List of Particle Reinforced Composites | Materials

Here is a list of particle reinforced composites: 1. Large Particle Composites 2. Cermet (Cer + met ≈ Ceramics + Metal) 3. Concrete 4. Reinforced Concrete.

1. Large Particle Composites:

Particles should be equiaxed. For effective reinforcement, the particles should be small and evenly distributed throughout the matrix.

Further, the mechanical properties are enhanced with increasing volume fraction of particles. Elastic modulus depends upon volume fraction of both phases. Hence particle is 1µm.

2. Cermet (Cer + met ≈ Ceramics + Metal):

Most common e.g. of particle reinforced composites. Most common cermets is cemented carbide, which is composed of extremely hard particles of carbide ceramic such as tungsten carbide or titanium carbide embedded in a matrix of a metal such as cobalt and Nickel.

These composite are extensively utilized as cutting tool for hardened steels.

The hard carbide particles provide the cutting surface but, being extremely brittle, are not themselves capable of withstanding the cutting stresses. Toughness is improved by their inclusion in metal matrix, which isolates the carbide particles from one another and prevents particle to particle crack propagation.

Relatively large volume fraction of the particulate phase may be utilized after exceeding 90% of volume, thus abrasive action of the composite is maximized.

3. Concrete:

(It is a ceramic-ceramic composite). Portland cement concrete is the most common example.

The ingredients of portland cement are, a fine aggregate (sand), a coarse aggregate (gravel) and water. Aggregate particles acts as a filler material to reduce the overall cost of the concrete products because they are cheap and cement is expensive.

Dense packing of aggregates and good interfacial contact are achieved by having particles of two different sizes i.e. the fine sand particles should fill the void spaces between gravel particles.

Aggregates account for 60-70% of the total volume.

The amount of cement water paste should be sufficient to coat all the sand and gravel particles, otherwise, excessive porosity.

Surface of the aggregates should be free from clay and slit in order to have a sound bond with cement. This concrete is a major structural material, get hardness at room temperature and even when submerged in water.

It also has some disadvantage as it is extremely brittle and its tensile strength is 10 to 15 times smaller than its compressive strength. Also large concrete structures experience considerable thermal expansion and contraction with temperature fluctuations.

In addition water penetrates into external pores, which may cause severe cracking in cold weather.

4. Reinforced Concrete:

The strength of portland concrete may be increased reinforcement by steel rods, wires, bars or mesh which are embedded into fresh and uncured concrete.

Thus reinforced structure is capable of supporting greater tensile, compressive and shear stresses. Even if cracks develop in concrete, considerable reinforcement is maintained.

Steel serves as a suitable reinforcement material because its coefficient of thermal expansion is nearly same as that of concrete. Also, steel is not rapidly corroded in cement environment and a relatively strong adhesive bond is formed between steel and concrete.

Another reinforcement technique for strengthening concrete is to introduce residual compressive stress into the structural member, the resulting material is called pre-stressed concrete.

In this process, high strength steel wires are positioned inside the empty moulds and allowed to harden, the tension is then released. Now the wires contract, and they put structure in a state of compression.

Another technique of inducing compressive stress is “tensioning”.

Sheet metal or rubber tubes are situated in concrete structure and is allowed to harden. The holes created are fed with steel wires.

Tension is applied to steel wires through Jacks, attached and abutted to the faces of structure. Again a compressive stress is imposed on concrete structure by the jacks.