Foams and reinforced plastics

Occasionally, the attractive properties of polymers fall short of the needs of a designer. One way of altering these is to include an additive to improve properties to those required. Blowing agents and reinforcing fillers will change the basic properties of a polymer as well as the mechanical properties, the melt 

Short-fibre composites are most commonly used in parts which are injection moulded or extruded. Predominantly glass fibres are employed, although carbon fibres and asbestos are occasionally used. The effectiveness of the reinforcement relies on the stress in a component being transferred from the polymer (normally termed the matrix) to the fibre. Thus, a good bond is necessary between fibre and matrix, and to this end the glass is coated with a coupling agent which is compatible with the matrix in which it is dispersed. 

Careful attention must also be paid to the design of a mould, especially the 

Long-fibre composites are mainly used with hand lay-up systems using polyester or epoxides as the matrix in which glass fibres are suspended. It is possible in long-fibre composites to calculate the strength and stiffness more accurately using conventional composite theory. For example, in a unidirectional continuous fibre composite, the equation for the total stress, in the composite can be shown to be  

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