Fibre-reinforced Laminates

There are, essentially, two types of fibre-reinforced laminates and both — those with thermoplastic and those with thermosetting matrices — can be pretreated 

Utilising somewhat similar methodologies each type of matrix, though, has its own special considerations. 

The optimum pretreatment for the preparation of composite substrates for adhesive bonding can be defined as one which removes all the surface matrix system, to expose the reinforcing fibres, without doing any damage to the fibres themselves. 

Obviously, at present, it is not feasible to achieve such a surface. However, the best possible procedures which can be employed are given below. 

Currently the most commonly encountered substrates are those produced using polyetheretherketone (PEEK) or polyethersulphone matrices, especially reinforced with carbon fibre. 

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The markets for polyetherimides arise to an extent from stricter regulations concerning flammability and smoke evolution coupled with such features as high strength, toughness and heat resistance. Application areas include car under-the-bonnet uses, microwave equipment, printed circuit boards and aerospace (including carbon-fibre-reinforced laminated materials). The polymer is also of interest in flim, fibre and wire insulation form. 

Of the phosphorus-containing polymers the polyphosphates have been known for many years. Aluminium phosphate had been used in the manufacture of heat-resistant silica-fibre-reinforced laminates. 

Thermal decomposition of the matrix material offers a simple way of recovering the relatively expensive reinforcing fibres from a fibre-reinforced laminate. The epoxy resin matrix was made to decompose by thermal treatment in air or nitrogen, this treatment allowing the carbon fibres to be recovered without damage. 

Laufenberg TL, Rowlands RE and Krueger GP (1984) Economic feasibility of synthetic fibre reinforced laminated veneer lumber. Forest Products Journal, 34(4) 15-22 Lavers GM (1969). The strength properties of timbers. Princes Risborough Laboratory Bulletin 50, HMSO, London... 

Cartie DDR, Troulis M, Partridge IK. Delamination of Z-piimed carbon fibre reinforced laminates. Compos Sci Technol 2006b 66 855—61. http //dx.doi.org/10.1016/ j.compscitech.2004.12.018. 

The elastic mechanical properties of carbon fibre-reinforced laminates are highly dependent on the properties of the fibres and the matrix chosen and on the direction of loading relative to the fibre orientation. In a unidirectional laminate, with all fibres orientated in one direction and loaded parallel to the fibres, the properties are mainly dependent on those of the fibres and can be estimated by the rule of mixtures, taking into account the volume fractions of the fibres and the matrix. Equation [5.1] shows that E, the Young s modulus parallel to the fibres is simply given by... 

High performance polyethylene fibres such as Dyneema (a reinforcing polyethylene fibre from DSM) show a pronounced time-dependent behaviour under static loading conditions. An increase in strain rate and/or decrease in temperature results in an increase in fibre modulus and strength, but a decrease in work of fracture [33]. It is also known that creep can be observed even in unidirectional PE-fibre reinforced laminates. How far this specific behaviour influences the fatigue behaviour is of great interest and has to be investigated in order to find the appropriate applications for PE-composites. 

K Schulte, K Friedrich and G Hostenkamp, Temperature dependent mechanical behaviour of PEI and PES resins used as matrices for short fibre reinforced laminates , J Mater Sci 1986 21 3561-3570. 

Subsequent experience has shown that fibre reinforced laminates have the potential to provide extended service in the marine environment. Early losses in mechanical strength have tended to stabilize after a year or so. However, it is essential that all the constituents of the material are selected carefully to avoid the inclusion of hygroscopic/hydrophilic components. Careful control of the manufacturing process is likely to improve the durability of the product considerably. 

Hodgkiess et al [78] exposed glass fibre reinforced laminates to (i) distilled water, (ii) simulated sea water ( Ocean Salt 3.3% total dissolved solids) (iii) simulated spray/sunlight conditions in the laboratory and (iv) to tidal effects and permanent immersion in the lower Clyde estuary (55°45 N 4°55 W), where the sea water temperature was 6-12°C over the period of testing. The materials tested, which were exposed for up to 18 months with all sides and edges coated in the same resin, were ... 

Harding J, Dong L, Effect of strain rate on the interlaminar shear-strength of carbon-fibre-reinforced laminates. Composite Science and Technology, 51(3), 347 358, 1994. 

Zhu XY, Li ZX, Jin YX, Laminar fracture-behavior of (carbon glass) hybrid fibre reinforced laminates, . Laminar fracture process, J Eng Eracture Mechanics, 44(4), 545, 1993. 

Quaresiinin M and Vai-ley R J (2008) Understanding the effect of nano-modifier addition upon the properties of fibre reinforced laminates. Compos Sci Technol 68 718-726. 

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