Fibre reinforced polymer composites thermosetting matrices properties

Fibre-reinforced polymer (FRP) composites are composed of fibres and matrices, which are bonded through the interface to ensure that the composite system as a whole gives satisfactory performance. Part 1 deals with FRP composite matrix materials which provide the foundation for composite materials. Chapter 2 reviews the chemistry of phenolic resins together with their mechanical and thermal properties. Chapter 3 discusses polyester thermoset resins as matrix materials. An overview of the chemistry of vinylester resins, together with their mechanical and chemical properties, as well as their use as a matrix material in the construction industry, is provided in Chapter 4. The final chapter in Part 1 begins with a review of the epoxy resins commonly available on the market, and then focuses on the principal characteristics of epoxy resin composite systems and their practical applications. 

Polymer composites are plastics within which fibres are embedded. The plastic is known as the matrix (resin) and the fibres dispersed witbin it are known as the reinforcement Thermosetting matrix materials include polyester, vinyl ester and epoxy resins. For higher temperature and extreme environments, bismaleimlde, polyimide and phenolic resins are used. Composites can be used to replace metal parts but care must be taken during design. Most engineering materials have similar properties in any direction (called isotropic) where composites have not This can however be offset by arranging the reinforcement layers in varying directions. 

So far when considering carbon fibre composites the matrix has been a thermosetting resin or polymer. The relative merits of thermosetting and thermoplastic polymer matrices were discussed briefly in Chapter 3. Several thermoplastic matrices are compounded with short carbon or glass fibres. In Table 5.22 however the properties of unidirectional, continuous, carbon fibre-reinforced materials are illustrated. 

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. 

Composites are made up of individual materials these are referred to as constituent materials. The purpose of a composite is to create a material that combines its constituent parts in some beneficial way. The two main categories of constituent materials are the matrix and the reinforcement. The synthetic matrix materials are either thermoplastic or thermosetting resins. These polymers bind the reinforcement together and determine the physical in-service properties of the composite material. Polymers can also act as reinforcing material in composites Kevlar for instance, is a synthetic polymer fibre that is very strong and imparts toughness to a composite. 

It is interesting to compare the efficiency of the reinforcement for AS4 fibre in PPS and PEEK. In the former case the values are 92% and 63% for modulus and strength respectively and in the latter 99% and 87% respectively. Modulus uptake is excellent in both cases and strength in the second. The poorer strength result for PPS may be due to reduced compatibility between the fibre surface and matrix. This is supported by the lower ILSS value for PPS carbon fibre composite. Compressive properties are notably lower than tensile ones, while transverse tensile properties are similar to those of thermosetting polymer matrix materials. 

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