Introduction to Composite Materials

Introduction to Composite Materials

• According to Balasubramanian, M. (2014), composite materials means a mix of two or more materials to achieve improved or desired properties
• Composite materials can be tailored for specific applications
• Composite materials examples include:
  • Concrete reinforced with steel which is gravel + cement + steel
  • Concrete is gravel + cement
  • Wood is lignin and cellulose
  • Asphalt concrete is binder and aggregate

Types of Composites

• There are natural composites as well as synthetic composites
• Natural composites include Wood made of Cellulose fibers and Lignin, Bone made of Hydroxyapatite and Collagen
• Synthetic composites include Fiberglass made of plastic and Glass, polyester made of coal,air,water, and petroleum, and plywood
• Composites have high strength, light weight, and can be tougher materials

Classification of Composite Materials

• Individual materials are also constituent materials
• Primary phase is a matrix
• Secondary phase is reinforcement
• Primary phase, also named matrix is the substance the secondary phase is embedded in
• Secondary phase, also named reinforcement is the substance in the matrix that serves to strengthen the composite material
• Role of the reinforcement is adds mechanical properties of strength and stiffness to the material
• Role of matrix is to bind the reinforcement together to distribute stress and protect the reinforcement
• Differences Between Matrix and Reinforcement:

Matrix

• Matrix is continuous
• Matrix is in greater quantity
• Matrix is based on 3 types referred to as PMC,CMC,MMC
• Matrix transfers the load
• Matrix protects individual fiber from surface damage due to abrasion and oxidation
• Example: alumina, aluminium, epoxy, polyester etc.

Reinforcement

• Reinforcement may be continuous or discontinuous
• Reinforcement type can be fibre reinforced or particulate
• Reinforcement bears the load
• Reinforcing phase provides strength and stiffness
• Reinforcement is stronger and harder than matrix
• Example: carbon, aramid, nylon, jute etc.

Types of Composite Materials

• Matrix is classified into three types: metal matrix composite (MMC), ceramic matrix composite (CMC), and polymer matrix composite (PMC)

Polymer Matrix Composites (PMC)

• Consist of different types of organic polymers combined with a fibrous reinforcement
• Are lightweight and have high stiffness and stength
• Are classified as Thermosets or Thermoplastics

Thermosets

• Examples include Epoxy and vulcanized rubber
• Are stronger than thermoplastic because of network transformation
• Cannot be melted and reshaped after they are cured

Thermoplastics

• Examples include Nylon and Polyethylene
• Can heated and shaped as a melted form into a new shape
• Does not show chemical property changes when heated or cooled multiple times

Metal Matrix Composites (MMC)

• Consist of low-density metal such as aluminum, magnesium, copper, or nickel, reinforced with particulate/fibers of ceramic, or graphite
• High strength regardless of temperature
• High stiffness
• Low density
• High thermal conductivity
• Costs are relatively high
• Used for fan blades in engines, brake linings, bicycle frames, etc.

Ceramic Matrix Composites (CMC)

• Consist of ceramic fibres embedded in a ceramic matrix
• Have high melting points
• Good compressive strength
• Good corrosion resistance
• Stable at high temperatures
• Excellent mechanical strength
• Conventional ceramics: alumina, aluminum nitride, silicon nitride, etc.
• Conventional ceramics fracture easily
• Applies to aerospace industry (gas turbines) and energy sector (heat exchangers).

Types of reinforcement in composites

• Types of reinforcement include particles or fiber

Fiber Reinforcement

• Reinforcement materials are fibers, which provide composite strength
• Cells are glued together by a matrix (epoxy, or polyester, etc.)
• Types of fibers include glass fibers, or fiberglass

Glass Fibers

• Most widely used fiber
• Either bottle glass fibers or high purity quartz glass
• Great tensile strength, moisture resistance, and thermal properties
• Low cost relative to other composites
• Moderate strength and weight

Advanced Fibers

• Includes carbon, boron, spectra fiber
• Boron has high stiffness but high costs
• Spectra fiber has high strength and are extremely light weight
• Carbon is the 2nd most widely used fiber
• Carbon also has low density, high stiffness and strength

Fiber Reinforcement: Fibre Orientation and Geometry

• Fibre orientation is a major factor influencing composite performance (strength)
  • Fiber Geometry
  • Aligned Fibers - best mechanical properties
    • Continuous: long fibers enable load transfer from matrix to fibers in order to effectively strengthen fiber composites
  • Discontinuous: shorter fibers that are less effective in strengthening the material
  • Fibers are cheaper, can be high I tensile strength and are easy to fabricate
• Random (chopped fibers): strength is not as high as aligned fibers but the material is cheaper
• Woven: woven into fabric and layered with a matrix material

Particles Reinforcement

• Consist of particles of one material dispersed in a matrix of a second material
• Particulate reinforced materials are not directional like fibers, they spread randomly to reinforce in all directions
• Added to a liquid matrix that later turns solid
• Use for wear resistance situations such as road surface
• Advantages include: Low cost, High stiffness and strength, Wear resistance, Simple manufacturing

Reasons to use Composite Materials

• Light weight
• Corrosion resistance
• Durable
• Low cost
• Heat resistance
• Design flexibility
• Electrical insulation

Application of Composite Materials By Area

• Aerospace benefits from strength and lightweight capabilities using Thermoset composites for wings and fuselages
• Transportation uses them to make vehicles lighter and more fuel efficient
• Civil infrastructure uses them to construct and repair infrastructure like Roads, buildings and bridges
• Construction is used because of high strength, light weight and resistance to corrosion properties. Thermoset composites are used for wall panels, doors and fixtures
• Marine uses corrosion resistant and light-weighing properties. Used for boat hulls