Prepreg draping

Prepreg draping and consolidation by vacuum or pressure bag moulding, autoclave... 

Bismaleimide Resins via EI E Reaction. The copolymerization of a BMI with o,o -diallylbisphenol A [1745-89-7] (DABA) is a resia coacept that has beea widely accepted by the iadustry because BMI—DABA bleads are tacky soHds at room temperature and therefore provide all the desired properties ia prepregs, such as drape and tack, similar to epoxies. Crystalline BMI can easily be blended with DABA, which is a high viscosity fluid at room temperature. Upon heating BMI—DABA blends copolymerize via complex ENE and Diels-Alder reactions as outlined ia Eigure 8. 

The resin system V-378A, mentioned eadier, is a bismaleimide system that has been modified with divinylbenzene to achieve drape and tack in prepreg form. Divinylbenzene-modifted BMI is appreciated because of its outstanding hot—wet environmental resistance and epoxylike cure (18). 

Imides - Polyimides (PI) have been conventionally prepared by the chemical or thermal cyclodehydration of polyamic acids formed from the solution reaction of aromatic tetracarboxylic dianhydrides and aromatic diamines. The early PI were insoluble and relatively intractable. The polyamic acid was the processable intermediate. However, the polyamic acid precursor has two major shortcomings, hydrolytic instability and the evolution of volatiles during the thermal conversion to PI. In addition, residual solvent was left in adhesive tapes and prepregs to obtain tack, drape and flow. During the fabrication of components, the evolution of volatiles caused processing problems and led to porosity in the part. As work progressed on PI, other synthetic routes were investigated (e.g. reaction of esters of aromatic tetracarboxylic acids with diamines... 

Techniques for locating and orienting them onto a molding surface, in accordance with the design pattern, are adapted to the tack and drape characteristics of the prepreg. The woven fabrics make possible... 

Thermoset prepregs can be formulated and processed to have various degrees of drape. Thermoplastic prepregs are very woody and have little drape therefore, they generally need to be heated to form around sharp mold sections. 

Combinations of reinforcing fibers and thermoplastic fibers are made where the thermoplastic becomes the binder in finished parts. In some cases slit polymer films are used instead of polymer yams. These prepregs generally have good drape and handling. 

A rather common application of fibre reinforced polymers is car repair. This poor mans technology is translated to the "high tech" area. The most important difference is found in the addition of the word "advanced". For also in the aircraft industry composites is a sticky business. Prepregs are draped in moulds by hand, moreover, they are cured in expensive autoclaves. 

In attempts to improve processibility and introduce tack and drape into PI prepregs and adhesives without using solvent, a PMR-type resin, LARC-160, was developed at NASA-Langley. This resin uses a commercially available liquid aromatic diamine, Jeffamine AP-22 or Anacamine DL (19),... 

Kaufmaim M, Zenkert D, Akermo M (2010), Cost/weight optimization of composite prepreg structures for best draping strategy . Composites A, 41, 464-A72... 

Prepreg tack/drape Good None Simplified by co-min-gled fibers... 

Fabrics provide a wide range of properties and are chosen for both ease of drape (fine being better than coarse) and fibre orientation. Prepreg systems are available with fabrics as well as fully aligned rovings. 

Prepreg materials are thin, typically 0.2 mm thick, so that many layers are required to obtain a reasonable thickness, which does permit layers to be orientated so as to obtain specified properties. Drape can be a problem because of the continuous nature of the fibre so care is required in laying up. 

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