Classification of Thin-Walled Conical Vessels for Design Against Axisymmetric Plastic Collapse Under External Pressure

This paper presents the results of a study that investigates the propensity of thin walled vessels with cone-cylinder junctions to plastically collapse under external pressure. The investigation focuses on the conical portion of the vessel collapsing in an axisymmetric mode prior to buckling in a classical lobar mode. Using a parametric study, comparison is made between the factor of safety afforded by design-by-rule approaches such as that offered in ASME Section VIII Div. 1, ASME Section VIII Div. 2 Part 4.4 and elastic-plastic design by analysis approaches prescribed by ASME Section VIII Div.2 Part 5. Further, the results of the parametric study are used to determine the key parameters that result in the occurrence of an axisymmetric collapse mode before the classical lobar buckling mode. The research has led to the development of a set of criteria to indicate susceptibility of geometry to axisymmetric collapse prior to classical lobar buckling.

Analytical Model Study of Ellipse Crank Arm Final Upset Forging Force on Slab Method

According to the structure of the crank arm, the conformal mapping method was adopted to transform the elliptical section map of it to the round. Then by the slab method an analytical model for final upsetting force of the crank arm was established, which is a derivation based on assumptions of axisymmetric plastic forming status. Finally, a simulation was implemented in case of the second crank of crankshaft 6G32. Accordance to it the accuracy of the analytical model was examined. Further more the causes of the data deviation from the model and the simulation were analyzed in this thesis.

New insights into the collapsing of cylindrical thin-walled tubes under axial impact load

The current paper presents further investigations into the crushing behaviour of circular aluminium tubes subjected to axial impact load. Experiments prove that in order to achieve the real collapsing shape of tubes under axial loads in numerical simulations, an initial geometric imperfection corresponding to the plastic buckling modes should be introduced on the tube geometry before the impact event. In this study, it is shown that the collapsing shape of tube is affected by this initial imperfection and consequently it is shown that by applying an initial geometric imperfection similar to the axisymmetric plastic buckling mode, the tubes tend to collapse in a concertina mode. This phenomenon is studied for circular tubes subjected to axial impact load and two design methods are suggested to activate the axisymmetric plastic buckling mode, using an initial circumferential edge groove and using one- and two-rigid rings on the tube. In each case the broadening of the concertina collapsing region is estimated using numerical simulations. Experimental tests are performed to study the influence of cutting the edge groove on the collapsing mode. In order to optimize the crashworthiness parameters of the structure such as the absorbed energy, maximum deflection in axial direction, maximum reaction force, and mean reaction force, a system of neural networks is designed to reproduce the crushing behaviour of the structure, which is often non-smooth and highly non-linear in terms of the design variables (diameter, thickness, and length of tube). The finite-element code ABAQUS/Explicit is used to generate the training and test sets for the neural networks. The response surface of each objective function (crashworthiness parameters) against the change of design variables is calculated and both single-objective and multi-objective optimizations are carried out using the genetic algorithm.

COLLAPSE OF CORRUGATED CIRCULAR CYLINDERS UNDER UNIFORM EXTERNAL PRESSURE

The paper describes a finite element investigation into the buckling, under uniform external pressure, of four submarine pressure hulls. Two of these hulls were traditional ring-stiffened types, but two of these hulls were in the form of corrugated circular cylinders. The latter design was based on an invention by the present author. The investigation found that the new design was structurally efficient and in the case of the smaller vessel, it was found to be structurally more efficient than the conventional design. Another investigation, based on axisymmetric plastic buckling, was conducted on the two corrugated vessels, to determine if they were prone to collapse through the bellows' mode of failure. This investigation was carried out because former critics of this work stated that the corrugated circular cylinders would fail by the bellows' mode of failure. Neither of the two corrugated pressure hulls was found to fail through the bellows' mode of failure, thereby completely vindicating the present author. The author, however, concludes that the bellows' mode of failure can occur if the cone angles were too large. Two of the finite element theories were based on the author's work, but the giant computer package ANSYS was also used to study non-symmetric bifurcation buckling. This work was carried out to vindicate the author's in-house computer programs, which were simpler to use than ANSYS.

Residual Stress of Thin-Wall Pipe Subjected to Axisymmetric Plastic Expansion

A straight pipe was expanded at one end by inserting a rigid disk. The residual stress measured at the inner surface shows a strong tensile peak beyond the region where the pipe was directly expanded by the insertion of the disk. The reason the residual stress reaches its peak at a location further into the pipe is discussed based on a FE analysis. The residual stress was found to reach its tensile peak at the plastic region front that was developed during the pipe expansion. A simple formula for identifying the tensile peak location is also proposed.