A composite is a material engineered from two or more materials with different physical or chemical properties.

Composites classification is generally done based on the material used for the matrix.

In the field of civil engineering, the classification of composite materials plays a crucial role in understanding their applications and selection for various construction projects.

Composites can be classified based on the type of reinforcement, matrix material, or the manufacturing process .

Composite materials examples in civil engineering include reinforced concrete, fiber-reinforced polymer (FRP) composites, and wood-plastic composites. These materials are made of a combination of high-strength fibers or particles embedded in a matrix material, such as cement, polymer, or metal.

Composite materials are classified into different categories based on the type of reinforcement, such as particulate, fibrous, or laminar.

Composite materials list can also be organized according to the matrix material, including polymer, metal, and ceramic composites.

The classification of polymer composites is particularly important, as they are widely used in infrastructure, building materials, and transportation applications.

Composites are strong heterogenous materials. From point to point the properties vary. It is based on the type of material phase present at that point.

Fiber reinforced composites do not display plastic properties like their parents. They are more sensitive to stress concentrations.

The combination of distinct materials does not blend with one another and provides a new material with unique properties which differ from individual constituents.

Functions of constituents

The two constituents include matrix and reinforcement,

1. Matrix–  Holds fibers together, protection from environment, load distribution, 

enhancing properties like impact resistance and providing smooth surface finish.

2. Reinforcement – contribution of desired properties, transfer of strength to matrix and load carrying.

Due to the availability of a wide variety of these constituents the design potentials     are incredible.

Composites Classification

Composites are categorized at two levels of classification, fist level is based on matrix constituents and second level is on reinforcement type.

Composites Classification based on matrix constituents

The matrix is usually in continuous phase throughout the component.

Polymer Matrix Composite (PCMs)

Main function of PMCs is to transfer load along the fiber. 

It contains short continuous fibers bound by a polymeric matrix. High stiffness, corrosion resistance, abrasion resistance, and high strength along the direction of fibers are some of the properties of PMCs.

Metal Matrix Composite (MMCs)- 

It is a material in which carbon, silicon carbide or ceramic fibers are embedded in a metal matrix.

 Usually aluminum is used instead of iron because of its low density and high strength. 

MMCs have increased specific strength, specific stiffness,  wear resistance at elevated temperature, low density and good corrosion resistance.

Ceramic Matrix Composite (CMCs)- 

It contains carbon or ceramic fiber surrounded by a ceramic matrix like silicon carbide.

Composites based on type of reinforcement form

Particulate form 

In this, reinforcement is in particle form which is dispersed or scattered  in softer  metallic or ceramic or polymer matrices.

A widely used particulate composite is concrete in which gravel is embedded in cement paste.

Flake composite 

Composites are obtained by blending flakes with matrix material. Flakes can be made to align with one another to obtain orderly structure than particulate composite.

Fiber Reinforced Composite (FRCs)- 

Fibrous composites are strong and stiff in nature due to presence of strong reinforcement in the form of fibers bound by matrix.

In FRC the load is distributed from one fiber to adjacent fiber under excessive load. These are of high strength, corrosion resistant and low density.

Carbon fiber, glass fibers and Aramid fibers are most usually used as reinforcements.

Laminated composites

These are  in layer form bounded by thin elementary layers. Composite layered materials are mostly encountered in high performing structures.

Types of Matrix and Reinforcements

Matrix- Organic matrix can either be thermosets, thermoplastic or elastomers. The widely used matrix are as follows

Thermosetting–  unsaturated polyester, epoxy resins, vinyl ester resins, phenols.

Thermo-plastic– polypropylene(PP), polyamide(PA), polycarbonate(PC) , poly-ether-ether-ketone(PEEK).

Elastomers– polyurethane (PU), silicon(Si).

Of all the above matrix materials thermosetting are mostly used as they are stable, strong, and unmelt able when subjected to curing or cross linking.

 Thermoplastics itself says that they are reversible  as they melt when exposed to heat. 

Reinforcements- The fibers mainly used as reinforcements are:

Carbon fibers, glass fibers, boron fibers, ceramic fibers, metal fibers, Aramid fibers, natural fibers like sisal, hemp, flax, etc.

Filler additives are incorporated into composites with a motive of improving particular characteristics of the material. 

The number of added products varies depending on the property we need to achieve. In general they are made to improve the processability of the material.

Structural classification

Unlike the matrix and reinforcement classifications. Composites are further classified based on their structure.

 Sandwich structure

contains multiple layers with different functions and properties. Just like a sandwich, it contains a core layer bounded by face sheets.

This structure is most often used as  rigidity, high strength and stiffness is provided by the core material and is usually light weight.

The design differs depending upon the requirement of the specific application. Composites can be optimized with different core materials , face sheets and bonding techniques to obtain required properties.

Their unique properties and versatility , made them the best choice for many industrial applications.

Monolithic structure

 This is characterized by uniform and continuous structure. It is a single solid structure rather than merging of multiple components.

Monolithic structures are obtained by blending fiber and resin with no distinct boundaries or interface between them, and are uniform and continuous.

The absence of an interface reduces the risk of delamination, which is a common reason for failure  in traditional composites.

This made them highly desirable in applications where structural integrity and reliability are crucial. 

Monolithic composites are an advanced form of composites that offer unique properties because of its continuous and seamless structure.

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