Composite Material

• A combination of two or more materials to form

• a new material system with enhanced material properties.

What are Composites?

• Composites: A combination of two or more materials (reinforcement, resin, filler, etc.), differing in form or composition on a macroscale. The constituents retain their identities, i.e.., they do not dissolve or merge into each other, although they act in concert. Normally, the components can be physically identified and exhibit an interface between each other.

• Composites: Artificially produced multiphase materials.• Composites: Design materials with properties better

than those of conventional materials (metals, ceramics, or polymers).

• Composites: materials, usually man-made, that are a three-dimensional combination of at least two chemically distinct materials, with a distinct interface separating the components, created to obtain properties that cannot be achieved by any of the components acting alone.

• Composites: are combinations of two materials in which one of the materials, called the reinforcing phase, is in the form of fibers, sheets, or particles, and is embedded in the other materials called the matrix phase. The reinforcing material and the matrix material can be metal, ceramic, or polymer.

• In their broadest form, composites are materials consist of two or more constituents. The constituents are combined in such a way that they keep their individual physical phases and are not soluble in each other or not to form a new chemical compound.

• One constituent is called reinforcing phase and the one in which the reinforcing phase is embedded is called matrix.

• Historical or natural examples of composites are abundant: brick made of clay reinforced with straw, mud wall with bamboo shoots, concrete, concrete reinforced with steel rebar, granite consisting of quartz, mica and feldspar, wood (cellulose fibers in lignin matrix), etc.

• Advanced Composites: Advanced composite materials are refereed to those composite materials developed and used in the aerospace industries. They usually consist of high performance fibers as reinforcing phases and polymers or metals as matrices.

• Definition: An advanced composite material comprises at least two chemically different materials (heterogeneity): a reinforcement, and a matrix that binds the reinforcement and is separated from it by a sharp interface.

• Dispersed phase within continuous phase

Phases of Composites• Matrix Phase: Polymers, Metals, Ceramics Also,

continuous phase, surrounds other phase (e.g.: metal, ceramic, or polymer)

• Reinforcement Phase: Fibers, Particles, or Flakes Also, dispersed phase, discontinuous phase (e.g.: metal, ceramic, or polymer)

• → Interface between matrix and reinforcement• Examples:– Jello and cole slaw/mixed fruit– Peanut brittle– Straw in mud– Wood (cellulose fibers in hemicellulose and lignin)– Bones (soft protein collagen and hard apatite minerals)– Pearlite (ferrite and cementite)

Factors in Creating CompositesFactors in creating composites:– Matrix material– Reinforcement material

• Ceramics: Ceramic materials are inorganic, nonmetallic materials. Most ceramics are compounds between metallic and nonmetallic elements for which the interatomic bonds are either totally ionic or predominantly ionic but having some covalent character.

• The term ceramic comes from the Greek word keramikos, which means burnt stuff, indicating that desirable properties of these materials are normally achieved through a hightemperature heat treatment process called firing.

The Main Characteristics OfComposite Materials

• (I) Heterogeneity: Non-uniformity of the chemical/physical structure

• (II) Anisotropy: Direction dependence of the physical properties

• (III) Symmetry: Tensorial nature of material properties• (IV) Hierarchy: Stacking of individual structural units• Moreover:• Interfacial properties - the interface may be regarded

as a third phase

Examples for composites• Fibre reinforced plastics:Classified by type of fiber: Wood (cellulose fibers in a lignin and hemicellulose

matrix)• Carbon-fibre reinforced plastic (CRP)• Glass-fibre reinforced plastic (GRP) (informally,• "fiberglass")• Classified by matrix:• Thermoplastic Composites• – short fiber thermoplastics• – long fiber thermoplastics or long fiber reinforced• thermoplastics• – glass mat thermoplastics• – continuous fiber reinforced thermoplastics• Thermoset Composites

• Reinforced carbon-carbon (carbon fibre in a graphite matrix)• Metal matrix composites (MMCs):• White cast iron• Hardmetal (carbide in metal matrix)• Metal-intermetallic laminate• Ceramic matrix composites:• Bone (hydroxyapatite reinforced with collagen fibers)• Cermet (ceramic and metal)• Concrete• Organic matrix/ceramic aggregate composites• Asphalt concrete• Dental composite• Syntactic foam• Mother of Pearl

Classification of Composites

• Composite materials are commonly classified at following two distinct levels:

• 1. The first level of classification: is usually made with respect to the matrix constituent. The major composite classes include Organic Matrix Composites (OMCs), Metal Matrix Composites (MMCs) and Ceramic Matrix Composites (CMCs). The term organic matrix composite is generally assumed to include two classes of composites, namely Polymer Matrix Composites (PMCs) and carbon matrix composites commonly referred to as carbon-carbon composites.

• 2. The second level of classification: refers to the reinforcement form - fibre reinforced composites, laminar composites and particulate composites. Fibre reinforced composites can be further divided into those containing discontinuous or continuous fibres.

Classification Based onReinforcements

• Fiber Reinforced Composites/Fibre Reinforced Polymer (FRP) Composites

• Laminar Composites• Particulate Reinforced Composites (PRC)

• Fibre Reinforced Composites are composed of fibres embedded in matrix material. Such a composite is considered to be a discontinuous fibre or short fibre composite if its properties vary with fibre length. On the other hand, when the length of the fibre is such that any further increase in length does not further increase, the elastic modulus of the composite, the composite is considered to be continuous fibre reinforced. Fibres are small in diameter and when pushed axially, they bend easily although they have very good tensile properties. These fibres must be supported to keep individual fibres from bending and buckling.

• Fiber Reinforced Polymer (FRP) Composites: "A matrix of polymeric material that is reinforced by fibers or other reinforcing material.”

• Laminar Composites: are composed of layers of materials held together by matrix. Sandwich structures fall under this category.

• Particulate Composites: are composed of particles distributed or embedded in a matrix body. The particles may be flakes or in powder form. Concrete and wood particle boards are examples of this category.

• Metal Matrix Composites (MMCs): A metal matrix composite (MMC) is a type of composite material with at least two constituent parts, one being a metal. The other material may be a different metal or another material, such as a ceramic or organic compound. When at least three materials are present, it is called a hybrid composite. An MMC is complementary to a cermet.

Role of Matrices in Composites

• Transfer stresses between the fibers.• Provide a barrier against an adverse environment.• Protect the surface of the fibers from mechanical

abrasion.• Determine inter-laminar shear strength.• Determine damage tolerance of composites.• Determine in-plane shear strength.• Determine the processibility of composites.• Determine heat resistance of composites

Advantages of Composites

• Summary of the advantages exhibited by composite materials, which are of significant use in aerospace industry are as follows:

• High resistance to fatigue and corrosion degradation.• High ‘strength or stiffness to weight’ ratio. As enumerated

above, weight savings are significant ranging from 25-45% of the weight of conventional metallic designs.

• Due to greater reliability, there are fewer inspections and structural repairs.

• Directional tailoring capabilities to meet the design requirements. The fibre pattern can be laid in a manner that will tailor the structure to efficiently sustain the applied loads.

• Fibre to fibre redundant load path.

• Improved dent resistance is normally achieved. Composite panels do not sustain damage as easily as thin gage sheet metals.

• It is easier to achieve smooth aerodynamic profiles for drag reduction. Complex double-curvature parts with a smooth surface finish can be made in one manufacturing operation.

• Composites offer improved torsional stiffness. This implies high whirling speeds, reduced number of intermediate bearings and supporting structural elements. The overall part count and manufacturing & assembly costs are thus reduced.

• High resistance to impact damage.• Like metals, thermoplastics have indefinite shelf life.

• Thermoplastics have rapid process cycles, making them attractive for high volume commercial applications that traditionally have been the domain of sheet metals. Moreover, thermoplastics can also be reformed.

• Composites are dimensionally stable i.e. they have low thermal conductivity and low coefficient of thermal expansion. Composite materials can be tailored to comply with a broad range of thermal expansion design requirements and to minimize thermal stresses.

• Manufacture and assembly are simplified because of part integration (joint/fastener reduction) thereby reducing cost.

• The improved weather ability of composites in a marine environment as well as their corrosion resistance and durability reduce the down time for maintenance.