Prepregs unidirectional

An alternative approach to building up components in which the fibres are aligned in various directions, which is often favoured with carbon fibres, is to produce a pre-impregnated material, known as a prepreg. Unidirectional fibres are spread out thinly and impregnated with a thermosetting resin which is partially cured or B-staged. The sheet or roll material (which is a fraction of a millimetre in thickness)... 

Fulcrum (Fulcrum Composites) is a unidirectional prepreg with fibre levels up to 70% in volume. 

Table 6.36 displays basic property examples of glass mat thermoplastics (GMT) thermoplastic prepregs and glass or carbon reinforced unidirectional composites. 

Effect of through-the-thickness stitches on flexural strength and Mode I interlaminar fracture toughness of carbon fiber-epoxy matrix composites manufactured using unidirectional prepregs". 

Thus, the fiber is impregnated in the partially cured resin. Depending upon the assembly the fiber is usually unidirectional, but they can also be made bidirectional or some other combination. The process of fitting the prepreg into, generally onto, the mold is called layup. Generally a number of layers of prepreg are used. The lay-up may be done by hand, called hand lay-up, or done automatically, or by a combination of automatic and hand layup. As expected, hand lay-up is more costly but is essential where one-of-a-kind products are produced. 

Techniques commonly used to manufacture advanced composites from prepregs, which are available in unidirectional fiber or fabric form, include compression molding, vacuum-bag autoclave molding, stamp molding, thermoforming, and on-line (in situ) consolidation [3]. In compression and vacuum-bag autoclave molding techniques, the prepreg is cut to the dimensions of the structure, and the fiber directions are oriented to obtain the required... 

Figure 7.6 A schematic representation showing two unidirectional prepreg plies in contact at the beginning of consolidation...

Figure 7.18 Consolidation time (tc) versus consolidation pressure for T300/P1700 and APC-2 Batch II prepregs. (a) Unidirectional lay-up. (b) Cross-ply lay-up...

The constant k is called the Kozeny constant and it attains a value of 0.7 for well-ordered reinforcements with uniformly distributed fibers, (e.g. unidirectional prepreg) [17]. For commonly used fabrics in LCM (e.g., continuous strand mat or weaves) R2/4k should be seen as an adjustable model parameter with only weak coupling to the fiber or fiber bundle diameter. 

Unidirectional carbon fiber prepreg manufactured by Sunkyung Industry Co., Suwon, Korea. 

Unidirectional prepreg, aligned, unidirectional fabrics, pultruded (aligned) rods, filament hoop wound cylinders... 

Fibers and base resins are supplied against certificates of conformance and often property test certificates. On-line control during the manufacture of prepreg revolves around the correct ratio of fiber to resin. This is done by a traversing Beta-gauge, which scans the dry fiber (either unidirectional of fabric) and then the impregnated fiber and provides a continuous real-time plot of the ratio across the width of the material. This can be linked back to the resin system application point for continuous adjustment. 

Finally, the prepreg were stacked unidirectionally (0°) and moulded into coupons of 3 mm thick by 6 mm long by compression moulding at 200°C for 15 mins and then quenching under pressure. 

Manufacturers of composite structures have traditionally used prepreg tape to manufacture structural components. Fibres are initially combined into unidirectional tows (bundles) of fibres combined into fabrics, e.g. by weaving or knitting. The vast majority of the tows employed in woven, braided or knitted reinforcements comprise low twist or untwisted continuous filament yams. Three-dimensional technical textiles can be produced by weaving [5], knitting [6] and braiding [7] or as non-crimp fabrics. 

In the AFP process, multi-headed robot machinery lays down multiple strands of prepregged fibre on either flat tools, curved mandrels or complete cylindrical mandrels or drums (as applied in manufacture of fuselage sections of the Boeing 787). The process is shown in Figure 3.4. The ATL variant of the process lays down tapes of unidirectional prepreg up to 300 mm wide across the mandrel. The AFP process uses smaller width ribbons of prepreg a few millimetres wide and can... 

The ATL and AFP processes are thus a cross between filament winding with its elaborate automated patterns of fibre laydown and unidirectional prepreg layup with its reliance on the autoclave. The use of automated robotic machinery for the layup gives increased layup speed (vital to economically manufacture these large items in feasible timescale), consistency and freedom from errors compared with manual techniques, as well as ensuring precision in the placement of the tows and tapes. 

Figure 5.5 Level of fibre misalignment in a typical as-delivered unidirectional prepreg.

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