A review on Static Three Point Bending Load on Composite Sandwich Panel

Transcription

1 A review on Static Three Point Bending Load on Composite Sandwich Panel Nitin Gir 1, prof.a.z Patel 2, prof.a.b Ghalke 3 ABSTRACT The use of sandwich structure continues to increase rapidly due to the wide fields of their application, for instance: satellites, aircraft, ships, automobiles, rail cars, wind energy systems, and bridge construction to mention only a few. The sandwich composites are multi-layered materials made by bonding stiff, high strength skins facings to low density core material. The main benefits of using the sandwich concept in structural components are the high stiffness and low weight ratios. In this paper static behavior of honeycomb sandwich composites are investigated through three-point bending. Keywords: Composites, honeycomb panel, three point bending, Glass fiber 1. INTRODUCTION 1.Sandwich construction is of particular interest and widely used in many structures, because the concept is very suitable for lightweight structures with high in- plane and flexural stiffness. Sandwich panels typically consist of two thin face sheets or skins and a lightweight thicker core. Commonly used materials for face sheets are composite laminates and metals, while cores are made of metallic and non-metallic honeycombs, cellular foams, balsa wood or trusses. The face sheets are typically bonded to the core with an adhesive, and carry most of the bending and in-plane loads. The core provides the flexural stiffness and out-of-plane shear and compressive strength. 2. Important issues in sandwich structures are the quality of the structure, the failure mechanisms that are developed under various loading conditions, effects of nonlinear material behavior and effects of geometric nonlinearities. 3. The facing skins of a sandwich panel can be compared to the flanges of an I-beam, as they carry the bending stresses to which the beam is subjected. With one facing skin in compression, the other is in tension. Similarly the honeycomb core corresponds to the web of the I-beam. The core resists the shear loads, increases the stiffness of the structure by holding the facing skins apart, and improving on the I-beam, it gives continuous support to the flanges or facing skins to produce a uniformly stiffened panel. The core-to-skin adhesive rigidly joins the sandwich components and allows them to act as one unit with a high torsion and bending rigidity. 2. LITERATURE REVIEW S. Belouettar, A. Abbadi, Z. Azari, R. Belouettar, P. Freres[1] they studied static and fatigue behaviours of honeycomb sandwich composites, made of aramide fibres and aluminium cores, are investigated through four-point bending tests. Damage and failure modes are reported and discussed. Global and local parameters were considered to evaluate the fatigue life of the analysed sandwich composites. Effects of core densities and the cell orientation (L or W) on the maximum load and on the damage processes (initiation and evolution) are also investigated. It was also found from the experimental program that the stiffness might not be a good monitoring measure for the health of a specimen. Isaac M. Daniel, Jandro L. Abot[2] The objective of this work was to determine experimentally the exural behavior of composite sandwich beams and compare the results with predictions of theoretical models. Sandwich beams were Volume 3, Issue 12, December 2015 Page 53

2 fabricated by bonding unidirectional carbon/epoxy face sheets (laminates) to aluminum honeycomb cores with an adhesive lm. All constituent materials (composite laminates, adhesive and core) were characterized independently. Special techniques were developed to prevent premature failures under the loading pins and to ensure failure in the test section. Sandwich beams were tested under four-point and three-point bending. Strains to failure in the face sheets were recorded with strain gages, and beam defections, and strains in the honeycomb core were recorded by using moireâ Techniques. The beam face sheets exhibited a softening non-linearity on the compression side and a stiffening nonlinearity on the tension side. Experimental results were in good agreement with predictions from simple models which assume the face sheets to behave like membranes, neglecting the contribution of the honeycomb core, and accounting for the non-linear behavior of the face sheets. It was found that Experimental results were in good agreement with predictions of simple models assuming the face sheets to behave like membranes and neglecting the contribution of the core, but accounting for the non- linear behavior of the face sheets. Henrik Herranen, Ott Pabut, Martin Eerme, Jüri Majak, Meelis Pohlak, Jaan Kers, Mart Saarna, Georg Allikas, Aare Aruniit[3] The purpose of their study was to design a light-weight 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. Hualin Fan, Lin Yang, Fangfang Sun, Daining Fang[4] To restrict debonding, carbon fiber reinforced lattice-core sandwich composites with compliant skins were designed and manufactured. Compression behaviors of the lattice composites and sandwich columns with different skin thicknesses were tested. Bending performances of the sandwich panels were explored by three-point bending experiments. Two typical failure mechanisms of the lattice-core sandwich structures, delaminating and local buckling were revealed by the experiments. Failure criteria were suggested and gave consistent analytical predictions. For panels with stiff skins, delamination is the dominant failure style. Cell dimensions, fracture toughness of the adhesives and the strength of the sandwich skin decide the critical load capacity of the lattice-core sandwich structure. The mono-cell buckling and the succeeding local buckling are dominant for the sandwich structures with more compliant skin sheets. Debonding is restricted within one cell in bending and two cells in compression for lattice-core sandwich panels with compliant face sheets and softer lattice cores. Jin Zhang, Peter Supernak, Simon Mueller-Alander, Chun H. Wang[5] The bending strength, stiffness and energy absorption of corrugated sandwich composite structure were investigated to explore novel designs of lightweight loadbearing structures that are capable of energy absorption in transportation vehicles. Key design parameters that were considered include fibre type, corrugation angle, core-sheet thickness, bond length between core and face-sheets, and foam inserts. The results revealed that the hybridization of glass fibres and carbon fibres (50:50) in face-sheets was able to achieve the equivalent specific bending strength as the facet-sheets made entirely of carbon fibre composites. Increasing the corrugation angle and the core sheet thickness improved the specific bending strength of the sandwich structure, while increasing the bond length led to a reduction in the specific bending strength. The hybrid composite coupons with foam insertion showed medium energy absorption, ranging between the glass fibre and the carbon fibre composite coupons, but the highest crush force efficiency among all designs. Kaveh Kabir, Tania Vodenitcharova, Mark Hoffman[6] The response of aluminium sandwich panels comprising thin foam cores and thin face sheets of low and high yield strength was investigated under three-point bending load. The effect of skin strength, bending span and core thickness on the failure modes and loads was investigated. While the lower strength face sheet is associated with lower failure loads, that decrease is not proportional to the yield strength due to the additional failure mode of face yielding. Theoretical models enabled prediction of the failure loads and elucidated the contribution of each failure mode. Failure maps were subsequently constructed which can be used for the design of foam-cored sandwich panels with very thin face sheets. Craig A. Steeves, Norman A. Fleck[7] In this Analytical predictions are made for the three-point bending collapse strength of sandwich beams with composite faces andpolymer foam cores. Failure is by the competing modes of face sheet microbuckling, plastic shear of the core, and face sheet indentation beneath the loading rollers. Particular attention is paid to the development of an indentation model for elastic faces and an elastic plastic core. Failure mechanism maps have been constructed to reveal the operative collapse mode as a function of geometry of sandwich beam, andminimum weight designs have been obtainedas a function of an appropriate structural loadind ex. It is shown that the optimal designs for composite polymer foam sandwich beams are of comparable weight to sandwich beams with metallic faces and a metallic foam core. Volume 3, Issue 12, December 2015 Page 54

3 V. Crupi, G. Epasto, E. Guglielmino[8] The use of lightweight aluminium sandwiches in the shipbuilding industry represents an attractive and interesting solution to the increasing environmental demands. The aim of this paper was the comparison of static and low-velocity impact response of two aluminium sandwich typologies: foam and honeycomb sandwiches. The parameters which influence the static and dynamic response of the investigated aluminium sandwiches and their capacity of energy absorption were analysed. Quasi static indentation tests were carried out and the effect of indenter shape has been investigated. The indentation resistance depends on the nose geometry and is strongly influenced by the cell diameter and by the skin core adhesion for the honeycomb and aluminium foam sandwich panels, respectively. The static bending tests, performed at different support span distances on sandwich panels with the same nominal size, produced various collapse modes and simplified theoretical models were applied to explain the observed collapse modes. The capacity of energy dissipation under bending loading is affected by the collapse mechanism and also by the face-core bonding and the cell size for foam and honeycomb panels, respectively. A series of low-velocity impact tests were, also, carried out and a different collapse mechanism was observed for the two typologies of aluminium sandwiches: the collapse of honeycomb sandwiches occurred for the buckling of the cells and is strongly influenced by the cell size, whereas the aluminium foam sandwiches collapsed for the foam crushing and their energy absorbing capacity depends by the foam quality. It is assumed that a metal foam has good quality if it. K.Kantha Rao, K. Jayathirtha Rao A.G.Sarwade, M.Sarath Chandra[9] Aluminum sandwich construction has been recognized as a promising concept for structural design of light weight systems such as wings of aircraft. A sandwich construction, which consists of two thin facing layers separated by a thick core, offers various advantages for design of weight critical structure. Depending on the specific mission requirements of the structures, aluminum alloys, high tensile steels, titanium or composites are used as the material of facings skins. Several core shapes and material may be utilized in the construction of sandwich among them, it has been known that the aluminum honeycomb core has excellent properties with regard to weight savings and fabrication costs. This paper is theoretically calculating Strength Analysis on Honeycomb Sandwich Panels of different materials. M.M. Venugopal, S K Maharana, K S Badarinarayan[10] The sandwich composites are multilayered materials made by bonding stiff, high strength skin facings to low density core material. The main benefits of using the sandwich concept in structural components are the high stiffness and low weight ratios. These structures can carry in-plane and out-of-plane loads and exhibit good stability under compression, keeping excellent strength to weight and stiffness to weight characteristics. In order to use these materials in different applications, the knowledge of their static behavior is required and a better understanding of the various failure mechanisms under static loading condition is necessary and highly desirable. The objective of this study is to develop a modeling approach to predict response of composite sandwich panels under static bending conditions. Different models including 2D and 3D with orthotropic material properties were attempted in advanced finite element (FE) software Ansys. Comparison of FE model predictions with experimental data on sandwich panel bending properties helped in establishing appropriate modeling approach. Analytical solutions were also used to verify the some of the mechanical properties such as bending stress and shear stress with the FEM results. For this study nomax flex core is used as a core material (thickness 15mm) and carbon fiber reinforced polymer composite (thickness 1.2mm each) is used as face sheet material. The experimental load of sandwich panels was taken and applied in steps through FEM and compared the results with experimental one at all steps. 3. DESCRIPTION OF PROBLEM A study of composite sandwich panel, under uniform static three point bend loading with undamaged models is considered for study. The sandwich panel consists of 8 layers of GFC plate at top and bottom face sheet, each layer has 0.15mm thickness and core is present between top and bottom face sheets which has 15mm thickness. A sandwich panel that consists of GFC face sheets and aluminum honeycomb core has been considered for the analysis. 4. FINITE ELEMENT MODELING CQUAD4 Element Coordinate System The element coordinate systems for the CQUAD4 is shown in Figure. The orientation of the element coordinate system is determined by the order of the connectivity for the grid points. The element z-axis, often referred to as the positive normal, is determined using the right-hand rule. Therefore, if you change the order of the grid points connectivity, the direction of this positive normal might also reverse. This rule is important to remember when you re applying pressure loads or viewing the element forces or stresses. Often, element stress contours appear to be strange when they re displayed by a post-processor because the normals of the adjacent elements may be inconsistent. The element s x-axis bisects the angle 2α. The positive direction is from G1 to G2. The element s y-axis is perpendicular to the element x-axis and lies in the plane defined by G1, G2, G3, and G4. The positive direction is from G1 to G4. The element s z-axis is normal to the x-y plane of the element. The positive z direction is defined by applying the right-hand rule to the ordering sequence of G1 through G4. Volume 3, Issue 12, December 2015 Page 55

4 CQUAD4 Element Geometry and Coordinate Systems CQUAD4 Format: The format of the CQUAD4 entry is as follows: Field Contents: EID - Element identification number. PID - Property identification number of a PSHELL or PCOMP entry. Gi - Grid point identification numbers of connection points. THETA-Material property orientation angle in degrees. MCID - Material coordinate system identification number. ZOFFS - Offset from the surface of grid points to the element reference plane. Ti - Membrane thickness of element at grid points G1 through G4. Grid points G1 through G4 must be ordered consecutively around the perimeter of the element. THETA and MCID are not required for homogenous, isotropic materials. ZOFFS is used when offsetting the element from its connection point. The continuation entry is optional. If you don t supply values for T1 to T4, the software sets them equal to the value of T (plate thickness) you define on the PSHELL entry. Finally, all interior angles of the CQUAD4 element must be less than Meshing in Hypermesh The CAD model is imported to Hypermesh and the geometry cleanup is done. The appropriate element size is selected according to the geometry features. Then using quad element the aluminum honeycomb is meshed and then the composite plates maintaining the connectivity. The meshed model is checked for element criteria. Volume 3, Issue 12, December 2015 Page 56

5 Table 1: Meshing details Element type Quad 4 Element size 3 No of elements No of nodes MATERIAL PROPERTIES OF SANDWICH PANEL Table 2: Material properties Aluminum core: Property Value Young s Modulus, E 68.9 GPa Poisson s Ratio,ν 0.33 Density, ρ 2700 kg/m3 Yield Stress, σyield 214 MPa Ultimate Tensile Stress, σuts 241 MPa Table 2: Material properties of Glass fibers Property Value Longitudinal Modulus, E 1 59 GPa Lateral Modulus, E 2 20GPa Poisson s Ratio,ν 0.35 Lonitudinal tension strength X t 2000 MPa Lonitudinal compression strength X c 1240 MPa Transverse tension strength Y t 82 MPa Transverse compression strength Y c 200 MPa Density, ρ 2.02 g/cm 3 In plane shear S 165 MPa The composite panel is made of 8 layers of Glass fiber sheets arranged with different degree of orientation. The layers of thickness 0.15mm are arranged as, 45 o,90 o,-45 o,-90 o,45 o,90 o,-45 o,-90 o.the top and bottom layers are arranged as in the order by total 16 layers. The Aluminum core is sandwiched between the layers. 7.Conclusion Various last researches on this topic were studied. Requirement for analysis of three point bending on honeycomb panel was made i.e. material properties of different materials used, accordingly meshing was done. The honeycomb panel studied in this paper has 8 layers of glass fiber arranged in different orientation. This different orientation of glass fiber should be taken into consideration during static analysis. References [1] Belouettar, S., Abbadi, A., Azari, Z., Belouettar, R., &Freres, P. (2009). Experimental investigation of static and fatigue behaviour of composites honeycomb materials using four point bending tests. Composite Structures, 87(3), [2] Isaac M. Daniel, Jandro L. Abot, J. L. (2000). Fabrication, testing and analysis of composite sandwich beams. [3] Herranen, H., Pabut, O., Eerme, M., Majak, J., Pohlak, M., Kers, J.,...&Aruniit, A. (2012). Design and testing of sandwich structures with different core materials. Materials Science, 18(1), [4] Hualin Fan, Lin Yang, Fangfang Sun, Daining FangFan, H., Yang, L., Sun, F., & Fang, D. (2013). Compression and bending performances of carbon fiber reinforced lattice-core sandwich composites. Composites Part A: Applied Science and Manufacturing, 52, [5] Jin Zhang, Peter Supernak, Simon Mueller-Alander, Chun H. Wang Improving the bending strength and energy absorption of corrugated sandwich composite structure Elsevier, Materials and Design 52 (2013) [6] KavehKabir, Tania Vodenitcharova, Mark Hoffman, Response of aluminium foam-cored sandwich panels to bending load Elsevier,Composites: Part B 64 (2014) Volume 3, Issue 12, December 2015 Page 57

6 [7] Craig A. Steeves, Norman A. Fleck, Collapse mechanisms of sandwich beams with composite faces and a foam core, loaded in three-point bending, International Journal of Mechanical Sciences 46 (2004) [8] V. Crupi, G. Epasto, E. Guglielmino, Comparison of aluminium sandwiches for lightweight ship structures: Honeycomb vs. foam, Elsevier, Marine Structures 30 (2013) [9] K.KanthaRao, K. JayathirthaRaoA.G.Sarwade, M.Sarath Chandra, Strength Analysis on Honeycomb Sandwich Panels of different Materials, International Journal of Engineering Research and Applications (IJERA) ISSN: [10] M.M. Venugopal, S K Maharana, K S Badarinarayan, Finite Element Evaluation of Composite Sandwich Panel Under Static Four Point Bending Load, JEST-M, Vol. 2, Issue 1, 2013 Volume 3, Issue 12, December 2015 Page 58