Introduction to composites
Effect of fibre length on composite properties
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Does size really matter? ..........
....the effect of fibre length on composite properties....
Conventional fibre reinforced thermoplastic composites are generally reinforced with short fibres up to 3mm long. Even long fibre compounds have a maximum fibre length of 10mm. Imhotep Ltd uses continuous fibres. Does this matter?
When a fibre embedded in a matrix is subjected to a tensile load parallel to the fibre, the applied stress on the matrix will be transferred to the fibre across the interface. The tensile stress in the fibre is zero at the fibre ends and increases along the fibre length to a maximum in the centre, conversely the shear stress in the interface is a maximum at the fibre ends reduces to almost zero in the centre. The rate of stress build up along the length of each of the fibres is dependent on the adhesion between fibres and matrix and their elastic properties.
To achieve the maximum stress in the fibre the fibre length must be greater than the critical length, Lc.e.g. For Polypropylene glass Lc » 1.8mm
Therefore, the efficiency with which the fibres stiffen and reinforce the matrix decreases as the fibre length decreases as a greater proportion of the fibre length is not fully loaded.
Therefore, for mechanically efficient composites you want the fibres to be as long as possible as illustrated below:
.......Yes, size does matterTo find out how we have made use of this technology click on the buttons in the contents list on the left.
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Imhotep Ltd's articles on thermoplastic composites and their new technology:
Eureka article Materials World article PRW article back to top
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