Theoretical and experimental analysis of asymmetric sandwich structures (original) (raw)

Combined shear/compression structural testing of asymmetric sandwich structures

Experimental Mechanics, 2004

Asymmetric sandwich technology can be applied in the design of lightweight, non-pressurized aeronautical structures such as those of helicopters. A test rig of asymmetric sandwich structures subjected to compression/shear loads was designed, validated, and set up. It conforms to the standard certification procedure for composite aeronautical structures set out in the "test pyramid", a multiscale approach. The static tests until failure showed asymmetric sandwich structures to be extremely resistant, which, in the case of the tested specimen shape, were characterized by the absence of buckling and failure compressive strains up to 10,000 ยต strains. Specimens impacted with perforation damage were also tested, enabling the original phenomenon of crack propagation to be observed step-by-step. The results of the completed tests thus enable the concept to be validated, and justify the possibility of creating a much larger machine to overcome the drawbacks linked to the use of small specimens.

Effects of manufacturing procedure on unsymmetrical sandwich structures under static load conditions

Materials and Design, 2012

In recent years sandwich structures have been widely used in marine industry; such reason has lead to the study of mechanical properties of the above mentioned structures through the evaluation of the effects induced by different technological procedures. Therefore, this work presents unsymmetrical sandwich structures realised using both lay up and vacuum bag technology. In order to find a static characterisation of the sandwich structure, firstly flatwise and edgewise compressive tests were performed. Afterwards, a three point flexural test was realised in order to examine the different effects of a load, which has been applied to either one or the other side of an unsymmetrical sandwich structure. Thanks to the above mentioned tests, it has been possible to find out and interpret a number of fracture mechanisms that take place when the load conditions change and/or when the technological procedure used to produce the samples varies. Moreover, a theoretical model capable of predicting the stresses inside the sandwich sample is proposed.

FINITE ELEMENT ANALYSIS OF SANDWICH STRUCTURES WITH A FUNCTIONALLY GRADED CORE

Sandwich structures, broadly utilized in aviation and maritime applications, will in general be restricted to a little scope of material mixes. Practically evaluated materials (FGMs) have properties that shift slowly with area inside the material. For instance, a rocket engine packaging can be made with a material framework to such an extent that within is made of an unmanageable material, the outside is made of a solid metal, and the change from the hard-headed material to the metal is progressive through the thickness. In this proposal, limited component investigation is performed on a sandwich structure with a practically evaluated center for dissecting its solidarity. Numerical connections are done to decide the material properties of practically reviewed material with metal Steel utilizing Ceramic as interface zone for each layer up to 10 layers. FGM's are considered for volume parts of K=2. The sandwich structure material is steel. 3D demonstrating is done in Creo 5.0. Static, Modal and Random Vibration examination are done the ordinary sandwich design and sandwich structure with a practically reviewed center utilizing limited component investigation programming ANSYS 19. The outcomes are looked at for both the models. A sandwich structure comprises of two flimsy, solid, and solid face sheets associated by a thick, light and low-modulus center utilizing glue joints to acquire productive lightweight construction (Zenkert, 1997; Vinson, 2001). In the vast majority of the cases the faces convey the stacking, both in-plane and bowing, while the center opposes cross over shear loads. A sandwich works similarly as an I-shaft with the distinction that the center of a sandwich is of an alternate material and is loosened up as a consistent help for the face sheets. The fundamental favorable position of a sandwich structure is its incredibly high flexural solidness to-weight proportion contrasted with different designs. As an outcome, sandwich development brings about lower horizontal distortions, higher clasping obstruction, and higher characteristic frequencies than do different designs. Accordingly, for a given arrangement of mechanical and natural burdens, sandwich development frequently brings about a lower underlying load than do different setups. Not many of the downsides of sandwich structures are: producing techniques, quality control and joining challenges. 1.1 Sandwich Theory Sandwich hypothesis depicts the conduct of a bar, plate, or shell which comprises of three layers-two face sheets and one center. The most normally utilized Sandwich structures, generally utilized in aviation and maritime applications; will in general be restricted to a little reach 1. INTRODUCTION

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.

Structural behavior of sandwich panels with asymmetrical boundary conditions

Journal of Constructional Steel Research, 2015

Asymmetrically supported and loaded sandwich panels with a polyurethane soft core and isotropic or orthotropic steel faces were analyzed in laboratory tests and numerical simulations. The influence of the steel face microprofilation on the mechanical and kinematical responses of the sandwich panel is considered in the paper. The real experiments were conducted for two supporting systems. For each supporting system isotropic and orthotropic sandwich faces were taken into account. The numerical simulations, in which 2D composite shell elements were used, correspond to the real experiments. The laboratory tests showed that introducing the orthotropic face layer significantly increases the load capacity of the sandwich panel. In the case of asymmetrically supported systems effective flexural rigidity increases too. The paper demonstrates that a relatively simple FE model can be successfully used to assess the global behavior of sandwich panels in complex boundary conditions. Satisfactory consistency of the numerical and real results in the linear range of structural behavior was obtained. Further improvement of the model is possible by introducing a definition of the failure criteria.

Experimental and numerical evaluation of sandwich composite structures

Composites Science and Technology, 2004

The main problem working with sandwich composite structures is their intrinsic anisotropy and non-homogeneity that does not allow their correct modelling. Nowadays the available data on mechanical properties of complex structures, necessary to allow a correct and reliable design, are not sufficient. The aim of the present work is to extend the knowledge of mechanical properties both on single components and on complete structures, focusing on the effects induced by different kind of skin arrangements (Kevlar, glass and carbon fibres). Compressive, shear and flexural tests were performed for a complete static mechanical characterisation of the sandwich structure both on each single component and on the complex structures in order to acquire important comparison parameters. The mechanical results of each component were used as input data in order to implement the FEM analysis by the commercial ANSYS code. A simplified model is proposed to simulate the compressive and flexural tests of a glass fibre sandwich structure. In addition their mechanical behaviour has been compared with experimental data by the aforesaid static tests of complex sandwich structures.

A new hybrid concept for sandwich structures

Composite Structures, 2008

Sandwich structures are considered as optimal designs for carrying bending loads and can be either metal (aluminium faces and honeycomb or metal foam cores) or polymer structures (composite faces with polymer foam cores). In this paper, a new hybrid sandwich structure has been developed by combining most of the advantages of metallic and polymeric materials while avoiding some of their main disadvantages. For this new concept metal sheets are used at the outer surfaces to maximize rigidity while introducing in between lightweight cores adhesively bonded to keep the whole structure together. Furthermore, composite or wood layers may be used as intermediate layers to improve impact resistance. Potential methods for the manufacturing of this new structure are based on compression under vacuum. The results include the study of several panel configurations theoretically based on Finite element analysis and on the modified simplified equations and experimental results in the most representative cases of the study.

Design and Testing of Sandwich Structures with Different Core Materials

Materials Science, 2012

The purpose of this study was to design a lightweight sandwich panel for trailers. Strength calculations and selection of different materials were carried out in order to find a new solution for this specific application. The sandwich materials were fabricated using vacuum infusion technology. The different types of sandwich composite panels were tested in 4-point bending conditions according to ASTM C393/C393M. Virtual testing was performed by use of ANSYS software to simplify the core material selection process and to design the layers. 2D Finite element analysis (FEA) of 4-point bending was made with ANSYS APDL (Classic) software. Data for the FEA was obtained from the tensile tests of glass fiber plastic (GFRP) laminates. Virtual 2D results were compared with real 4-point bending tests. 3D FEA was applied to virtually test the selected sandwich structure in real working conditions. Based on FEA results the Pareto optimality concept has been applied and optimal solutions determined.