Fiber Reinforced Polymer Composities

Fiber Reinforced Polymer composities: 

A composite material is defined as a macroscopic combination of two or more distinct components.  It includes a discontinuous reinforcement (fibers or particles) phase and continuous matrix phase (binder or resin).

Classification of composities:

Composite material is a material composed of two or more distinct phases (matrix phase and dispersed phase) and having bulk properties significantly different form those of any of the constituents. 

Matrix phase:

The primary phase, having a continuous character, is called matrix. Matrix is usually more ductile and less hard phase. It holds the dispersed phase and shares a load with it. 

Dispersed (reinforcing) phase:

The second phase (or phases) is imbedded in the matrix in a discontinuous form. This secondary phase is called dispersed phase. Dispersed phase is usually stronger than the matrix, therefore it is sometimes called reinforcing phase. 

Many of common materials (metal alloys, doped Ceramics and Polymers mixed with additives) also have a small amount of dispersed phases in their structures, however they are not considered as composite materials since their properties are similar to those of their base constituents (physical properties of steel are similar to those of pure iron). 

There are two classification systems of composite materials. One of them is based on the matrix material (metal, ceramic, and polymer) and the second is based on the material structure: 

1. Classification of composites I (Matrix Material Base) 

Metal Matrix Composites (MMC):

Metal Matrix Composites are composed of a metallic matrix (aluminum, magnesium, iron, cobalt, copper) and a dispersed ceramic (oxides, carbides) or metallic (lead, tungsten, molybdenum) phase. 

Ceramic Matrix Composites (CMC):

Ceramic Matrix Composites are composed of a ceramic matrix and imbedded fibers of other ceramic material (dispersed phase). 

Polymer Matrix Composites (PMC):

Polymer Matrix Composites are composed of a matrix from thermoset (Unsaturated Polyester (UP), Epoxy (EP)) or thermoplastic, (Polycarbonate (PC), Polyvinylchloride, Nylon, Polysterene) and embedded glass, carbon, steel or Kevlar fibers (dispersed phase). 

2. Classification of Composite Materials II (Material Structure Base) 

1. Particulate Composites:

Particulate Composites consist of a matrix reinforced by a dispersed phase in form of particles. 

1. Composites with random orientation of particles.

2. Composites with preferred orientation of particles

Dispersed phase of these materials consists of two-dimensional flat platelets (flakes), laid parallel to each other.

2. Fiber Reinforced Composites (FRP)

Fiber Reinforced Polymer (FRP) Composites are defined as “A matrix of polymeric material that is reinforced by fibbers or other reinforcing material”

3. Short-fiber reinforced composites. Short-fiber reinforced composites consist of a matrix reinforced by a dispersed phase in form of discontinuous fibbers.

4. Composites with random orientation of fibbers.

5. Composites with preferred orientation of fibbers.

1. Long-fiber reinforced composites. Long-fiber reinforced composites consist of a matrix reinforced by a dispersed phase in form of continuous fibbers.

1. Unidirectional orientation of fibbers.

2. Bidirectional orientation of fibbers (woven).

Laminate Composites

2. When a fiber reinforced composite consists of several layers with different fiber orientations, it is called multilayer (angle-ply) composite.

FRP COMPOSITE CONSTITUENTS

1. Resins (Polymers)

2. Reinforcements

3. Fillers

4. Additives

Material: Resins

Primary Function: Transfer stress between reinforcing fibers and to protect them from mechanical and environmental damage.

Types: 

Thermoset: Polyester, Vinyl ester, Epoxy, Phenolic, Polyurethane etc.

Thermoplastic: Acetal, Acryronitrile Butadiene Styrene (ABS), Nylon, Polyethylene (PE), Polypropylene (PP), Polyethylene Terephthalate (PET) etc.

Material: Fiber Reinforcements

1. Primary Function: Carry load along the length of the fiber, provides strength and or stiffness in one direction.

2. Can be oriented to provide properties in directions of primary loads

Reinforcements

1. Natural 

2. Man-made

3. Many varieties commercially available

PROCESSING OF FRP

There are two general divisions of composites manufacturing processes: open moulding (sometimes called contact moulding) and closed moulding. 

In open moulding, the gel coat and laminate are exposed to the atmosphere during the fabrication process. 

In closed moulding, the composite is processed in a two-sided mould set, or within a vacuum bag. There are a variety of processing methods within the open and closed moulding categories: 

OPEN MOULD FABRICATION OF POLYMER MATRIX COMPOSITES

1. HAND LAY-UP METHOD

Process

The Hand Lay-up involves the following operations: 

1. The mould is coated by a release anti-adhesive agent, preventing sticking the moulded part to the mould surface.

2. The prime surface layer of the part is formed by applying gel coating.

3. A layer of fine fiber reinforcing tissue is applied.

4. Layers of the liquid matrix resin and reinforcing fibbers in form of woven fabric, rovings or chopped strands are applied. The resin mixture may be applied by either brush or roll.

5. The part is cured (usually at room temperature).

6. The part is removed from the mould surface.

There are two methods of Hand Lay-up:

Wet Lay-up:

1. Dry reinforcement (fiber mat or woven cloths) is first applied to the mould, and then is saturated with liquid resin

Dry Lay-up:

1. Reinforcement and resin (thermoset) are applied simultaneously as a pre-impregnated fiber tape (prepreg) 

2. The resin in the prepreg sheets is ‘B’ staged (i.e. solidified and tacky but only partially cured)

Advantages

1. Simplest method offering low-cost tooling, simple processing and a wide range of part sizes. 

2. Design changes are readily made. 

3. There is a minimum investment in equipment. 

4. With skilled operators, good production rates and consistent quality are obtainable. 

Disadvantages

1. Low concentration of reinforcing phase (up to 30%) 

2. Low densification of the composites (entrapped air bubbles)

3. Labour intensive

4. Difficult to control the hand laminating process

Application

Boats, tanks, bathware, housings, RV/truck/auto components, architectural products, and many other products ranging from very small to very large. using multiple moulds.

2. SPRAY-UP METHOD

Spray-up is an open-moulding composites fabrication process where resin and reinforcements are sprayed onto a mould. The resin and glass may be applied separately or simultaneously "chopped" in a combined stream from a chopper gun.

Procerss

1. As with hand lay-up, gel coat is first applied to the mould prior to spray-up of the substrate laminate. 

2. Continuous strand glass roving and catalyzed resin are fed through a chopper gun which deposits the resin-saturated "chop" on the mould. 

3. The laminate is then rolled to thoroughly saturate the glass strands and compact the chop. Additional layers of chop laminate are added as required for thickness. 

4. Roll stock reinforcements such as woven roving or knitted fabrics, can be used in conjunction with the chopped laminates. 

5. Core materials of the same variety as used in hand lay-up are easily incorporated

Advantages 

1. Permits rapid formation of uniform composite coating

2. Low-cost tooling, 

3. Simple processing; 

4. Portable equipment permits on-site fabrication; 

5. The process may be automated. 

Disadvantage

1. Mechanical properties of the material are moderate since the method is unable to use continuous reinforcing fibers.

2. In the spray-up process the operator controls thickness and consistency. Therefore the process is more operator dependent than hand lay-up.

3. Production volume per mould is low. 

4. Produces short fiber reinforcement (low strength applications)

5. Spray area requires necessary ventilation

Application

Boats, tanks, transportation components and tub/shower units in a large variety of shapes and sizes.

3. FILAMENT WINDING

Filament winding is an automated open moulding process that uses a rotating mandrel as the mould. The male mould configuration produces a finished inner surface and a laminate surface on the outside diameter of the product. 

There are two types of Filament winding:

1. If a liquid thermosetting resin is applied on the filament prior to winding, the process is called Wet Filament Winding. 

2. If the resin is sprayed onto the mandrel with wound filament, the process is called Dry Filament Winding. 

Process 

1. Continuous strand roving is fed through a resin bath and wound onto a rotating mandrel. 

2. The roving feed runs on a trolley that traverses the length of the mandrel. 

3. The filament is laid down in a predetermined geometric pattern to provide maximum strength in the directions required. 

4. When sufficient layers have been applied, the laminate is cured on the mandrel. The moulded part is then stripped from the mandrel. 

5. Filament winding can be combined with the chopping process and is known as the hoop chop process. 

Advantages

1. The process makes the high strength-to-weight ratio laminates

2. Provides high degree of control over uniformity and fiber orientation 

3. Relatively fast process (automated)

4. Labor factor for filament winding is lower than other open moulding processes. 

5. Produce parts with complex profiles along its length and irregular cross-sectional shapes (e.g. rectangular tubing)

Disadvantages

1. Expensive and complex machinery required (extensive capital investment)

2. Difficult to wind angles along mandrel axis

Application

Cylindrical products such as chemical and fuel storage tanks, pipes, stacks, pressure vessels, and rocket motor cases.

4. Tape Lay-up

In this method layers of prepreg (reinforcing phase impregnated by liquid resin) tape are applied on the mold surface by a tape application robot.

5. Autoclave Curing

1. Autoclave Curing is a method in which a part, molded by one of the open molding methods, is cured by a subsequent application of vacuum, heat and inert gas pressure.

2. The molded part is first placed into a plastic bag, from which air is exhausted by a vacuum pump. This operation removes air inclusions and volatile products from the molded part.

3. Then heat and inert gas pressure are applied in the autoclave causing curing and densification of the material.

4. Autoclave Curing enables fabrication of consistent homogeneous materials. The method is relatively expensive and is used for manufacturing high quality aerospace products.

CLOSED MOULD FABRICATION OF POLYMER MATRIX COMPOSITES

Closed Mould methods are used when mass production of identical parts with both smooth surfaces is required.

1. COMPRESSION MOULDING

2. INJECTION MOULDING

3. TRANSFER MOULDING

4. PULTRUSION