Anders Lyckegaard

Parametric study of structurally graded core junctions

In practical sandwich constructions it is often necessary to reinforce the core with high strength inserts to facilitate concentrated loads. The junction between the main core and the core insert is a potential weak spot of the sandwich structure. This section of the sandwich structure is investigated using finite element analysis and the results are compared with experimental data. Furthermore, parameters concerning the shape of the core junction are investigated using finite element analysis.

High Order Analysis of Junction Between Straight and Curved Sandwich Panels

When curved and straight sandwich panels are joined, localized bending effects arise in the vicinity of the curvature discontinuity. To investigate this the problem is analyzed using a high order sandwich beam theory. This, however, is not straight forward because the continuity conditions at a junction cannot be fulfilled in an exact sense. Instead an averaging scheme is suggested and used to obtain a set of approximate continuity conditions. The accuracy of these approximate continuity conditions is estimated and a numerical example is conducted and compared with finite element analyses. The results prove to be within the estimates of the inaccuracy. A parametric study is conducted to identify possible ways to reduce the localized bending effects.

Sandwich Beam with a Periodical and Graded Core Manufactured Using Rapid Prototyping

This article presents a technique for the production of graded sandwich cores, and a study of the effect of lengthwise grading of core properties for the facilitation of transverse loading. A significant failure mode of sandwich panels is caused by indentation of the foam core in regions at which local forces are introduced into the sandwich panel. The aim of this work is to synthesize a microstructure that can diminish this failure mode. By applying a rapid prototyping technique a periodic, open beam structure is synthesized. Additionally, the structure has been graded in the longitudinal direction by alternating over the beam diameter. The structure obtained is joined to aluminium face sheets to form a sandwich beam. The panel has been subjected to a three point bending test and the results have been compared to a finite element model, and further indentation tests show an increased transverse stiffness in the strengthened part of the beam.

On Lateral Buckling failure of Armour Wires in Flexible Pipes

This paper introduces the concept of lateral buckling of tensile armour wires in flexible pipes as a failure mode. This phenomenon is governed by large deflections and is therefore highly non-linear. A model for prediction of the wire equilibrium state within the pipe wall based on force equilibrium in curved beams and curvature expressions derived from differential geometry is presented. On this basis, a model of the global equilibrium state of the armour layers in flexible pipes is proposed. Furthermore, it is demonstrated how this model can be used for lateral buckling prediction. Obtained results are compared with experiments.Copyright

Asymptotic Analysis for the Curved/Straight Sandwich Panel Junctions

Cylindrical bending of a sandwich panel assembly consisting of straight and curved sections is considered. The sandwich assembly is statically determinate, loaded by a uniform pressure and possibly by forces and moments at its edges. The influence of the change of geometry upon the stresses and displacements at the transition zone between the different panel sections is investigated. An exact asymptotic mathematical model based on a number of small parameters is derived. The model assumes the faces of the sandwich panels to be thin elastic beams obeying the Kirchhoff-Love assumptions, while the isotropic core is treated as a 2-D elastic medium. An asymptotic expansion technique is exploited to derive analytical estimate formulae for calculating the deformation and stress distribution characteristics at the critical sections of the assembly. A numerical example illustrates the applicability of the derived formulae, and the validity of the proposed approach is demonstrated through comparison with FEM calculations.

Stress Analysis and Prediction of Failure in Structurally Graded Sandwich Panels

Structural sandwich panels can be considered as a special type of composite laminate where thick, lightweight and compliant core material separates two thin, stiff and strong face sheets. Sandwich panels transfer bending and shearing load very effectively, but at the same time they offer limited resistance towards application of transverse loads, see e.g. Zenkert [1] or Allen [2]. A commonly used method of overcoming the problems associated with concentrated transverse loading is to introduce core inserts of higher strength and stiffness. This usually solves the problem of local reinforcement, but it also introduces new interfaces between materials of very different elastic properties.

Local Effects Induced by Core Junctions in Sandwich Beams under General Loading Conditions

Local effects occurring near junctions between different cores in sandwich structures subjected to axial and transverse forces and bending moments are considered. These local effects are associated with large stress concentrations in the faces and the core near the core junctions. The local effects are studied for two typical cases representing industrial applications. Finite element analyses show that significant stress concentrations are induced near core junctions subjected to transverse, tension/compression as well as bending loads. Finally, improved designs of core junctions are discussed.

Study of Fatigue Endurance of Conventional and Modified Core Junctions in Sandwich Beams

Local effects occurring near junctions between different cores in sandwich structures are considered. Two groups of sandwich beams with conventional butt and reinforced butt core junctions, respectively, were examined experimentally in three-point bending under static and fatigue loadings. A rigorous statistical treatment of the obtained data has shown unambiguously that sandwich beams with modified, that is reinforced, butt junctions display superior structural performance compared with sandwich beams with the traditional core junctions.

Sandwich panel with a periodical and graded core

This paper presents a technique for the production of graded sandwich cores. A significant failure mode of sandwich panels is the indentation of the foam core in regions at which local forces are introduced into the sandwich panel. The aim of this work is to synthesise a microstructure that can diminish this failure mode. By applying a rapid prototyping technique a periodic, open beam structure has been synthesised. Additionally the structure has been graded in the longitudinal direction by alternating over the beam diameter. The obtained structure was joined with aluminium face sheets to form a sandwich beam. The panel was subjected to a three point bending test and the results were compared to a finite element model.