Unidirectional rovings

The temperature dependence of the absorbed energy for standard specimens is shown in Figure 1. Impact behaviors and fracture modes of edge notched specimens depending on temperature were reported elsewhere (9, 10). In edge notched specimens of unidirectional roving reinforced material (GC 68 wt % ), cloth laminates, and mat reinforced material the fracture mode changed with temperature all materials re-... 

Local indentation at the point of impact may contribute to picking in absorbed energy with increasing temperatures. There was clear indentation for unidirectional roving reinforced specimens that seemed to increase with increasing temperatures. For cloth specimens a slight indentation was observed above 100 °C. 

Mats are the cheapest form of planar reinforcements but are more expensive than unidirectional rovings. They are made by chopping rovings into short lengths and assembling them into a handleable mat with a binder which may be insoluble or soluble in water. The latter should be avoided for applications where water immersion is foreseen as this can be the cause of osmosis effects and lead to loss of composite integrity. Thermoplastic binders are also used to allow mats to be formed into shaped preforms for... 

Manufacture was achieved through either contact moulding by hand lay-up, or filament winding of unidirectional rovings. 

The effect of varying the reinforcement from unidirectional rovings through to balanced combination fabrics is shown in Figure 11.5 and Table 11.19. 

Structures Unidirectional (roving, yam) Nonwoven (felts, papers, filament wounded or placement) weave (plane, triaxial) hi- and triaxial braides knitted Z-pinned, needled punched, stitched Tridimensional braids, 3D weave (orthogonal, angle interlock, multilayer), nD multi axial weave... 

Unidirectional rovings can be used directly in composite manufacture, or they can be converted to otho- intmnediate products. Direct applications include the unidirectional rovings used in processes such as spray lay up, filament winding, and pultrusion. Pul-tmsion is the process in which glass rovings or tows, in a preselected orientation, are saturated with resin and pulled through a heated die, where the part is formed and cured. 

The price of the fibrous reinforcements (Figure 2.14) depends on the nature of the fibres and the form of the reinforcement continuous or chopped fibres, mats, rovings, fabrics or unidirectional. 

Another form is the glass cloth, composed of rovings. Weaving can take place in various patterns, varying from practically unidirectional to square weaves with equal properties in the two main directions. 

No. 4 structure in Figure 52 shows another composite structure consisting of unidirectional reinforcement with continuous roving. This structiure was employed by Polymetrics Corp., and NPC, Inc. (25). 

Bulk Molding Compound Sheet Molding Compound Chopped Strand Mat Woven Roving Unidirectional Axial Unidirectional Transverse... 

The systems can include many options surfiice veil, chopped liners, sprayed resin systems, hoop winding strands, helical winding strands, resin bath, unidirectional tape, woven roving tape, pigmented resin surfaces, wax-resin surfaces, gel coats, BPO catalyst, epoxy resins, vinyl ester resins, filled resin systems, abrasive resin systems, polyester foam, syntactic foam, and charting film. 

Continuous bundles of glass filaments are termed roving. They can be used directly in some of the most widely used fabrication procedures, such as filament winding, as well as in pultrusion (see later in the chapter for details of these techniques). The roving is unidirectional. 

Woven fabrics are constructed by interlacing warp and weft yarns, fibres or filaments in a variety of patterns to form fabric styles such as plain, twill, satin, unidirectional and others. Woven fabrics are usually lighter than woven rovings, have less crimp and may achieve volume fractions of over 50% depending on the method of composite compaction. 

Unidirectional rovin i cloth (orientated) is a variation of woven roving where the fibers are arranged to provide greater strength in a specific direction or directions (such as by using heavier roving for the warp and lighter for the weft/Chapter 7). 

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