Filament Windings

Filament winding involves winding rovings onto a mandrel. The rovings 

The principal data from other chapters are listed in Table 11.21. 

The hydrostatic strength decreases monotonically with time and is around 90 MPa after 10,000 hours. Cyclic loading has a greater effect and a strength of 50 MPa would be appropriate. 

For pressure loading of pipes, measurements are essential to determine the long-term strength retention as well as the likely mode of failure. Extrapolation by a factor of 10 is permissible under certain conditions (section 2.6) in order to establish the design allowable stress. 

This pipe system has been shown to provide excellent chemical resistance against many corrosive fluids encountered in the chemical process industry. 

Fibers can be arranged to traverse the mandrel at different angles with different winding frequencies in a programmed manner accomplished by automatic control or computer aided control. 

In this technique resin is poured onto a mold and a. small pressure is applied. Curing takes place at room temperature. 

The catalysed resin and the accelerated resin are kept in separate tanks, they can be mixed just before injection, or mixed in the injection gun. The applied pressure is around 450 kPa. This process has the advantage of producing objects free of air bubbles and damaged fibers. The air is removed by letting some resin flow out from the mold cavity. 

The FW mandrel must be strong enough to withstand rather high accumulated tension loads due to the filament winding, and must be stiff enough not to sag between end supports. At the same time, it must be possible to remove the mandrel from the finished part after curing, which may require the use of an intricate collapsible mandrel. 

As filaments are continuous and tightly packed, they permit a high fll-ament-to-resin ratio. This capability often results in products having the highest strength-to-weight ratio obtainable in any structures. 

Even though most FW uses glass filaments, all types of filaments can be used (Table 7-1). Precautions must be observed if superior properties are 

As explained in Chapter 2, most IM parts are made from TP, and some of the TP uses milled glass fibers to improve part performance. Other fibers have seen limited use to date. TS compounds usually include reinforcements. Details on IM and factors that influence machine and mold performance, such as wear and abrasion, are reviewed in Chapter 2. 

TS reinforced molding compounds processed in IM require water- or oil-cooled barrels, rather than the electrically heated barrels used for TP. The heat of the TS during screw plastication has to be kept lower than its curing heat. The mold heat is higher than that of the resin, causing the TS finally to react and solidify. If there is excess heat in the barrel, the resin crosslinks and the machine stops operating. A cleanup is required, which can cause machine downtime to be extensive. With a liquid heat control, better control of melt heat is maintained. Also the compression ratio of the screw used to process the TS is one, which helps to keep the heat low and, more important, under control. 

2 Fiber Motion Submodel Thermosetting Matrix Cylinders. 401 

Filament-wound structures are often used to store fluid under pressure fuel storage tanks, rocket motor cases, natural gas, and oxygen storage tanks. In some cases, the filament-wound structure is subjected to external pressure a diving bell or submarine. Filament winding has 

Although oven curing may be required, the cost of a large oven is significantly less than the cost of a similarly sized autoclave. 

Cylinders may be wound with a wet winding process while maintaining high fiber volume fractions typically seen in parts made from preimpregnated (B staged) materials. 

Obtaining desired fiber volume fraction requires precise control of winding conditions 

While prepreg processing provides high performance composites, it is expensive. Costs include  

As noted, autoclaves have to be large enough to accommodate components, and they need to process a number of components of uniform thickness to be both cost effective and ensure effective curing. The autoclave can often form a bottle-neck for composites manufacturing since commercial autoclaves are large and, to be viable, fiiU loads have to be assembled. Since components of similar thickness must be processed under the same cure cycle, good production scheduling is cmcial to the success of the operation. 

Many layers of the same or different patterns can be placed on the mandrel. The repeated patterns and reinforcement spacing are subject to close control. During winding, fibre tension generates pressure between layers of uncured composite. This pressure influences the compaction and void content of the article which in turn controls 

Angle of fibre warp controlled by ratio of carriage speed to rotation speed 

Most high performance applications in aircraft use epoxy-based resin systems. Silicones, phenolics and polyimides are limited to special high temperature or electrical applications. Although thermosetting resins such as epoxy are commonly used in filament winding, there has been recent research into using thermoplastic matrix materials [9]. 

Continuous fibre rovings are pulled through a bath of resin and are then wound on to a driven mandrel . With the arrangement shown, a tubular component results when the resin has hardened and the mandrel is 

9 Two processes for the forming of reinforced thermosets (a) pultrusion and (b) filament winding. 

1600°C was twice that at room temperature, thought to be due to the large thermal expansion coefficient of / BN in the b axis direction. 

The technique is more appropriate for a glass matrix, with its associate viscous flow when processed, since a surface excess of ceramic particles when coating a carbon fiber tow tends to persist in the fiber lay up. 

Vacuum infusion (resin infusion under flexible tooling, RIFT) 

The typical values of Vf, being the volume fraction of the fibers (ratio between the volume of the fibers and the overall volume of the composite), that can be obtained with this technology are 25-30 %. 

In a few cases, in order to improve the quality of the printed laminate, the impregnation of the fabrics is performed before laying them up, with ad hoc equipment so as to use the right quantity of resin for each foil, which allows to reach Vf values of 35-38 %. 

Even though this technique has been known for more than 30 years now, it has been profitably used only recently thanks to the introduction of reliable materials and devices which facilitated production and made it less expensive. Together with 

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Automated ultrasonic inspection of filament winded beams... 

The coin-tap test is a widely used teclinique on thin filament winded beams for detection of disbonded and delaminated areas. However, since the sensitivity of this teclinique depends not only on the operator but also on the thickness of the inspected component, the coin-tap testing technique is most sensitive to defects positioned near the surface of the laminate. Therefore, it was decided to constructed a new scaimer for automated ultrasonic inspection of filament winded beams. A complete test rig illustrated in figure 6 was constructed in order to reduce the scanning time. While the beam rotates the probe is moved from one end to the other of the beam. When the scarming is complete it is saved on diskette and can then be evaluated on a PC. The scanner is controlled by the P-scan system, which enables the results to be presented in three dimensions (Top, Side and End view). 

Hybrid Processes. There are also hybrid processes that have evolved to meet specific product needs. As an example, automotive leaf springs utilize a filament winding system to prepare impregnated fiber bundles that are then compression molded to final configuration. 

Parts with fiber volume fractions up to 60% can be fabricated by filament winding. The procedure is often used to manufacture composite rocket motors, corrosion-resistant tanks and storage containers, and piping for below-ground appHcations. 

Ease of cure, easy removal of parts from mold surfaces, and wide availabiHty have made polyesters the first choice for many fiber-reinforced composite molders. Sheet mol ding compound, filament winding, hand lay-up, spray up, and pultmsion are all weU adapted to the use of polyesters. Choosing the best polyester resin and processing technique is often a challenge. The polyester must be a type that is weU adapted to the processing method and must have the final mechanical properties requked by the part appHcation. Table 1 Hsts the deskable properties for a number of fiber-reinforced composite fabrication methods. 

Applications. Epoxy resias constitute over 90% of the matrix resia material used ia advanced composites. In addition, epoxy resias are used ia all the various fabrication processes that convert resias and reinforcements iato composite articles. Liquid resias ia combiaation, mainly, with amines and anhydride are used for filament winding, resia transfer mol ding, and pultmsion. Parts for aircraft, rocket cases, pipes, rods, tennis rackets, ski poles, golf club shafts, and fishing poles are made by one of these processes with an epoxy resia system. 

In this section a selection procedure will be developed for injection moulding, since this process is used for the widest range of materials. The choice available for other processes such as, for example, compression moulding, filament winding and vacuum forming, is much more restricted. The approach described will be less mechanistic than the systems described in the two previous sections, requiring the prospective user to be aware of the properties of the various materials available. Because the approach is somewhat different, it would be instructive to run it parallel to the above processes and compare the results. 

Filament winding Process in which continuous strands of roving or... 

The Automatic processes are those such as pultrusion, filament winding, centrifugal casting and injection moulding. 

Figure 1-11 Filament Winding a Rocket Motor Case...

Unidirectional construction Refers to fibers that are oriented in the same direction, such as unidirectional fabric, tape, or laminate, often called UD. Such parallel alignment is included in pultrusion and filament winding applications. 

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