Unidirectional prepreg material

Figure 21.34 Polished cross-sections of equivalent UD tape and Liba NCF lamintes. (a) Unidirectional prepreg composite laminate, (b) Liba NCF composite laminate. Source Reprinted with permission from Mills A, Burley G, Backhouse R, 44th International SAMPE Symposium, May 23-27, 1999. Copyright 1999, The Society for the Advancement of Material and Process Engineering (SAMPE).

Figure 1.210 shows the individual steps in manufacturing the component. The basic material for making monolithic fiber products are pre-impregnated liber fabrics or unidirectional libers. Prepreg material on an epoxy resin base has a limited handling time and can be stored for a longer period of time only at temperatures of about-18 °C. 

Gordon Aerolite was the result of work on phenolic moulding materials for the manufacture of variable pitch propellers for de Havilland. The use of continuous flax fibres enabled de Bruyne to produce unidirectional prepregs instead of producing reinforced mouldings. 

One common laminate material is unidirectional prepreg tape, which can conveniently be laid-up in predetermined high-strength orientations. 

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. 

The huge, hollow mast was fabricated in five internally heated female molds. Stitched unidirectional carbon/epoxy prepreg from Cytec Engineered Materials Inc. of Wrexham Clwyd, U.K. was hand laid up to form the two back sections and the three front sections. Cure was controlled by a computer that monitored the mold heating system to prevent excessive exotherm heat. The five cured sections were bonded... 

Most carbon fibre reinforced plastics (CFRP) used and investigated to date are produced from preimpregnated continuous carbon fibre prepregs. Polymers reinforced with aligned short carbon fibres have certain advantages as materials for structural components, because they can easily be formed into complicated shapes with satisfactory mechanical properties. Woven fabrics produced from carbon fibres find increasing application in the aerospace and many other industries, because they are easy to handle, they have the ability to conform to complicated shapes and the in-plane properties are more isotropic than those of equivalent unidirectional materials. 

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