Composites
- 1. COMPOSITES 1
- 2. Composites • Composites are the engineered materials which can satisfy the requirements of modern technology as they have several advantageous features such as High specific strength (ratio of tensile strength to density) High specific modulus (ratio of modulus of elasticity to density) High strength to weight ratio (low density high tensile strength) High tensile strength at elevated temperatures High toughness 2
- 3. Composites Definition: • Composites are combinations of Two or more chemically distinct materials which when combined have improved properties over the individual materials. • One of the material is called the reinforcing phase, is in the form of fibers, sheets, or particles, and is embedded in the other material called the matrix phase. 3
- 4. Composites could be natural or synthetic. • Wood is a good example of a natural composite, combination of cellulose fiber and lignin. – The cellulose fiber provides strength and the lignin is the "glue" that bonds and stabilizes the fiber. • Bamboo is a very efficient wood composite structure. The components are cellulose and lignin, as in all other wood, however bamboo is hollow. – This results in a very light yet stiff structure. • The combination of mud and straw forms a composite that is stronger than either the mud or the straw by itself Composites 4
- 5. • The composite brick consisting of pieces of straw embedded in a block of mud on drying exhibits both compressive and tensile strength and hence makes a good building material • Another e.g. of a composite is concrete consisting of aggregate (small stones or gravel) bound by cement – Concrete has good strength under compression and its strength under tension can be improved by embedding metal rods making it reinforced concrete. Composites 5
- 6. 6 • Typically, reinforcing materials are strong with low densities while the matrix is usually a ductile or tough material. • If the composite is designed and fabricated correctly, it combines the strength of the reinforcement with the toughness of the matrix to achieve a combination of desirable properties not available in any single conventional material. Reinforcement: fibers Glass fibre Carbon, Metallic rods Matrix materials Polymers Metals Ceramics Components of composite materials Composites
- 7. 7 CLASSIFICATION OF COMPOSITES May be classified on the basis of reinforcement and the strengthening mechanism into three main types which include 1. Particle reinforced composites 2. Fibre reinforced composites • Continuous fibers, unidirectionally aligned • Discontinuous fibers, unidirectionally aligned • Discontinuous fibers, randomly aligned 3. Structural composites Composites
- 8. 8 1. Particle reinforced composites Aligned, discontinuous Random, Discontinuous 2. Fiber reinforced composites Continuous fiber 1.Struct ural comp osites 3. Structural composites
- 10. Particle Reinforced composites 10 May be sub-classified into two types: 1. Large particle composites and 2. Dispersion strengthen composites
- 11. Large particle composites(Particle Reinforced composites) 11 Consist of a high volume fraction of large sized hard particles embedded in a relatively soft matrix. The matrix and reinforcing particle share the load. Large particle composites may involve metals, polymers (plastics) and ceramics as matrices.
- 12. Examples: Large particle composites Concrete (cement with sand or gravel):cement is matrix, sand is particulate, Some polymers with added fillers Carbon black reinforced rubber is an example of polymer reinforced by particulate composites. Carbon black is added to rubber in a range of 15-30% by weight to improve the tensile strength, toughness and abrasion resistance of rubber used for manufacturing tyres 12
- 13. Large particle composites • Cermets are metal matrix composites containing ceramic particles • A typical e.g. of cermet is the cermet carbide made of extremely hard & refractory particles of ceramics such as WC or TiC embeded in a matrix of ductile metal such as cobalt or nickel – These composites find use as cutting tools for hardened steel Desired Characteristics • Particles should be evenly distributed 13
- 14. CERMET Cutting Tool Light phase - Matrix (Cobalt) Dark phase- Particulate (WC)
- 15. Dispersion strengthened composites 15 • Contain extremely small sized particles in the range of 10-100 nm • Dispersed in the matrix at low concentration which increase the particle matrix interactions at the atomic level thereby enhancing the strength of the matrix against deformation.
- 16. Dispersion strengthened composites 16 • The small particles hinder the migration of dislocations within the matrix thereby restricting the plastic deformation and increasing the tensile strength and hardness of the matrix
- 17. Dispersion strengthened composites 17 • Most of these composites involve metal matrix composites • Metal matrix composites of high strength can be improved by dispersing small particles of metal or metal oxides e.g. Thoria (3%) dispersed in nickel (TD Nickel) Al2O3 reinforced Al- sintered aluminum powder (SAP) • TD Nickel retains its strenth at high temperatures and ni doesn’t soften because of the dispersed microscopic thoria (ThO2) particles