Fibre unidirectional sheet

Consider a unidirectional sheet of material with the fibres aligned in the x-direction and subjected to a stress, If the sheet has thickness, h, as shown in Fig. 3.15 and we consider unit width, then the normal axial force Nx is given by... 

GMTs are thermoplastic resin sheets or blanks reinforced with glass mat. Possibly, unidirectional continuous fibres can also be used. 

Fibrelam board skins coasist of unidirectional glass-fibre/epoxide resin. The skins are pre-made in the form of sheets for subsequent bonding to the honeycomb core. 

Intermediate mixed product of an uncured composite (with continuous unidirectional or woven fibres) with catalysed resin matrix material, ready for cure, usually in flexible sheet form. 

It was reported by Sun and Chen (2010) that unidirectional Dyneema fabric showed reduced ballistic performance in terms of energy absorption when compared on a single-layer basis a panel composed of unidirectional Dyneema fabric sheets demonstrated better trauma proof ability. Compared to the 2D fabrics, 3D fabrics offer more possibilities for fibre orientation and fibre networking. For this reason, 3D fabrics have been paid attention for various applications such as in critical stmcture, automobile, aircraft and protective clothing in recent years. 

Flat laminates can be produced using the processes described in other chapters of this handbook. For example, a double belt press or compression moulding can produce the precursor laminate. Figure 5.3a shows thermoplastic composites with unidirectional fibres in each layer consolidated into a laminate with a picture frame mould. A picture frame mould goes into a hot press or autoclave and turns composite lamina into a fused precursor. To some extent, sheet forming adds cost to a final structure because a manufacturer creates two components the flat precursor and the formed structure. 

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)... 

The laminates consist of alternate layers aluminium (0.2-0.5 mm thick], which has been anodised and then primed with Cytec-Fiberite s BR-127 corrosion-inhibiting primer, bonded together with fibre-rich, epoxy-based adhesive-prepregs (about 0.125 mm thick]. The reinforcing fibre is usually unidirectional in nature, although woven fabric is occasionally used. Generally two or three sheets of adhesive separate each sheet of aluminium this can be in the 0° direction or laid up in a cross-plied orientation. 

Several methods have been developed for the manufacture of films and sheets from thermotropic LCP materials. Bayer has presented a technique to form oriented sheets and films from fibres by pressing at a temperature at which the fibres melt to form a matrix without losing their molecular orientation. For unidirectional mouldings moduli of the order of 50-60 GPa at a tensile strength of 400-500 MPa were obtained... 

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