.