Glass fibre compositions

Epoxide resins reinforced with carbon and Aramid fibres have been used in small boats, where it is claimed that products of equal stiffness and more useable space may be produced with a 40% saving in weight over traditional polyester/ glass fibre composites. Aramid fibre-reinforced epoxide resins have been developed in the United States to replace steel helmets for military purposes. Printed circuit board bases also provide a substantial outlet for epoxide resins. One recent survey indicates that over one-quarter of epoxide resin production in Western Europe is used for this application. The laminates also find some use in chermical engineering plant and in tooling. 

The poor stability on exposure to air and water, particularly at elevated temperatures, which results in a reduction in conductivity, also poses problems. In the case of polypyrrole it has been found that conductivity can, however, be maintained either by the drastic measure of storing under the protective layer of the inert gas argon or embedding polypyrrole film in a matrix of an epoxide resin-glass-fibre composite. 

While (1—3) are clearly variables of the matrix, the presence of residuals (4) is not so obvious since this refers to unreacted hardeners and other impurities. Impurities such as calcium, sodium or potassium salts arise from inclusions in fillers or as contaminants on the surface of reinforcing fibres. The sodium and potassium content of glass fibres has been steadily reduced over recent years because they were widely acknowledged as responsible for the water sensitivity of glass fibre composites in aqueous environments. 

In recent times, commodity thermoplastics have become signiflcant contenders as matrices for glass fibre composites where environmental resistance is sought for example, polypropylene is now available in a pre-preg form for fusion bonding. Since it has low polarity and is also partially crystalline, moisture absorption is very low. 

ECR and boron-free glass fibres have improved durability over E glass so that ESCC of glass fibre composites is less likely when modem glasses are employed. The design of glass fibre composites for resistance to stress corrosion cracking has been discussed in detail elsewhere [7,8]. 

Environmental stress corrosion cracking of glass fibre composites [33 2]... 

As a consequence, a limiting strain for stress corrosion failure may exist for a particular glass fibre composite, which is governed by the fracture toughness of the resin but the effects of fibre/matrix interfacial strength... 

Maider, E. Jacobasch, H.-J. Grundke, K. Gietzelt, T. (1996). Influence of an Optimized Interphase on the Properties of Polypropylene/Glass Fibre Composites. Composites Part A Applied Science and Manufacturing, Vol.27A No.9, pp. 907-912 ISSN 1359-835X... 

Creep rupture data for glass fibre composites in acid are less reliable than creen data as the si7e and shane of the snecimen nhviniislv influence time... 

A uni-directional glass fibre composite, with 65% fibres, will have a tensile strength of about 700 N/mm and a tensile modulus of about 40 kN/mml... 

Glass fibre composites have very good resistance to impact due to their high strain to failure, when compared with other fibres. 

Aramid FRPs have excellent impact resistance, particularly to ballistic impact. On a weight basis they are superior to glass fibre composites, which themselves offer good ballistic impact resistance, but they are more expensive. 

Figure 1.2 The effects of temperature on the dynamic mechanical behaviour of one polyester/glass fibre composite (isophthalic polyester Neste S 560 Z, E-glass, manufactured by pultrusion). The DSC method gives the Tg of the pure S 560 Z resin casting as 135°C. Owing to certain additives, the Tg of the FRP material in question could not be determined with DSC.

Glass fibre composites are susceptible to a phenomenon known as stress corrosion where a laminate under stress in an acidic or basic environment can fail catastrophically at very low stress if the environment can gain access to the fibres by diffusion or, more likely, a crack (reference 1.11). 

As glass fibre composites have a relatively low Young s modulus, axial strain can be significant. Hence it may be neccesary to apply a serviceability limit state to this criterion to ensure that if for instance the tension member is used as a brace, it adequately prevents excessive sway in the structure. In any event there is a hmiting allowable strain to ensure that the resin does not craze. 

J.K. Kim, M.L Sham, and J. Wu, Nanoscale characterisation of interphase in silane treated glass fibre composites. Compos. A Appl. Sci. Manuf. 32,607-618 (2001). 

Hameed, N., Sreekumar, P.A., Francis, B., Yang, W., Thomas, S. Morphology, dynamic mechanical and thermal studies on poly(styrene-co-actylonitrile) modified epoxy resin/glass fibre composites. Compos. A Appl. ScL Manuf. 38, 2422-2432 (2007)... 

A Misra, BL Deopura, SF Xavier, FD Hartley, RH Fetters. Transcrystallinity in injection molded polypropylene glass fibre composites. Die Angewand Makromol Chem 113 113-120, 1983. 

T-El Cheng, FR Jones, D Wang. Effect of fibre conditioning on the interfadal shear strength of glass-fibre composites. Compos Sci Tech 48 89-96, 1993. 

E Mader, H-J Jacobasch, K Grundke, T Gietzelt. Influence of an optimized interphase on the properties of polypropylene/glass fibre composites. Composites, Part A, 27 907-912, 1996. 

E Devaux, B Chabert. Nature and origin of the transcrystalline interphase of polypropylene/glass fibre composites after a shear stress. Polymer Communications 32 464-468, 1991. 

E Devaux, JF Gerard, P Bourgin, B Chabert. Two-dimensional simulation of crystalline growth fronts in a polypropylene/glass-fibre composite depending on processing conditions. Composites Sci Tech 48 199-203, 1993. 

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