materials science Materials science is an interdisciplinary field of researching and discovering materials. Materials engineering is an engineering field of finding uses for materials in other fields and industries. The intellectual origins of materials sci ...

, a sandwich-structured composite is a special class of

composite material A composite or composite material (also composition material) is a material which is produced from two or more constituent materials. These constituent materials have notably dissimilar chemical or physical properties and are merged to create a ...

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

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 ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...

. Open- and closed-cell-structured

foam Foams are two-phase materials science, material systems where a gas is dispersed in a second, non-gaseous material, specifically, in which gas cells are enclosed by a distinct liquid or solid material. Note, this source focuses only on liquid ...

s like Polyethersulfone, polyvinylchloride,

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

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 bott ...

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

foams, balsa wood, syntactic foams, and

honeycomb A honeycomb is a mass of Triangular prismatic honeycomb#Hexagonal prismatic honeycomb, hexagonal prismatic cells built from beeswax by honey bees in their beehive, nests to contain their brood (eggs, larvae, and pupae) and stores of honey and pol ...

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 In materials science, a metal foam is a material or 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) ...

can also be used as core materials.

Laminate Simulated flight (using image stack created by μCT scanning) through the length of a knitting needle that consists of laminated wooden layers: the layers can be differentiated by the change of direction of the wood's vessels Shattered windshi ...

s of

glass Glass is an amorphous (non-crystalline solid, non-crystalline) solid. Because it is often transparency and translucency, transparent and chemically inert, glass has found widespread practical, technological, and decorative use in window pane ...

carbon Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...

fiber-reinforced

thermoplastic A thermoplastic, or thermosoftening 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 as ...

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 and ...

polymers ( unsaturated polyesters, epoxies...) are widely used as skin materials.

Sheet metal Sheet metal is metal formed into thin, flat pieces, usually by an industrial process. Thicknesses can vary significantly; extremely thin sheets are considered foil (metal), foil or Metal leaf, leaf, and pieces thicker than 6 mm (0.25 ...

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 advantage ...

or with metal components by

brazing Brazing is a metal-joining process in which two or more metal items are joined 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 welding in ...

together.

History

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

Archimedes Archimedes of Syracuse ( ; ) was an Ancient Greece, Ancient Greek Greek mathematics, mathematician, physicist, engineer, astronomer, and Invention, inventor from the ancient city of Syracuse, Sicily, Syracuse in History of Greek and Hellenis ...

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

Vitruvius Vitruvius ( ; ; –70 BC – after ) was a Roman architect and engineer during the 1st century BC, known for his multi-volume work titled . As the only treatise on architecture to survive from antiquity, it has been regarded since the Renaissan ...

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

Leonardo da Vinci Leonardo di ser Piero da Vinci (15 April 1452 - 2 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 o ...

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. Theory If the section is symmetric, isotropic and is not curved before a bend occurs, th ...

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 ...

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), commonly referred to as Galileo Galilei ( , , ) or mononymously as Galileo, was an Italian astronomer, physicist and engineer, sometimes described as a poly ...

describes the efficiency of tubes versus solid rods. * 1652 Wendelin Schildknecht reports about sandwich beam structures with curved wooden beam reinforcements. * 1726 Jacob Leupold 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 French royal palace located on Rue Saint-Honoré in the 1st arrondissement of Paris. The screened entrance court faces the Place du Palais-Royal, opposite the Louvre Palace, Louvre. Originally called the Palais-Ca ...

in Paris. * 1802 Jean-Baptiste Rondelet analyses and documents the

sandwich A sandwich is a Dish (food), dish typically consisting variously of meat, cheese, sauces, and vegetables used as a filling between slices of bread, or placed atop a slice of bread; or, more generally, any dish in which bread serves as a ''co ...

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/rotational mass, second moment of mass, or most accurately, rotational inertia, of a rigid body is defined relatively to a rotational axis. It is the ratio between ...

for sandwich constructions. * 1830

Robert Stephenson Robert Stephenson , (honoris causa, Hon. causa) (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 hi ...

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 (14 May 1884 – 5 December 1969) was a Franco-German airplane designer and founder of Dornier GmbH. His notable designs include the 12-engine Dornier Do X flying boat, for decades the world's la ...

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 (pronounced , ) 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 ...

Mosquito Mosquitoes, the Culicidae, are a Family (biology), family of small Diptera, flies consisting of 3,600 species. The word ''mosquito'' (formed by ''Musca (fly), mosca'' and diminutive ''-ito'') is Spanish and Portuguese for ''little fly''. Mos ...

was built with sandwich composites; a balsawood core with

plywood Plywood is a composite material manufactured from thin layers, or "plies", of wood veneer that have been stacked and glued together. It is an engineered wood from the family of manufactured boards, which include plywood, medium-density fibreboa ...

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 several important benefits: It saves waste paper from occupying the homes of people and producing methane as it breaks down. Because paper fibr ...

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, wall dividers and terrace boards. 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 astron ...

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 is any of various structural members with an - (serif capital letter 'I') or H-shaped cross section (geometry), cross-section. Technical terms for similar items include H-beam, I-profile, universal column (UC), w-beam (for "wide flang ...

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

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

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 panel A sandwich panel is any structure made of three layers: a low-density core ( PIR, mineral wool, XPS), and a thin skin-layer bonded to each side. Sandwich panels are used in applications where a combination of high structural rigidity and low ...

s, with different types such as FRP sandwich panel,

aluminium composite panel A sandwich panel is any structure made of three layers: a low-density core (Polyisocyanurate, PIR, mineral wool, Polystyrene#Extruded polystyrene (XPS), XPS), and a thin skin-layer bonded to each side. Sandwich panels are used in applications ...

, 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, 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 Science Biology * Seashell, a hard outer layer of a marine ani ...

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

linear In mathematics, the term ''linear'' is used in two distinct senses for two different properties: * linearity of a '' function'' (or '' mapping''); * linearity of a '' polynomial''. An example of a linear function is the function defined by f(x) ...

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 * Radio beam *Particle beam, a stream of charged or neutral particles ** Charged particle beam, a spatially ...

. 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