Mechanical properties of FRP

The literature published on fracture mechanics testing of FRPs in the last 40 years comprises a large database on delamination resistance or fracture toughness of different types of FRPs. An early review [51] compiled the data available at that time. Selected data from quasi-static mode I and mode II tests on FRPs were compared by O Brien [52], and quasi-static mode I test data from carbon—fibre epoxy and poly-ether-ether-ketone (PEEK) by Brunner [53]. Mechanical properties of FRP composites are compiled in the Composite Materials Handbook version F (2002) [9—11], but this does not comprise fracture mechanics data. Hence, there is no comprehensive and up-to-date database on the available data or literature. 

The mechanical properties of FRPs are influenced by the characteristic nature of its components, as shown in Fig. 1. 

This concept is applied in Chapters 4 and 5 that describe the temperature-dependent thermophysical and mechanical properties of FRP composite materials subjected to elevated temperature and fire. In Chapter 3, however, the estimation of the effective properties of a material mixture through a distribution function of its individual components (in different material states) is introduced first. 

FRP composites under elevated temperature and fire mostly correspond to a mixture of two material states, because - although three material states can be found in the full temperature range - only two states exist at a certain time. The thermophysical and mechanical properties of FRP composites under elevated temperature and fire estimated by the rule and inverse rule of mixture will be presented in Chapters 4 and 5 respectively. 

In this chapter, existing models for describing the change of mechanical properties of FRP composites under elevated temperatures and fire have been reviewed. On the basis of a kinetic description of the involved physical and chemical processes, the modeling approach developed in Chapters 2-4 has been further extended to predict the degradation of mechanical properties. Those mechanical properties... 

It follows that other mechanical properties of FRP laminates will degrade at these higher temperatures. However, the retention of the mechanical properties is substantially increased as the glass content is increased. 

Table 6.6 Mechanical properties of FRP composites based on difunctional and multifunctional epoxies [40, 65, 71] ...

The mechanical properties of FRP composites depend on the type of fibre nsed in their production and the fibre content in the final product. These aspects are likely to vary between competing composite products since there is currently no agreed standard specification for their production. Therefore, all design must be based on the actnal properties supplied by the manufacturer and laboratory test results. 

The most relevant mechanical properties of FRP for structural applications are the tensile strength, modulus of elasticity and the ultimate elongation at failure. Some representative values compiled from the literature are given in Table 5.2 for high performance long fibres suitable for structural applications. 

When exposed to fire, the mechanical properties of FRP systems laid up on external surfaces can be considerably improved by increasing the thickness of the coating used. It is strongly advised to use coatings that limit flame propagation and exhaust fumes. In any case, certified insnlation systems are recommended. 

The mechanical properties of FRP composites are dependent upon the ratio of fibre and matrix material, the mechanical properties of the constituent materials, the fibre orientation in the matrix, and ultimately the processing and methods of fabrication, which are the subject of Part II. Chapters discuss prepreg processing, liquid composite moulding (LCM), filament winding processes and pultrusion of advanced fibre-reinforced polymer (FRP) composites. 

Table 9.4 presents typical ranges of variation for several physical and mechanical properties of FRP bars made of glass (GFRP), carbon (CFRP) and aramid (AFRP) reinforcement. For the typical fibre content, all FRP reinforcing bars present low density, about one-sixth to one-quarter that of steel bars (again, the main competitor), which facilitates transport and... 

Table 9.4 Typical physical and mechanical properties of FRP reinforcing bars...

An further alternative approach being developed worldwide is to replace the steel completely by fibre-reinforced plastics (FRP), which consist of continuous fibres as carbon, glass or aramid, set in a suitable resin to form a composite rod or grid. These materials have high tensile strength, low density and are non-magnetic they can be used both for new structures and for repair of existing ones. The mechanical properties of FRP are determined by the amount and type of fibre, while the durability will be a function of both the resin and the fibre. 

Silane coupling agents adsorb onto the surface of glass fibers as multilayers. The amount of adsorbed silane is a function of the concentration of silane treating solutions. Since the mechanical properties of FRP have some correlations with the amount of coupling agent present, it is important to determine the concentration dependence of the silane adsorption. Johannson eJt reported the first correlation using C-labeled Y MPS. 

The rate, at which mechanical properties of FRP products are reduced, decreases with the time approximating to a half - logarithmic function. Once the first retention dates have been plotted, a straight line may be drawn to predict the retention of lifetime of FRP products in different sulfur acid environments. 

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