Glass fibre corrosion

Plastics also find increasing use in vehicles for both water and air transport. Glass-fibre-reinforced plastic boats are widely used as a result of their economy in manufacture, ease of maintenance, lightness of weight and, for military purposes, antimagnetic characteristics. The non-corrosive nature of plastics also leads to their widespread use in boat fixtures and fittings. In aircraft, plastics are particularly useful on account of their low density. 

Technical advantage/function Basalt rock wool is used for noise insulation in automotive exhaust units for the purposes of noise absorption. Vital technical requirements are temperature resistance, noise absorption behaviour, corrosion resistance and mechanical stability. Now textile continuous glass fibres and biosoluble mineral wools are also used for this application in exhaust units. 

Glass fibres exhibit time-dependent fracture under a static load, which is referred to as static fatigue [36]. Since there is no time dependence of strength in a vacuum, it is considered that water is involved in the reduction in strength. Thus, a stress corrosion mechanism in condensed water is inferred. The chemical reactions associated with this process are given in Figure 12.17. 

Recently, Owens Coming has replaced its E-glass fibres with boron-free formulations (Advantex). These fibres have similar mechanical properties to E glass but are believed to exhibit similar durability to ECR glass fibres which were developed for corrosion-resistant applications. 

Environmental stress corrosion cracking (ESCC) of glass fibres... 

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]... 

This is the type of failure generally observed in service, since it occurs in the submerged composite at applied strains in excess of 0.15%. It is initiated by the stress corrosion failure of a glass fibre near the surface of the laminate, as a consequence of environmental diffusion. Attempts to confirm diffusion of the acidic environment through the resin to the fibre have proved difficult but it is likely that the applied stress increases the rate of diffusion. The statistical nature of fibre strength means that a premature fibre break can lead to an enhancement of the local stress in the adjacent fibres by stress transfer. Thus a series of stress corrosion nuclei will form in the surface of a 0° composite under tension. Brittle failure will occur once the flaw reaches... 

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... 

ECR glass flake can be used to provide reinforcement to the barrier layers. Resistance to highly corrosive environments can be further improved by employing ECR, Chemglass, S or R, glass fibres instead of E-glass for the structural wall. 

The stress corrosion, that is the corrosion as a result of the combined action of chemical and mechanical action, of glass fibre reinforced plastics in aqueous media has been reviewed by Roberts [73], Hogg and Hull [74] and Menges and Lutterbeck [75], although none of the work referenced is specific to sea water exposure. The subject of the corrosion of FRP under static loading is discussed in some detail in Chapter 3, and cyclic loading or fatigue is the subject of Chapters 5 and 11 in this book, but both these topics will be briefly mentioned here in the context of marine applications. 

The most widely used epoxy resins are reaction products of either bisphenol A or a novolac phenolic resin with epichlorhydrin. When used to manufacture corrosion-resistant structures for use in the chemical process industry, epoxy resins are generally hardened with either aromatic or cycloaliphatic amines. The hardeners for epoxy resins are, with few exceptions, added at levels varying from 20phr (parts per hundred resin) to lOOphr. This means that the hardener is actually quite a high proportion of the matrix resin and has quite a profound effect on the mechanical and corrosion properties of the cured resin. Thus the selection of the most suitable hardener is critical to the eventual success of the application. Epoxy resins have viscosities of several thousand mPas at room temperature, which makes it much more difficult to wet out glass fibre efficiently with them than with polyesters. Wet-out therefore involves heating the resin formulation to between 40°C and 60°C to reduce the viscosity to less than 1000 mPas. 

The tensile strength of glass fibres reduces at elevated temperatures but can be considered constant for the range of temperatures at which polymer matrices are exposed. The tensile strength also reduces with chemical corrosion and with time under sustained loading. 

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