A sandwich-structured composite is a special class of

composite material A composite material (also called a composition material or shortened to composite, which is the common name) is a material which is produced from two or more constituent materials. These constituent materials have notably dissimilar chemical or ...

s that is fabricated by attaching two thin but stiff skins to a lightweight but thick core. The core material is normally low strength material, but its higher thickness provides the sandwich composite with high

bending In applied mechanics, bending (also known as flexure) characterizes the behavior of a slender structural element subjected to an external load applied perpendicularly to a longitudinal axis of the element. The structural element is assumed to ...

stiffness Stiffness is the extent to which an object resists deformation in response to an applied force. The complementary concept is flexibility or pliability: the more flexible an object is, the less stiff it is. Calculations The stiffness, k, of a ...

with overall low

density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematicall ...

. Open- and closed-cell-structured

foam Foams are materials formed by trapping pockets of gas in a liquid or solid. A bath sponge and the head on a glass of beer are examples of foams. In most foams, the volume of gas is large, with thin films of liquid or solid separating the ...

s like

polyethersulfone Polysulfones are a family of high performance thermoplastics. These polymers are known for their toughness and stability at high temperatures. Technically used polysulfones contain an aryl- SO2-aryl subunit. Due to the high cost of raw material ...

polyvinylchloride,

polyurethane Polyurethane (; often abbreviated PUR and PU) refers to a class of polymers composed of organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethane is produced from ...

polyethylene Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging ( plastic bags, plastic films, geomembranes and containers including b ...

polystyrene Polystyrene (PS) is a synthetic polymer made from monomers of the Aromatic hydrocarbon, aromatic hydrocarbon styrene. Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and brittle. It is an inexpensive resin pe ...

foams,

balsa wood ''Ochroma pyramidale'', commonly known as the balsa tree, is a large, fast-growing tree native to the Americas. It is the sole member of the genus ''Ochroma''. The tree is famous for its wide usage in woodworking, with the name ''balsa'' bei ...

, syntactic foams, and

honeycomb A honeycomb is a mass of hexagonal prismatic wax cells built by honey bees in their nests to contain their larvae and stores of honey and pollen. Beekeepers may remove the entire honeycomb to harvest honey. Honey bees consume about of honey ...

s are commonly used core materials. Sometimes, the honeycomb structure is filled with other foams for added strength. Open- and closed-cell

metal foam Regular foamed aluminium A metal foam is a cellular structure consisting of a solid metal (frequently aluminium) with gas-filled pores comprising a large portion of the volume. The pores can be sealed (closed-cell foam) or interconnected (open- ...

can also be used as core materials.

Laminate Lamination is the technique/process of manufacturing a material in multiple layers, so that the composite material achieves improved strength, stability, sound insulation, appearance, or other properties from the use of the differing materia ...

s of

glass Glass is a non- crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenchin ...

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...

fiber-reinforced

thermoplastic A thermoplastic, or thermosoft plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling. Most thermoplastics have a high molecular weight. The polymer chains associate ...

s or mainly

thermoset In materials science, a thermosetting polymer, often called a thermoset, is a polymer that is obtained by irreversibly hardening (" curing") a soft solid or viscous liquid prepolymer ( resin). Curing is induced by heat or suitable radiation ...

polymers ( unsaturated polyesters,

epoxies The Epoxies were an American new wave band from Portland, Oregon, formed in 2000. Heavily influenced by new wave, the band jokingly described themselves as robot garage rock. Members included FM Static on synthesizers, guitarist Viz Spectrum, l ...

...) are widely used as skin materials.

Sheet metal Sheet metal is metal formed into thin, flat pieces, usually by an industrial process. Sheet metal is one of the fundamental forms used in metalworking, and it can be cut and bent into a variety of shapes. Thicknesses can vary significantly; ex ...

is also used as skin material in some cases. The core is bonded to the skins with an

adhesive Adhesive, also known as glue, cement, mucilage, or paste, is any non-metallic substance applied to one or both surfaces of two separate items that binds them together and resists their separation. The use of adhesives offers certain advant ...

or with metal components by

brazing Brazing is a metal-joining process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, with the filler metal having a lower melting point than the adjoining metal. Brazing differs from ...

together.

History

A summary of the important developments in sandwich structures is given below. * 230 BC

Archimedes Archimedes of Syracuse (;; ) was a Greek mathematician, physicist, engineer, astronomer, and inventor from the ancient city of Syracuse in Sicily. Although few details of his life are known, he is regarded as one of the leading scientis ...

describes the laws of levers and a way to calculate density. * 25 BC

Vitruvius Vitruvius (; c. 80–70 BC – after c. 15 BC) was a Roman architect and engineer during the 1st century BC, known for his multi-volume work entitled '' De architectura''. He originated the idea that all buildings should have three attribut ...

reports about the efficient use of materials in Roman truss roof structures. * 1493

Leonardo da Vinci Leonardo di ser Piero da Vinci (15 April 14522 May 1519) was an Italian polymath of the High Renaissance who was active as a painter, draughtsman, engineer, scientist, theorist, sculptor, and architect. While his fame initially rested on ...

discovers the

neutral axis The neutral axis is an axis in the cross section of a beam (a member resisting bending) or shaft along which there are no longitudinal stresses or strains. If the section is symmetric, isotropic and is not curved before a bend occurs, then the ne ...

and load deflection relation in three-point bending. * 1570

Palladio Andrea Palladio ( ; ; 30 November 1508 – 19 August 1580) was an Italian Renaissance architect active in the Venetian Republic. Palladio, influenced by Roman and Greek architecture, primarily Vitruvius, is widely considered to be one of t ...

presents truss- beam constructions with diagonal beams to prevent shear deformations. * 1638

Galileo Galilei Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642) was an Italian astronomer, physicist and engineer, sometimes described as a polymath. Commonly referred to as Galileo, his name was pronounced (, ). He ...

describes the efficiency of tubes versus solid rods. * 1652 Wendelin Schildknecht reports about sandwich beam structures with curved wooden beam reinforcements. * 1726

Jacob Leupold Jacob Leupold (22 July 1674 – 12 January 1727) was a German physicist, mathematician, instrument maker, mining commissioner and engineer. He wrote the seminal book ''Theatrum Machinarum Generale'' ("The General Theory of Machines"). Early lif ...

documents tubular bridges with compression loaded roofs. * 1786 Victor Louis uses iron sandwich beams in the galleries of the

Palais-Royal The Palais-Royal () is a former royal palace located in the 1st arrondissement of Paris, France. The screened entrance court faces the Place du Palais-Royal, opposite the Louvre. Originally called the Palais-Cardinal, it was built for Cardinal R ...

in Paris. * 1802

Jean-Baptiste Rondelet Jean-Baptiste Rondelet (4 June 1743 – 25 September 1829) was an architectural theorist of the late Enlightenment era and chief architect of the church of Sainte-Geneviève after the death of Jacques Germain Soufflot of cancer in 1780. Ron ...

analyses and documents the

sandwich A sandwich is a food typically consisting of vegetables, sliced cheese or meat, placed on or between slices of bread, or more generally any dish wherein bread serves as a container or wrapper for another food type. The sandwich began as a po ...

effect in a beam with spacers. * 1820 Alphonse Duleau discovers and publishes the

moment of inertia The moment of inertia, otherwise known as the mass moment of inertia, angular mass, second moment of mass, or most accurately, rotational inertia, of a rigid body is a quantity that determines the torque needed for a desired angular accele ...

for sandwich constructions. * 1830

Robert Stephenson Robert Stephenson FRS HFRSE FRSA DCL (16 October 1803 – 12 October 1859) was an English civil engineer and designer of locomotives. The only son of George Stephenson, the "Father of Railways", he built on the achievements of his father ...

builds the Planet locomotive using a sandwich beam frame made of wood plated with iron * 1914 R. Höfler and S. Renyi patent the first use of honeycomb structures for structural applications. * 1915

Hugo Junkers Hugo Junkers (3 February 1859 – 3 February 1935) was a German aircraft engineer and aircraft designer who pioneered the design of all-metal airplanes and flying wings. His company, Junkers Flugzeug- und Motorenwerke AG (Junkers Aircraft and ...

patents the first honeycomb cores for aircraft application. * 1934 Edward G. Budd patents welded steel honeycomb sandwich panel from corrugated metal sheets. * 1937

Claude Dornier Claude (Claudius) Honoré Désiré Dornier (born in Kempten im Allgäu on 14 May 1884 – 5 December 1969) was a German-French airplane designer and founder of Dornier GmbH. His notable designs include the 12-engine Dornier Do X flying boa ...

patents a honeycomb sandwich panel with skins pressed in a plastic state into the core cell walls. * 1938 Norman de Bruyne patents the structural adhesive bonding of honeycomb sandwich structures. * 1940 The

de Havilland The de Havilland Aircraft Company Limited () was a British aviation manufacturer established in late 1920 by Geoffrey de Havilland at Stag Lane Aerodrome Edgware on the outskirts of north London. Operations were later moved to Hatfield in H ...

Mosquito Mosquitoes (or mosquitos) are members of a group of almost 3,600 species of small flies within the family Culicidae (from the Latin ''culex'' meaning " gnat"). The word "mosquito" (formed by ''mosca'' and diminutive ''-ito'') is Spanish for "li ...

was built with sandwich composites; a balsawood core with

plywood Plywood is a material manufactured from thin layers or "plies" of wood veneer that are glued together with adjacent layers having their wood grain rotated up to 90 degrees to one another. It is an engineered wood from the family of manufactured ...

skins.

Types of sandwich structures

Metal composite material (MCM) is a type of sandwich formed from two thin skins of metal bonded to a plastic core in a continuous process under controlled pressure, heat, and tension.

Recycled paper The recycling of paper is the process by which waste paper is turned into new paper products. It has a number of important benefits: It saves waste paper from occupying homes of people and producing methane as it breaks down. Because paper fib ...

is also now being used over a closed-cell recycled kraft honeycomb core, creating a lightweight, strong, and fully repulpable composite board. This material is being used for applications including point-of-purchase displays, bulkheads, recyclable office furniture, exhibition stands, and wall dividers. To fix different panels, among other solutions, a transition zone is normally used, which is a gradual reduction of the core height, until the two fiber skins are in touch. In this place, the fixation can be made by means of bolts, rivets, or adhesive. With respect to the core type and the way the core supports the skins, sandwich structures can be divided into the following groups: homogeneously supported, locally supported, regionally supported, unidirectionally supported, bidirectionally supported. The latter group is represented by honeycomb structure which, due to an optimal performance-to-weight ratio, is typically used in most demanding applications including

aerospace Aerospace is a term used to collectively refer to the atmosphere and outer space. Aerospace activity is very diverse, with a multitude of commercial, industrial and military applications. Aerospace engineering consists of aeronautics and ast ...

Properties of sandwich structures

The strength of the composite material is dependent largely on two factors: :#The outer skins: If the sandwich is supported on both sides, and then stressed by means of a downward force in the middle of the beam, then the bending moment will introduce shear forces in the material. The shear forces result in the bottom skin in tension and the top skin in compression. The core material spaces these two skins apart. The thicker the core material the stronger the composite. This principle works in much the same way as an

I-beam An I-beam, also known as H-beam (for universal column, UC), w-beam (for "wide flange"), universal beam (UB), rolled steel joist (RSJ), or double-T (especially in Polish, Bulgarian, Spanish, Italian and German), is a beam with an or -shap ...

does. :#The interface between the core and the skin: Because the

shear stress Shear stress, often denoted by ( Greek: tau), is the component of stress coplanar with a material cross section. It arises from the shear force, the component of force vector parallel to the material cross section. '' Normal stress'', on ...

es in the composite material change rapidly between the core and the skin, the adhesive layer also sees some degree of shear force. If the adhesive bond between the two layers is too weak, the most probable result will be delamination. The failure of the interface between the skin and core is critical and the most common damage mode. The propensity of this damage to propagate through the interface or dive either into the skin or core is governed by the shear component.

Application of sandwich structures

Sandwich structures can be widely used in sandwich panels, these kinds of panels can be in different types such as FRP sandwich panel, aluminium composite panel etc. FRP polyester reinforced composite honeycomb panel (sandwich panel) is made of polyester reinforced plastic, multi-axial high-strength glass fiber and PP honeycomb panel in special antiskid tread pattern mold through the process of constant temperature vacuum adsorption & agglutination and solidification.

Theory

Sandwich theoryPlantema, F, J., 1966, Sandwich Construction: The Bending and Buckling of Sandwich Beams, Plates, and Shells, Jon Wiley and Sons, New York.Zenkert, D., 1995, An Introduction to Sandwich Construction, Engineering Materials Advisory Services Ltd, UK. describes the behaviour of a beam,

plate Plate may refer to: Cooking * Plate (dishware), a broad, mainly flat vessel commonly used to serve food * Plates, tableware, dishes or dishware used for setting a table, serving food and dining * Plate, the content of such a plate (for example: ...

, or

shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses ** Thin-shell structure Science Biology * Seashell, a hard o ...

which consists of three layers - two face sheets and one core. The most commonly used sandwich theory is

linear Linearity is the property of a mathematical relationship ('' function'') that can be graphically represented as a straight line. Linearity is closely related to '' proportionality''. Examples in physics include rectilinear motion, the linear ...

and is an extension of first order

beam theory Beam may refer to: Streams of particles or energy *Light beam, or beam of light, a directional projection of light energy **Laser beam *Particle beam, a stream of charged or neutral particles **Charged particle beam, a spatially localized grou ...

. Linear local buckling sandwich theory is of importance for the design and analysis of Sandwich plates or sandwich panels, which are of use in building construction, vehicle construction, airplane construction and refrigeration engineering.

References

{{reflist

External links

SandwichPanels.org
– Composite sandwich structure information
Diab Sandwich HandbookHoneycomb Sandwich Design TechnologyEngineered timber sandwich core materials
– Composite sandwich structure information

Application of aluminium honeycomb sandwich panel as an energy absorber of high-speed train nose Composite materials Aerospace materials