Fibre reinforcements mechanical properties

Yoshida H, Miyata N, Naito K, Ishikawa S, Yamagishi C, Influence of orientation angle of fibre on mechanical properties in uni-directional and two-directional carbon fibre reinforced SiC composites, J Ceramic Soc Japan, 102(11), 1016-1021, 1994. 

Natural polymeric fibres, mostly cellulosics, have been used since ancient times for reinforcement. Mechanical properties of these are inferior to glass, carbon or aramid fibres. Cellulosics are usually used as a laminating material, in the woven form. Processing... 

Keywords Polyethylene composites, sustainable materials, lignocellulosic fibres, natural fibres, surface treatment, reinforcing, mechanical properties... 

The mechanical properties of plastics materials may often be considerably enhanced by embedding fibrous materials in the polymer matrix. Whilst such techniques have been applied to thermoplastics the greatest developents have taken place with the thermosetting plastics. The most common reinforcing materials are glass and cotton fibres but many other materials ranging from paper to carbon fibre are used. The fibres normally have moduli of elasticity substantially greater than shown by the resin so that under tensile stress much of the load is borne by the fibre. The modulus of the composite is intermediate to that of the fibre and that of the resin. 

The highest mechanical strengths are usually obtained when the fibre is used in fine fabric form but for many purposes the fibres may be used in mat form, particularly glass fibre. The chemical properties of the laminates are largely determined by the nature of the polymer but capillary attraction along the fibre-resin interface can occur when some of these interfaces are exposed at a laminate surface. In such circumstances the resistance of both reinforcement and matrix must be considered when assessing the suitability of a laminate for use in chemical plant. Glass fibres are most commonly used for chemical plant, in conjunction with phenolic resins, and the latter with furane, epoxide and, sometimes, polyester resins. 

The mechanical properties of pure polymeric materials are often inadequate for particular applications, and to overcome this problem these materials may be reinforced in some way. The most common method is to include a substantial amount of a rigid filler or fillers, generally as finely divided powder, or as rods or fibres. For certain materials, elastomeric particles may be used, and these have the effect of reducing brittleness. 

A pyrolysis technique was investigated as a method for the chemical recycling of glass fibre-reinforced unsaturated polyester SMC composites. The proeess yielded liquid products and gases and also a solid residue formed in the pyrolysis of glass fibres and fillers. The solid residue was used as a reinforeement/filler in unsaturated polyester BMC composites, and the influenee on mechanical properties was studied in comparison with BMC prepared entirely from virgin materials. 

Attempts have been made to improve the mechanical properties of these cements by adding reinforcing fillers (Lawrence Smith, 1973 Brown Combe, 1973 Barton et al, 1975). Lawrence Smith (1973) examined alumina, stainless steel fibre, zinc silicate and zinc phosphate. The most effective filler was found to be alumina powder. When added to zinc oxide powder in a 3 2 ratio, compressive strength was increased by 80 % and tensile strength by 100 % (cements were mixed at a powder/liquid ratio of 2 1). Because of the dilution of the zinc oxide, setting time (at 37 °C) was increased by about 100%. As far as is known, this invention has not been exploited commercially. 

Scholtens, B. J. R. and Brackman, J. C., Influence of the film former on fibre-matrix adhesion and mechanical properties of glass-fibre reinforced thermoplastics, J. Adhes., 52, 115 (1995). 

The concept of polymer reinforcement by monomolecular fibres is already old but many studies date from the last decade. The interest is particularly the very high aspect ratios and the levels of reinforcement with expected mechanical properties as high as ... 

Results are presented of experiments undertaken by Gaiker in the manufacture of sandwich panels containing foam cores based on PETP recycled by a solid state polyaddition process developed by M G Ricerche. Panels were produced with glass fibre-reinforced unsaturated polyester and epoxy resin skins, and allthermoplastic panels with PE, PP, PS and glass fibre-reinforced PETP skins were also produced. EVA hot melt adhesives and thermoset adhesives were evaluated in bonding glass fibre-reinforced PETP skins to the foam cores. Data are presented for the mechanical properties of the structures studied. 

Table 3.10 Mechanical properties of freeze-gelled, unidirectional carbon-fibre-reinforced CMC made by hand lay-up73...

Table 3.11 Mechanical properties of some fibre-reinforced sol-gel glass-matrix composites73...

The impact of thermal shock on the properties of a ceramic or a CMC is assessed by means of both destructive and non-destructive testing methods. Flexural or tensile (mainly for CMCs) tests of suitably-sized thermally shocked specimens are usually employed to measure retained mechanical properties as a function of the temperature difference. The temperature differential for which a significant drop in property values is observed is the A A- For monolithic ceramics and particle- or whisker-reinforced CMCs the property under investigation is usually strength, whereas in fibre-reinforced CMCs a drop in Young s modulus is usually a better indication of the onset of damage. 

In the following paragraphs an overview of damage due to thermal shock and its effect on the mechanical properties of CMCs with different fibre architectures is provided for a number of different reinforcement architectures. Subsequently, the effect of thermal shock on interfacial properties is discussed, followed by a description of attempts to analyse and model the thermal shock behaviour of these materials. 

This chapter has reviewed the performance of CMCs under conditions of thermal shock. It has been shown that CMCs exhibit superior resistance to thermal shock, compared with their monolithic counterparts, as catastrophic failure can always be avoided. Resistance to higher temperature differentials and property retention after the onset of thermal shock cracking (especially in fibre-reinforced CMCs) can be realised, provided that the mechanical and thermal properties of CMCs are optimised by careful choice of their constituents. 

Bhatt, R.T., Phillips, R.E. (1990), Thermal effects on the mechanical properties of SiC fibre reinforced reaction-bonded silicon nitride matrix composites , J. Mater. Sci., 25, 3401-3407. 

Blissett, M.J., Smith, P. A., Yeomans, J.A. (1997), Thermal shock behaviour of unidirectional silicon carbide fibre reinforced calcium aluminosilicate , J. Mater. Sci., 32, 317-325. Blissett, M.J., Smith, P.A., Yeomans, J.A. (1998), Flexural mechanical properties of thermally treated unidirectional and cross-ply Nicalon-reinforced calcium aluminosilicate composites , J. Mater. Sci., 33, 4181 —4190. 

Polyether ether ketone (PEEK) and Polyether sulphone (PES) belong to the most recent developments in the field of technical high-performance polymers. Both possess very good thermal and mechanical properties, which can be further improved by reinforcing fibres. Their application is mainly in aircraft and space vehicles. 

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