Fibre-reinforced plastic
Chemists had begun to recognize that many natural resins and fibres were polymers, and Baekeland investigated the reactions of phenol and formaldehyde.
He first produced a soluble phenol-formaldehyde shellac called "Novolak" that never became a market success, then turned to developing a binder for asbestos which, at that time, was moulded with rubber.
By controlling the pressure and temperature applied to phenol and formaldehyde, he found in 1905 he could produce his dreamed of hard mouldable material (the world's first synthetic plastic): bakelite.
Originally, fibreglas was a glass wool with fibres entrapping a great deal of gas, making it useful as an insulator, especially at high temperatures.
A suitable resin for combining the "fibreglas" with a plastic to produce a composite material, was developed in 1936 by du Pont.
This reduced the insulation properties to values typical of the plastic, but now for the first time the composite showed great strength and promise as a structural and building material.
Ray Greene of Owens Corning is credited with producing the first composite boat in 1937, but did not proceed further at the time due to the brittle nature of the plastic used.
In 1939, Russia was reported to have constructed a passenger boat of plastic materials, and the United States a fuselage and wings of an aircraft.
[12] In 1943, further experiments were undertaken building structural aircraft parts from composite materials resulting in the first plane, a Vultee BT-15, with a GFRP fuselage, designated the XBT-19, being flown in 1944.
Glass fibres are the most common across all industries, although carbon-fibre and carbon-fibre-aramid composites are widely found in aerospace, automotive and sporting good applications.
When one or more polymers are combined with various agents to enhance or in any way alter their material properties, the result is referred to as a plastic.
The four major ways to manufacture the fibre preform is through the textile processing techniques of weaving, knitting, braiding and stitching.
This is a very common process in the aerospace industry because it affords precise control over moulding due to a long, slow cure cycle that is anywhere from one to several hours.
The impregnated chopped glass is shot onto the mould surface in whatever thickness and design the human operator thinks is appropriate.
[20] Machines pull fibre bundles through a wet bath of resin and wound over a rotating steel mandrel in specific orientations.
[20] Fibre bundles and slit fabrics are pulled through a wet bath of resin and formed into the rough part shape.
These materials can be used to create all sorts of fibreglass structures such as ladders, platforms, handrail systems tank, pipe and pump supports.
The matrix must be able to properly saturate, and preferably bond chemically with the fibre reinforcement for maximum adhesion within a suitable curing period.
These mixtures are then heated through direct melting to temperatures around 1300 degrees Celsius, after which dies are used to extrude filaments of glass fibre in diameter ranging from 9 to 17 μm.
[17] Further production processes include weaving or braiding into carbon fabrics, cloths and mats analogous to those described for glass that can then be used in actual reinforcements.
FRP composites have a wide range of applications across various industries due to their unique combination of properties, including high strength-to-weight ratio, corrosion resistance, and design flexibility.
Principal tensile fibres are oriented parallel to the beam's longitudinal axis, similar to its internal flexural steel reinforcement.
It provides the least amount of shear strengthening due to failures caused by de-bonding from the concrete surface at the FRP free edges.
Closed wrapping involves applying FRP around the entire perimeter of the member, such that there are no free ends and the typical failure mode is rupture of the fibres.
For all wrap configurations, the FRP can be applied along the length of the member as a continuous sheet or as discrete strips, having a predefined minimum width and spacing.
[29] FRP is used in designs that require a measure of strength or modulus of elasticity for which non-reinforced plastics and other material choices are ill-suited, either mechanically or economically.
The primary design consideration for using FRP is to ensure that the material is used economically and in a manner that takes advantage of its specific structural characteristics, but this is not always the case.
The properties of strength, flexibility and elasticity can also be magnified or diminished through the geometric shape and design of the final product.
For example, ensuring proper wall thickness and creating multifunctional geometric shapes that can be moulded as a single piece enhances the material and structural integrity of the product by reducing the requirements for joints, connections, and hardware.
[30] In addition to concerns regarding safe disposal, the fact that the fibres themselves are difficult to remove from the matrix and preserve for re-use means FRP's amplify these challenges.
