A sandwich composite is fabricated by attaching two thin stiff skins to alightweight thick core. The core material is a low strength material, but dueto high thickness of the sandwich composite yields with high bending stiffnesswith overall low density. balsa wood, syntactic foam Open cell and closed cellstructured foam and composite honeycomb are mainly used core materials. Glassor carbon fiber reinforced laminates are widely used as skin materials. Sheetmetal is also used as skin materials in some cases.
They are commonly beingused in ship construction, building, bridges, trains, car doors, panels etc. Inconstruction new green sandwich structures are also being introduced where thecore is usually made from the natural materials (wood) and the skin is madefrom earth (clay) instead of cement. Thus making it more environmentfriendly. Generally,the sandwich composites are symmetric, the core configuration plays major rolein variations of sandwich component construction The core of a sandwichstructure can be any material, but in general they are classified into fourdifferent types; honeycomb core, foam or solid core, web core and corrugated ortruss core.
For the functioning of the sandwich structure as a whole thebinding of core and face sheets is another important criterion. The basic concept of asandwich structure is that the face sheets carry the bending loads while thecore carries the shear loads. The face sheets are strong and stiff in tensionand compression compared to the low density core material, whose primarypurpose is to keep the face sheets separated in order to maintain a highsection modulus (a high “moment of inertia” or “second moment of the area”).The core material has relatively low density (e.
g., honeycomb or foam), whichresults in high specific mechanical properties, in particular, high flexuralstrength and stiffness properties relative to the overall panel density.Therefore, sandwich panels are efficient in carrying bending loads.
Also, theyprovide increase in buckling resistance to shear panels and compressionmembers. Sandwich construction results in lower lateral deformations, higherbuckling resistance and higher natural frequencies than monocoqueconstructions. A sandwich structure operates in the same way with thetraditional I-beam, which has two flanges and a web connecting the flanges. Theconnecting web makes it possible for the flanges to act together and resistshear stresses. Sandwich structure and an I-beam differ from each other that,in a sandwich composite the core and laminates are different materials and thecore provides continuous support for the laminates rather than beingconcentrated in a narrow web. When the structure is subjected to bending, thelaminates act together, resisting the external bending moment so that onelaminate is loaded in compression and the other in tension. The core resiststransverse forces, at the same time, supports the laminates and stabilizes themagainst buckling and wrinkling.