Composite Materials

Dr. Ruwan Gallage

ME 2302 : Introduction to Materials Science andManufacturing Engineering

Part A: Engineering Materials

Many of our modern technologies require materials with unusual combinations of properties that cannot be met by the conventional metal alloys, ceramics, and polymeric materials. This is especially true for materials that are needed for aerospace, underwater, and transportation applications.

For example, aircraft engineers are increasingly searching for structural materials that have low densities, strong, stiff, abrasion and impact resistant, and are not easily corroded.

WHY STUDY Composites?

Boeing 787

What is composite material?

There are no universally accepted definition. If a material satisfied the following condition is called as composite ;

(a) It consists of two or more physically and/or chemically distinct , suitably arranged or distributed phases.

(b) It has properties that are different from either parent material.(c) It is manufactured. (Except wood, bone)

Many composite materials are composed of just two phases; one is termed the matrix, which is continuous and surrounds the other phase, often called the dispersed phase (fiber or particles).

Composites that occur in nature: Wood consists of strong and flexible cellulose fibers surrounded and held together by a stiffer material called lignin. Bone is a composite of the strong yet soft protein collagen and the hard, brittle mineral apatite.

Example for composite materials use in Engineering are concrete, chip board, fiber reinforced composite, etc.

(a) Classification of composites according to the reinforcement geometry

1. Fiber-reinforced composites2. Particulate composites3. Structural composites ( Laminar, sandwich)

Automobile tires

matrix:(Rubber)

Particles(Carbon)

1. Fiber-reinforced composites

Excellent strength-to-weight ratio, stiffness and fatigue resistance

Consist of two phases: the fiber and matrix

1. Glass fibers: Glass fibers are silica (~50 %) based. Quite cheap and use for reinforcement of plastics (Fiberglass)

2. Carbon fibers: Carbon is a very light element. Graphite form is considered for carbon fibers.

3. Ceramics fibers: Commonly use Al2O3 fibers, SiC fibers. Possibility to use at high temperature , Chemically inert.

4. Organic fibers: Kevlar (commercial name)

5. Metallic fibers: Wire form of Ti, W, Ta, Mo etc.

Types of fibers

The fiber are responsible for handling the applied load.

Types of matrix

1. Polymeric materials: Polyester resin (commonly use due to low cost), epoxy resins, vinyl ester resin

2. Metal : Super alloys, Aluminum (Al), Magnesium(Mg), Titanium(Ti), Cupper(Cu ) and their alloys

3. Ceramics: Alumina (Al2O3,), Zirconia (ZrO2)

The matrix must- be able to transfer the mechanical load to the fiber, - be able to protect the individual fibers from surface damage

as a result of mechanical abrasion or chemical reactions with the environment,

- has adequate adhesive bonding forces between fiber to minimize fiber pull-out to get the ultimate strength of composite

1. Fiber-reinforced composite

Impact of the fiber amount and orientation on performance of composite

1. Fiber-reinforced composites

Most fiber reinforced composite contain 35 % to 50% of fibers by volume. (When fiber fraction exceeds about 80%, there is not enough matrix materials to completely surrounded the fiber and transfer the load effectively.)

Aligned fibers results in the more reinforcing in aligned direction than any other direction. Randomly oriented fibers are isotropic and providing same properties in all direction. Produce more easier and inexpensive Fabric fibers results in higher strength and ability to withstand loads in multiple directions. More complicated and manufacturing process is expensive.

2. Particulate composites

Cannot provide the same strength as fiber reinforced composites but much easier to manufacture and inexpensive

Contain large number of particles called aggregates that help to withstand composite in compressive loads. Possessing the same properties in all direction (Isotropic)

Most common particulate composites are Portland cement concrete and Asphalts concrete (Mineral aggregates with tar and binders, etc., use for constructing roadways and parking lots.) .

Concrete Asphalts concrete

3. Structural composites ( Laminar, Sandwich)

Normally composed of both homogeneous materials and composite materials, the properties of which depend not only on the properties of the constituent materials but also on the geometrical design of the various structural elements.

Laminar composite

Composed of two-dimensional sheets or panels that have a preferred high-strength directional arrangement of fibers. (such as found in wood and continuous and aligned fiber-reinforced plastics). The layers are stacked and subsequently cemented together such that the orientation of the high-strength direction varies with each successive layer.

Sandwich composite

. Consists of two outer sheets that are separated and adhesively bonded to a thicker core.

The outer sheets are made of a relatively stiff and strong material, typically aluminum alloys, fiber-reinforced plastics, titanium, steel, or plywood; they impart high stiffness and strength to the structure, and must be thick enough to withstand tensile and compressive stresses that result from loading.

The core material is lightweight. Core materials typically fall within three categories: rigid polymeric foams (i.e., phenolics, epoxy), wood and honeycombs

(b) Classification of composites according to the matrix materials:1. Polymer-matrix composite (PMC)2. Metal-matrix composite (MMC)3. Ceramic-matrix composite (CMC)

Fracture surface of a SiC fibre-reinforced Cu metal matrix composite

1. Polymer- matrix composite (PMC)

Polymer resin as the matrix, with fibers as the reinforcement medium.

These materials are wildly used in various applications, as well as in the largest quantities, due to room-temperature properties, ease of fabrication, and cost.

1.1 Glass Fiber-Reinforced Polymer Composites (Fiberglass)

It is readily available and may be fabricated into a glass-reinforced plastic economically using a wide variety of composite-manufacturing techniques. When coupled with the various plastics, it can be used in a variety of corrosive environments.

Applications: Automotive and marine bodies, plastic pipes, storage containers, and industrial floorings. (The transportation industries are utilizing these to decrease vehicle weight and boost fuel efficiencies)

1.2 Carbon Fiber-Reinforced Polymer Composites

Carbon fibers have the highest specific modulus and specific strength of all reinforcing fiber materials.

At room temperature, carbon fibers are not affected by moisture or a wide variety of solvents, acids, and bases.

These fibers exhibit a diversity of physical and mechanical characteristics.

Expensive than other composites ( However, manufacturing processes have been developed that are relatively inexpensive and cost effective)

Applications: Sports equipment (fishing rods, golf clubs), pressure vessels, and aircraft structural components.

2. Metal - matrix composite (MMC)

Ductile metal as the matrix, with fibers as the reinforcement medium.

May be utilized at higher service temperatures than their base metal counterparts.

Some of the advantages of these materials over the polymer-matrix composites(PMC) include higher operating temperatures, nonflammability, and greater resistance to degradation by organic fluids.

Much more expensive than PMC.

Applications: Automobile industries (some engine components -aluminum-alloy matrix with carbon fibers), extruded stabilizer bars, transmission components.

3. Ceramic- matrix composite (CMC)

Ceramic materials are inherently resilient to oxidation and deterioration at elevated temperatures. Some of these materials would be ideal candidates for use in high-temperature applications, specifically for components in automobile and aircraft gas turbine engines.

Referencess:1. http://en.wikipedia.org/wiki/Ceramic_matrix_composite2. http://en.wikipedia.org/wiki/Metal_matrix_composite3. http://en.wikipedia.org/wiki/Composite_material