Lecture 9Lecture 9 Composite Material and

Processes

COMPOSITE MATERIALS Composite materials are polymers that have been

reinforced with organic or in-organic fiber materials (Fiber-reinforced polymers, FRPs).

The principal advantage of these materials is the very high strength-to-weight ratio, lightweight and strong, tailor made product which makes them attractive in aircrafts, spacecrafts, cars, boats, and sport equipment.

Starting materialsFiber-reinforced polymers consist of two components, polymer matrix and reinforced phase. They are produced separately before being combined to make the composite part.

Thermoplastics, thermosets or elastomers are used for the polymer matrix. Thermosetting polymers are the most common matrix materials, especially epoxies.

Reinforcing components Reinforcing components are fibers, cloth (fabrics), and mat of glass,

boron, carbon (graphite), polymers.

Fibers are used in some fabrication processes in a continuous form, known as roving, which is a collection of untwisted continuous threads. Each thread consists of 1000~30 000 single fibers.

Cloth is a fabric of woven yarns. Some special cloths can consists of different fibers, for example carbon + glass fibers:

Mat is a material that consists of randomly oriented short fibers.

In some applications, raw materials are combined prior to the shaping operations (the resulting material is known as a prepreg). The typical thickness of the prepreg is 0.125 mm with 34% polymer resin.

Shaping processesOpen mold process

Open mold processOpen mold process

Open mold processOpen mold process

Close mold processClose mold processIn these processes, molds consist of two sections that open and close during each molding cycle. In compression molding processes, starting materials are placed in the lower mold section, and the mold is closed under pressure. Next, the mold is heated to cure the polymer matrix. After curing, the mold is opened and the part is removed. Different compression molding processes were developed for different starting materials.

Filament winding

In this process, resin-impregnated fibers are wrapped around a rotating mandrel that has the internal shape of the desired Fiberglass Reinforced Plastic (FRP) part

Filament WindingFilament Winding

Filament WindingFilament Winding

PultrusionPultrusion

(a) Schematic illustration of the pultrusion process. (b) Examples of parts made by pultrusion.

The process is similar to extrusion, but it involves pulling of the workpiece. Pultrusion process is used to produce simple shapes of uniform cross section, such as round, rectangular, tubular, and structural products. The bundles of fibers are drawn through a bath of polymer resin and then gathered to produce a desired cross-sectional product. The material is then drawn through one or more heated dies for further shaping and curing. After cooling, material is cut to length

(b)

The major components of fiberglass The major components of fiberglass ladders (used especially by electricians) ladders (used especially by electricians) are made by this process. Unlike are made by this process. Unlike aluminum ladders, they are available in aluminum ladders, they are available in different colors but are heavier because of different colors but are heavier because of the presence of glass fibers.the presence of glass fibers.