Fibre-reinforced plastic
Fibre-reinforced plastic is a composite material made of a polymer matrix reinforced with fibres. The fibres are usually glass, carbon, aramid, or basalt. Rarely, other fibres such as paper, wood, boron, or asbestos have been used. The polymer is usually an epoxy, vinyl ester, or polyester thermosetting plastic, though phenol formaldehyde resins are still in use.
FRPs are commonly used in the aerospace, automotive, marine, and construction industries. They are commonly found in ballistic armour and cylinders for self-contained breathing apparatuses.
History
was the first fibre-reinforced plastic. Leo Baekeland had originally set out to find a replacement for shellac. Chemists had begun to recognise 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 : bakelite. He announced his invention at a meeting of the American Chemical Society on 5 February 1909.The development of fibre-reinforced plastic for commercial use was being extensively researched in the 1930s. In the United Kingdom, considerable research was undertaken by pioneers such as Norman de Bruyne. It was particularly of interest to the aviation industry.
Mass production of glass strands was discovered in 1932, when Games Slayter, a researcher at Owens-Illinois accidentally directed a jet of compressed air at a stream of molten glass and produced fibres. A patent for this method of producing glass wool was first applied for in 1933.
Owens joined with the Corning company in 1935 and the method was adapted by Owens Corning to produce its patented "fibreglas" in 1936. 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. The first ancestor of modern polyester resins is Cyanamid's resin of 1942. Peroxide curing systems were used by then. With the combination of fibreglas and resin the gas content of the material was replaced by plastic. 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. Confusingly, many glass fibre composites continued to be called "fibreglass" and the name was also used for the low-density glass wool product containing gas instead of plastic.
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. The first car to have a fibre-glass body was the 1946 Stout Scarab. Only one of this model was built. The Ford prototype of 1941 could have been the first plastic car, but there is some uncertainty around the materials used as it was destroyed shortly afterwards.
The first fibre-reinforced plastic plane was either the Fairchild F-46, first flown on 12 May 1937, or the Californian built Bennett Plastic Plane. A fibreglass fuselage was used on a modified Vultee BT-13A designated the XBT-16 based at Wright Field in late 1942. 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. A significant development in the tooling for GFRP components had been made by Republic Aviation Corporation in 1943.
Carbon fibre production began in the late 1950s and was used, though not widely in British industry until the early 1960s. Aramid fibres were being produced around this time also, appearing first under the trade name Nomex by DuPont. Today, each of these fibres is used widely in industry for any applications that require plastics with specific strength or elastic qualities. 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. These three continue to be the important categories of fibre used in FRP.
Global polymer production on the scale present today began in the mid 20th century, when low material and productions costs, new production technologies and new product categories, combined to make polymer production economical. The industry finally matured in the late 1970s, when world polymer production surpassed that of steel, making polymers the ubiquitous material that they are today. Fibre-reinforced plastics have been a significant aspect of this industry from the beginning.
Process definition
A polymer is generally manufactured by step-growth polymerisation or addition polymerisation. 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. Composite plastics refers to those types of plastics that result from bonding two or more homogeneous materials with different material properties to derive a final product with certain desired material and mechanical properties. Fibre-reinforced plastics are a category of composite plastics that specifically use fibre materials to mechanically enhance the strength and elasticity of plastics.The original plastic material without fibre reinforcement is known as the matrix or binding agent. The matrix is a tough but relatively weak plastic that is reinforced by stronger stiffer reinforcing filaments or fibres. The extent that strength and elasticity are enhanced in a fibre-reinforced plastic depends on the mechanical properties of both the fibre and matrix, their volume relative to one another, and the fibre length and orientation within the matrix. Reinforcement of the matrix occurs by definition when the FRP material exhibits increased strength or elasticity relative to the strength and elasticity of the matrix alone.
Process description
FRP involves two distinct processes, the first is the process whereby the fibrous material is manufactured and formed, the second is the process whereby fibrous materials are bonded with the matrix during moulding.Fibre
Manufacture of fibre fabric
Reinforcing Fibre is manufactured in both two-dimensional and three-dimensional orientations:- Two-dimensional fibre glass-reinforced polymer is characterised by a laminated structure in which the fibres are only aligned along the plane in x-direction, and y-direction of the material. This means that no fibres are aligned in the through-thickness or the z-direction, this lack of alignment in the through thickness can create a disadvantage in cost and processing. Costs and labour increase because conventional processing techniques used to fabricate composites, such as wet hand lay-up, autoclave and resin transfer moulding, require a high amount of skilled labour to cut, stack and consolidate into a preformed component.
- Three-dimensional fibreglass-reinforced polymer composites are materials with three-dimensional fibre structures that incorporate fibres in the x-direction, y-direction and z-direction. The development of three-dimensional orientations arose from industry's need to reduce fabrication costs, to increase through-thickness mechanical properties, and to improve impact damage tolerance; all were problems associated with two-dimensional fibre-reinforced polymers.
Manufacture of fibre preforms
- Weaving can be done in a conventional manner to produce two-dimensional fibres as well as in a multilayer weaving that can create three-dimensional fibres. However, multilayer weaving requires multiple layers of warp yarns to create fibres in the z-direction, creating a few disadvantages in manufacturing, namely the time to set up all the warp yarns on the loom. Therefore, most multilayer weaving is currently used to produce relatively narrow width products, or high value products where the cost of the preform production is acceptable. Another one of the main problems facing the use of multilayer woven fabrics is the difficulty in producing a fabric that contains fibres oriented at other than right angles to each other.
- The second major way of manufacturing fibre preforms is Braiding. Braiding is suited to the manufacture of narrow width flat or tubular fabric and is not as capable as weaving in the production of large volumes of wide fabrics. Braiding is done over top of mandrels that vary in cross-sectional shape or dimension along their length. Braiding is limited to objects about a brick in size. Unlike standard weaving, braiding can produce fabric that contains fibres at 45-degree angles to one another. Braiding three-dimensional fibres can be done using four-step, two-step or Multilayer Interlock Braiding. Four-step or row and column braiding utilises a flat bed containing rows and columns of yarn carriers that form the shape of the desired preform. Additional carriers are added to the outside of the array, the precise location and quantity of which depends upon the exact preform shape and structure required. There are four separate sequences of row and column motion, which act to interlock the yarns and produce the braided preform. The yarns are mechanically forced into the structure between each step to consolidate the structure, as a reed is used in weaving. Two-step braiding is unlike the four-step process because the two-step process includes a large number of yarns fixed in the axial direction and a lesser number of braiding yarns. The process consists of two steps in which the braiding carriers move completely through the structure between the axial carriers. This relatively simple sequence of motions is capable of forming preforms of essentially any shape, including circular and hollow shapes. Unlike the four-step process, the two-step process does not require mechanical compaction: the motions involved in the process allows the braid to be pulled tight by yarn tension alone. The last type of braiding is multi-layer interlocking braiding that consists of a number of standard circular braiders being joined to form a cylindrical braiding frame. This frame has a number of parallel braiding tracks around the circumference of the cylinder but the mechanism allows the transfer of yarn carriers between adjacent tracks forming a multilayer braided fabric with yarns interlocking to adjacent layers. The multilayer interlock braid differs from both the four-step and two-step braids in that the interlocking yarns are primarily in the plane of the structure and thus do not significantly reduce the in-plane properties of the preform. The four-step and two-step processes produce a greater degree of interlinking as the braiding yarns travel through the thickness of the preform, but therefore contribute less to the in-plane performance of the preform. A disadvantage of the multilayer interlock equipment is that due to the conventional sinusoidal movement of the yarn carriers to form the preform, the equipment is not able to have the density of yarn carriers that is possible with the two-step and four-step machines.
- Knitting fibre preforms can be done with the traditional methods of Warp and Knitting, and the fabric produced is often regarded by many as two-dimensional fabric, but machines with two or more needle beds are capable of producing multilayer fabrics with yarns that traverse between the layers. Developments in electronic controls for needle selection and knit loop transfer, and in the sophisticated mechanisms that allow specific areas of the fabric to be held and their movement controlled, have allowed the fabric to be formed into the required three-dimensional preform shape with a minimum of material wastage.
- Stitching is arguably the simplest of the four main textile manufacturing techniques and one that can be performed with the smallest investment in specialised machinery. Basically stitching consists of inserting a needle, carrying the stitch thread, through a stack of fabric layers to form a 3D structure. The advantages of stitching are that it is possible to stitch both dry and prepreg fabric, although the tackiness of the prepreg makes the process difficult and generally creates more damage within the prepreg material than in the dry fabric. Stitching also utilises the standard two-dimensional fabrics that are commonly in use within the composite industry, so there is a sense of familiarity with the material systems. The use of standard fabric also allows a greater degree of flexibility in the fabric lay-up of the component than is possible with the other textile processes, which have restrictions on the fibre orientations that can be produced.