Bending of curved sandwich beams, a numerical approach

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.

Section: Introductionmentioning

confidence: 57%

High Order Analysis of Junction Between Straight and Curved Sandwich Panels

Lyckegaard¹,

Thomsen

2004

“…The failure occurred by fracture of the core near the outer F/C interface. Stress analysis of curved monolithic and sandwich beams [1,3,5,6] loaded by opening bending moments reveals that the curved region will be subject to a radial tension ( r > 0). Sandwich beams with a weak foam core are prone to fail due to through-thickness tension in the core, or at the F/C interface if this is the weak link.…”

Section: Flexure Test Resultsmentioning

confidence: 99%

Flexural Strength of Curved Sandwich Beams with Face/Core Debond

Layne

Carlsson

2002

The influence of a face/core (F/C) debond on the flexural stiffness and strength of curved sandwich beams under opening bending moments has been experimentally examined. The sandwich beams consisted of glass/polyester face sheets over a PVC foam core. Debonds of various sizes were defined by inserting thin non-stick Teflon films at the outer F/C interface in the curved region of the beam prior to processing. The beams were tested in flexure in a specially designed fourpoint bend test fixture. The load versus displacement and surface strains at the apex of the beam were recorded to examine the response. It was observed that the debonded face sheet lifted off of the core and underwent a bifurcation associated with strain reversal. Beam failure occurred by propagation of the debond. It was observed that the beams suffered marginal reductions in stiffness, but substantial reductions in strength due to the presence of a debond. Linear finite element analysis was performed to examine the initial response of the beams.

“…The kinematic relations for the face-sheets are based on small deformation assumptions and neglect of the shear deformations of the faces. In the upper face the kinematic relations are (6) (7) where z t is measured from the centerline of the upper face downward and ε ot , χ t are the inplane strain and the curvature of the upper face. The kinematic relations for the lower curved face are (8) High-Order Analysis of Sandwich Panels with Flat and Generally Curved Faces (…”

Section: Mathematical Formulationmentioning

confidence: 99%

“…Theoretical and numerical models for the analysis of curved panels have been developed by many researchers. Among these one can list Smidt [6,7], Bozhevolnaya and Skvortsov and Skvortsov et al [8][9][10], Rossettos [11], Singh [12], Noor et al [13] and Librescu et al and Hause et al [14][15][16]. These models, as well as many others, focus on curved panels where the upper and lower faces are parallel, thus the height of the core is kept uniform throughout the entire panel and the core is incompressible.…”

Section: Introductionmentioning

confidence: 99%

High-Order Analysis of Unidirectional Sandwich Panels with Flat and Generally Curved Faces and a “Soft” Core

Rabinovitch

Frostig

2001

The bending behavior of a unidirectional sandwich panel with flat and generally curved faces and a flexible core in the vertical direction is investigated. The studied panels consist of an upper flat face sheet, a core of variable thickness, and a lower face sheet that can take any geometrical layout described by an analytical function. The core is assumed a two-dimensional elastic medium with shear and transverse vertical rigidities only, and the face sheets are considered as membrane and bending members made of metallic or composite materials. The term unidirectional refers here either to a beam (narrow panel) or to a wide beam (panel) undergoing a cylindrical bending. The field equations and the boundary conditions are derived via the variational principle of the virtual work and transformed from the local polar coordinate system of the curved face into the global Cartesian one. Higher order effects due to flexibility of the core in the form of nonlinear deformation fields are incorporated in the proposed analysis as a result of the closed-form solution of the field equations and are not postulated a priori. Numerical results in terms of deformations, stresses, and stress resultants are presented for some typical cases of flat-curved panels. The effect of a wide range of layouts, various boundary conditions, and the influence of manufacturing imperfections in the form of initially wrinkled face are investigated. The results demonstrate the capabilities and generality of the proposed model and present its ability to predict the high-order localized effects that characterize such panels.