1. Reinforcements

2. Reinforcements
A reinforcement is the strong, stiff integral component of a composite which is incorporated into the matrix to achieve desired properties.
The term ‘reinforcement’ implies some property enhancement

3. Forms of Reinforcements
Fibers
Discontinuous fibres: L/D ratio<100
Continuous fiber
cross-section can be circular, square or hexagonal
Textile Structure
Unidirectional
Woven
Braid
Particulate
Particles
Flakes

4. Materials for Fibres Glass – most widely used filament
Carbon – high elastic modulus
Boron – very high elastic modulus
Polymers - Kevlar
Ceramics – SiC and Al2O3
Metals - steel

5. Composite Parameters For a given matrix/dispersed phase system:
Concentration
Size
Shape
Distribution
Orientation

6. Parameters
Distribution
Concentration
Orientation
Shape
Size

7. Particles and Flakes
A second common shape of imbedded phase is particulate, ranging in size from nanoscopic to macroscopic
In most of the cases, the distribution of particles in the composite matrix is random, and therefore strength and other properties of the composite material are usually isotropic.

8. Parameters Size Shape （aspect ratio） Concentration Dispersion
Orientation
Isotropic or anisotropic？

9. Particle-carbon black

10. Flake-graphite nanoplatelet
Flakes are basically two‑dimensional particles

11. Nano-size, 2D oriented-graphene

12. Types of Fibers The fibers are divided into two main groups:
Glass fibers: There are many different kinds of glass, ranging from ordinary bottle glass to high purity quartz glass. All of these glasses can be made into fibers. Each offers its own set of properties.
Advanced fibers: These materials offer high strength and high stiffness at low weight. Boron, silicon, carbide and graphite fibers are in this category. So are the aramids, a group of plastic fibers of the polyamide (nylon) family.

13. Fibers - Glass Most widely used fiber
Applications: piping, tanks, boats, sporting goods
Fiberglass properties vary somewhat according to the type of glass used. However, glass in general has several well–known properties that contribute to its great usefulness as a reinforcing agent:
Tensile strength
Chemical resistance
Moisture resistance
Thermal properties
Electrical properties
Low cost
Disadvantages
Relatively low strength
High elongation
Moderate strength and weight

14. Fibers - Glass There are three main types of glass used in fiberglass:
E-glass: Most common glass used for reinforcement, especially for PCB laminates of electronic applications. High strength and good resistance to chemical attach
C-glass: Formulated for greater chemical corrosion resistance
S-glass: Stiffer (20% higher modulus) and stronger formulation for structural composite application. Higher creep rupture resistance and higher temperature application. Contain a higher alumina content and are most difficult to process-hence most costly

15. Fibers - Glass Glass structure
Three-dimensional polyhedral network containing oxygen atoms around a silicon atom with strong covalent bonds.
Molecular structure of glass

16. Fibers - Glass
Format
Fibre diameter: this may be varied between 10-20mm. Finer filaments give better properties, but uneconomical to produce fibres of less than 10mm.
Fibres are produced in bundles or strands which are treated with size as they are drawn. Several strands are put together to form roving.

17. Fibers - Glass Fibre Production Surface treatment
Glasses are produced from minerals (sand, lime, borax, etc.) based on silica (SiO2) with addition of oxides of Ca, B, Na, Fe, Al.
Continuous drawing from molten glass at high speed (~100m/s) through holes in a platinum alloy bushing
Surface treatment
To protect glass fibres from abrasion and mechanical damage, fibres are treated with water-based size immediately after forming.
For glass fibres intended for subsequently textile operation such as weaving, spooling, the size contain a mixture of starch and lubricant. The size also contain a coupling agent to improve adhesion with polymer resin.

19. Fibers – Aramid (Kevlar)
Applications:
High performance replacement for glass fiber
Aerospace and military applications
Examples：Armor, bullet vest, protective clothing, sporting goods
Advantages:
Higher strength and lighter than glass
More ductile than carbon
High use temperature compared to other organic fibres
High chemical resistance

20. Fibers – Aramid Fibre Production
Poly-phenylene-terephtahlamide (PPTA) is prepared by a condensation polymerisation of exact ratio of phenylenediamine with terephthaloyl chloride
The PPTA fibres are extruded at about 80°C in the form of liquid-crystalline PPTA-H2SO4 dopes from a spinneret
The resulting yarn is washed with water, neutralised with NaOH, subsequently dried under tension on rollers at °C (Kevlar 29)
Further drawing at 550 ° C for 1-6 sec produces yarns of higher modulus (Kevlar 49)

21. Fibers – Aramid

22. Fibers – Aramid Fibre Structure
The molecules form a planar array with weak interchain hydrogen bonding: easily fibrillated upon fracture
Radially arranged axially pleated crystalline supramolecular sheets