Fatigue fibre type

The fabric substrate used for the filter media will need to provide certain characteristics, dependent on the application. The typical properties required include abrasion resistance, stretch resistance, dimensional stability, and resistance to flex fatigue. All these performance criteria can be assessed by using suitable test methods. The fabric will also be tested for correct warp and weft sett, air permeability, thickness, density, and fabric tensile properties. All the factors will affect the performance of the filter as they are directly related. If woven fabrics are considered, the porosity will be directly related to the sett and therefore air permeability. The combinations of the fibre types, fabric constructions, and coating substrate will provide the filter manufacturer with a range of properties for use in a range of appUcations. 

Another function of the fibres is to increase the relative surface area of the mixture so as to incorporate higher percentages of bitumen and thus reduce the rate of oxidation of bitumen. Reduction of the rate of oxidation increases the pavement s service life (improves fatigue life and slows appearance of ravelling). From all fibre types, cellulose fibres have been found to allow the higher increase of bitumen content in the mixture (Peltonen 1989). 

The creep and fatigue behaviour for natural fibre-reinforced plastics is less weU understood than for glass fibre-reinforced plastics because of the lack of systematic and detailed information. Limited information is currently available oti the effects on the fatigue behaviour of natural fibre-reinforced plastics of different composite parameters such as fibre type, the quality of fibre-matrix adhesion and fibre properties and their content. 

AF used in the construction industry are better known by the trade names Kevlar and Twaron. Each is a family of fibre types rather than a particular one. AF are approximately 12 pm in diameter. They have high strength and fatigue performance, intermediate modulus, good moisture and chemical resistance, and well known for their excellent impact resistance. 

These data imply that the fatigue strength is dominated by fibre type, i.e. glass rather than resin type or fibre length (provided the fibres are longer than the minimum length to transfer the load). 

The slope of the normalized stress/fatigue life curve versus fibre modulus is summarized in Figure 10.29. This shows the effect of fibre type, modulus and lay-up for carbon and glass composites. It is clear that the higher the modulus, the lower is the rate of loss of strength during fatigue. 

General FRP composites generally have very good resistance to fatigue, although the fatigue performance of FRP composite materials depends on the matrix composition and, to some extent, on the type of fibre (Curtis... 

Fatigue strengths should, wherever possible, he determined on the basis of tests on samples of the FRP laminate made with similar resin and glass fibre reinforcement of similar type and proportions. The conditions of the test should be appropriate to the loading conditions of the component being designed, and to the environmental conditions. 

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