Fibre-reinforced plastic

Fiber Reinforced Plastic

A composite material consisting of a polymer matrix enhanced with fibers.

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Fiber Reinforced Plastic (FRP, also known as Fiber Reinforced Polymer), refers to a composite material which combines a polymer matrix with a reinforcement of fibers. These fibers typically comprise glass (in the case of fiberglass), carbon (in carbon-fiber-reinforced polymer), aramid, or basalt. In some niche applications, fibers made from paper, wood, boron, or even asbestos can be utilized. The polymer used is generally either epoxy, vinyl ester, or thermosetting polyester, although phenol formaldehyde resins are still sometimes employed.

FRPs have gained significant traction across various sectors, including aerospace, automotive, marine, and construction. You might encounter them frequently in ballistic armor and in cylinders for self-contained breathing apparatuses.

History

The inception of fiber-reinforced plastic can be traced back to Bakelite, which was the pioneering example of such materials. Inventor Leo Baekeland aimed to create a substitute for shellac, derived from shellac bugs’ excretion. As chemists identified the polymeric nature of many natural resins and fibers, Baekeland explored the reactions of phenol and formaldehyde, initially producing a soluble phenol-formaldehyde shellac called "Novolak". This product, however, did not find market success. He later endeavored to formulate a binder for asbestos, which was then molded alongside rubber. By meticulously adjusting the pressure and temperature during the phenol and formaldehyde reaction, he successfully produced Bakelite, the world’s first synthetic plastic.

During the mid-20th century, extensive research and development into fiber-reinforced plastics for commercial use was undertaken. Notably, in the UK, work was driven by pioneers such as Norman de Bruyne, with particular interest from the aviation sector.

In a groundbreaking moment in 1932, researcher Games Slayter from Owens-Illinois stumbled upon a technique to mass-produce glass strands. His method, which involved directing compressed air at molten glass, paved the way for modern glass wool production. Subsequent advancements led to the creation of fiberglass, which began in 1938. The introduction of a suitable resin to bind fiberglass with plastics came in 1943, resulting in a composite material with structural integrity and foundational strength.

Today, FRPs have diversified into several fiber categories, including glass, carbon, and aramid, each serving various industrial applications. Their production technology has matured, with polymer production now surpassing steel worldwide and establishing fiber-reinforced plastics as fundamental components of modern manufacturing.

Process Definition

Typically, the manufacturing process of polymers follows step-growth polymerization or addition polymerization. When combined with various agents to enhance their properties, they become classified as plastics. Specifically, fiber-reinforced plastics refer to those composites that utilize fiber materials for mechanical strength enhancement.

The primary composite plastic matrix is usually robust yet relatively weak. Strength and elasticity improvements in fiber-reinforced plastics hinge on the interaction between the fiber and matrix’s mechanical properties, their volumetric ratio, and the fibers' orientation and length.

Process Description

Production of FRP involves two core processes: the creation of fibrous material and the subsequent bonding of these fibers with the polymer matrix during the molding process.

Fiber

Manufacture of Fiber Fabric

Reinforcing fibers are produced in two-dimensional and three-dimensional forms:

1. Two-dimensional fiberglass-reinforced plastics possess a laminated form where fibers are solely aligned across the material's plane (x and y directions). This configuration lacks fibers in the thickness dimension (z-direction), which can complicate processing and increase costs, as higher labor is required for fabrication tasks.
2. Three-dimensional fiberglass-reinforced composites incorporate three-dimensional structures with fibers in all directions (x, y, and z). This innovation addresses cost and performance limitations faced by two-dimensional variants.

Manufacture of Fiber Preforms

Fiber preforms, manufactured as sheets or continuous mats, form the basis for bonding with the polymer matrix. The main fabrication approaches include weaving, knitting, braiding, and stitching.

1. Weaving—both conventional and multi-layer weaving for two- or three-dimensional fibers.
2. Braiding—which can produce narrow materials and allows for 45-degree fiber orientations.
3. Knitting—utilizes traditional methods to create multilayer fabrics, enabling greater design flexibility.
4. Stitching—considered the simplest method; it allows processing of both dry and prepreg materials.

Forming Processes

FRP components are typically molded using various techniques, commonly encompassing a rigid structure for outline formation. Most parts are produced using molds that can range from male and female to fully encapsulating designs.

Methods of forming include:

Bladder Moulding

Involves prepreg sheets and a balloon-like bladder within a closed mold subjected to heat and pressure.

Compression Moulding

A process where fiber-containing materials are heated and pressed into shapes.

Autoclave and Vacuum Bag

Prepreg layers in an open mold undergo vacuum treatment and are cured under controlled conditions.

Wet Layup

This technique combines fibers and resin directly on a mold, typically resulting in fiberglass products.

Chopper Gun

Automates the application of chopped fiberglass and resin onto molds for large-scale production.

Resin Transfer Moulding

Employs a vacuum to inject resin into molds containing fabric, allowing for precise shaping.

Advantages and Limitations

FRP materials enable tailored fiber orientation, enhancing structural strength and resistance to deformation. However, this creates inherent limitations in specific applications, particularly with weakness in perpendicular fiber orientations. Developing multi-dimensional fiber structures aids in mitigating these weaknesses.

Applications

Fiber reinforced plastics find usage across multiple sectors, given their exceptional strength-to-weight ratios and durability. Common materials include:

• Glass Fiber Reinforced Polymers: Cost-effective with considerable tensile strength.
• Carbon Fiber Reinforced Polymers: Known for superior strength and stiffness.
• Aramid Fiber Reinforced Polymers: Employed in military and high-performance settings.
• Natural Fiber Reinforced Polymers: Eco-friendly options derived from renewable resources.

Repeat applications inclusively extend to aerospace, automotive, marine, and the construction of components within the oil and gas industries.

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