Buckling and wrinkling of anisotropic sandwich plates (original) (raw)
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Davies and Hakmi (1990) [5] studied the local buckling behaviour of a compressed plate element supported by relatively weak isotropic core medium. When the sandwich panel is subjected to uniform compression the authors represented the panel as a simply supported plate resting on half space linear elastic foundation. The critical buckling stress was determined using the principle of minimum strain energy method following Timoshenko and Gere‟s method (1961). For simply supported plates without foundation they added the strain energy contribution for the core assuming it to be the elastic foundation with exponentially decaying displacement. Parameter representing the decay in the displacement of the core was found by minimizing the strain energy. This leads to a formula for the buckling coefficient of sandwich pane which is used to achieve the ultimate strength of plate using the effective width concept (i.e.Winter formula). The authors found that the results did not quite agree with the experimental results. Improved correlation was obtained by arbitrarily reducing the value of an intermediate parameter. Davies and Hakmi (1991) [6] reviewed the analytical methods for the evaluation of buckling stress of sandwich panels for plane and profiled faces. They developed analytical formula for wrinkling stress based on considering the core as an elastic half space, by treating the width of the plate as wider flat face (i.e. width of the plate increases to infinity), this formula is modified for lightly profiled faces by introducing the effect of flexural rigidity of profiled face. Also the authors introduced practical design reduction factors for both cases due to imperfection and material non-linearity. For the profiled sandwich panels authors adopted design formula similar to Winter formula based on experimental mean values and numerical post-buckling analysis.The sandwich panels, one of the attractive engineering structures mixed between two different materials to achieve high ultimate strength associated with light weight structures. Usually, the sandwich panels comprise of foam core and thinner high strength steel faces. This report discusses currently design formulae of local buckling behaviour of sandwich panels with profiled faces using finite element method. Multiple wave finite element models adopted to investigate and examine the adequacy of currently approach for design. This report presents the details of examining the FEA model including geometry, dimensions, load pattern and boundary conditions. The FEA model gives well agreement using experimental programme of Pokharel and Mahendran (2003). However, it appears the currently design formulae are conservative for the plate elements with low b/t ratios while over conservative for high b/t ratios (slenderness plate). A unified design formula of local buckling behaviour is developed.
Some improvements to the design of sandwich panels subject to local buckling effects
Past research into the local buckling behaviour of fully profiled sandwich panels has been based on polyurethane foams and lower grade steels, and not for very slender plates. The Australian sandwich panels use polystyrene foam and thinner (0.42 mm) and high strength steels (G550 with a minimum yield stress of 550 MPa), which are bonded together using separate adhesives. Therefore a research project on Australian sandwich panels was undertaken using experimental and finite element analyses. The experimental study on 50 foam-supported plate elements and associated finite element analyses produced a large database for sandwich panels subject to local buckling effects, but revealed the inadequacy of conventional effective width formulae for panels with slender plates. It confirmed that these design rules could not be extended to the slender plates in their present form. In this research, experimental and analytical results were used to improve the design rules. This paper presents the details of experimental and finite element analyses, their results and the improved design rules.
Past research in Europe and the USA (Davies, Hakmi 1987, 1990, 1992, 1993, Hassinen 1995, ECCS,2000) has investigated the local buckling behaviour and developed modified conventional effective width rules for the plate elements in sandwich panels. However, these studies have been based on polyurethane foams and lower grade steels, and rely on some empirical factors. Moreover, these rules can be applied only for low width to thickness (bit) ratios (Figure 2) of the plate elements. But in the sandwich panel construction, bit ratios can be as large as 600 (Mahendran and Jeevaharan, 1999). Therefore a research project was conducted using a series of experiments and numerical analyses to study the local buckling behaviour of sandwich panels made of high strength steel faces and polystyrene foam covering a wide range of bit ratios. The Australian sandwich panels use polystyrene foam and thinner (0.42 mm) and high strength steels (G550 with a minimum yield stress of 550 MPa), which are bonded together using separate adhesives. Therefore a research project on Australian sandwich panels was undertaken using experimental and finite element analyses. The experimental study on 50 foam-supported plate elements and associated finite element analyses produced a large database for sandwich panels subject to local buckling effects, but revealed the inadequacy of conventional effective width formulae for panels with slender plates. It confirmed that these design rules could not be extended to the slender plates in their present form. In this research, experimental and analytical results were used to improve the design rules. This paper presents the details of experimental and finite element analyses, their results and the improved design rules.
Finite Element Analysis and Design of Sandwich Panels Subject to Local Buckling Effects
Past research into the local buckling behaviour of fully profiled sandwich panels has been based on polyurethane foams and thicker lower grade steels. The Australian sandwich panels use polystyrene foam and thinner and high strength steels, which are bonded together using separate adhesives. Therefore a research project on Australian sandwich panels was undertaken using experimental and finite element analyses. The experimental study on 50 foam-supported steel plate elements and associated finite element analyses produced a large database for sandwich panels subject to local buckling effects, but revealed the inadequacy of conventional effective width formulae for panels with slender plates. It confirmed that these design rules could not be extended to slender plates in their present form. In this research, experimental and numerical results were used to improve the design rules. This paper presents the details of experimental and finite element analyses, their results and the improved design rules.
On the elastic stability of simply supported anisotropic sandwich panels
Composite Structures, 2007
Here, the elastic stability behavior of simply supported anisotropic sandwich flat panels subjected to mechanical in-plane loads is investigated using an analytical approach. The formulation is based on first-order shear deformation theory and the shear correction factors employed are based on energy consideration that depends on the lay-up as well as material properties. The governing equations are obtained using the Raleigh-Ritz method assuming a combination of sine and cosine functions in the form of double Fourier series for the displacement fields. The effectiveness of the integrated formulation is tested for global characteristics considering examples related to multi-layered laminates and sandwich panels for which solutions are available.
Theoretical and experimental analysis of asymmetric sandwich structures
Composite Structures, 2002
A new technology known as asymmetric sandwich structures is now used for the design of lightweight structures. Static failure tests demonstrate the high performance of this technology and show its original mechanical behavior. Due to this complex mechanical behavior, the use of non-linear finite element models in the pre-project phase is a long, expensive process. This paper presents a specific theory which enables faster design loops. The theory is first validated by comparison to numerical models and is then used to correlate structural tests on asymmetric sandwich plate under combined compression/shear loadings. The tests were conducted on original test equipment designed to investigate the capabilities of this technology. Ó
Buckling analysis of members restrained by sandwich panels
Rakenteiden Mekaniikka, 2021
An analytic method is presented for the analysis of flexural restraint of members by sandwich panels. Using the method, which is based on the solutions of the fourth order differential equations, the restraint effect of sandwich panels can be approximated in practical cases. The reliability of the method is shown based on tests and finite element analyses. New results are shown using the analytic method for buckling cases and for P-δ analysis in the elastic range. The exact finite element method (FEM) formulation is given for more complicated cases.
On global and local buckling response of structural angle sandwich panels
Thin-Walled Structures, 2022
Having in mind the topic of industrialised construction and the benefits of modular construction, sandwich panels are investigated to be utilised as load-bearing wall elements. To assess its full potential, the present paper tackles the linear elastic buckling response of axially loaded angle sandwich panels, by means of numerical and analytical calculations, as the upper bound of its load bearing capacity. The failures modes are obtained and framed for concentrically loaded angle panels with fixed and pin-ended supports. A parametric study of the angle panel comprising a series of finite element models is undertaken where responses are compared with analytical calculations based on the theory of sandwich panels. Boundaries for local and global buckling are identified and framed.
An engineering vision about composite sandwich structures analysis
Journal of The Brazilian Society of Mechanical Sciences and Engineering, 2018
As shown in the literature, there is plentiful information about sandwich panels. Two of the most common points under discussion are the failure modes and the efficiency of numerical simulations considering the stiffness and interlaminar stress. The failure modes in the literature are not always likely to happen in practice, and representing them becomes a challenging task. Regarding the numerical simulations, new assumptions and formulations appear in order to consider the shear stress in the honeycomb CORE and to minimize processing time in 3D models. Although new mathematical solutions emerge, in some cases they are unpractical for engineering applications and must be evaluated and compared with test results in order to verify their consistency. Therefore, experimental results are necessary to validate theories to comply with the failure modes observed in sandwich panels and to validate the finite element model. Also, the main focus of the literature is on the theoretical formulation and not in engineering applications. In this sense, the main contribution of this paper is to bring forward experimental results of aeronautical sandwich panels whose data are scarce and therefore contributes to the validation of new developments. In addition, the purpose of this work contributes to the use of the finite element models with composite sandwich panels where the appropriate input for 2D (plate) and 3D (solid) elements is unclear. It should be pointed out that for failure investigation the first step is validating the finite element model. In this sense, a typical aircraft panel with experimental results is presented. The finite element model and the input parameters that are not mentioned in the classical literature are also presented. The experimental strain from specimen tested agreed well with the numerical simulations results.