Fibres fibre length

For many applications (e.g. body pressings), it is inconvenient to use continuous fibres. It is a remarkable feature of these materials that chopped fibre composites (convenient for moulding operations) are nearly as strong as those with continuous fibres, provided the fibre length exceeds a critical value. 

It is evident from Fig. 3.29 that there is a minimum fibre length which will permit the fibre to achieve its full load-carrying potential. The minimum fibre length in which the maximum fibre stress, ((rf)maxt be achieved is called the load transfer length, The value of may be determined from a simple force balance... 

The maximum value of it will occur when (tensile strength of the fibre, Ofu, and this is defined as the critical fibre length, Ic... 

Example 3.17 Short carbon fibres with a diameter of 10 fim are to be used to reinforce nylon 66. If the design stress for the composite is 300 MN/m and the following data is available on the fibres and nylon, calculate the load transfer length for the fibres and also the critical fibre length. The volume fraction of the fibres is to be 0.3. 

The average fibre stress, area under the stress/fibre length graph by the fibre length. 

In a short carbon fibre reinforced nylon moulding the volume ffacdon of the fibres is 0.2. Assuming the fibre length is much greater that the critical fibre length, calculate the modulus of the moulding. The modulus values for the fibres and nylon are 230 GN/m and 2.8 GN/m respectively. 

Milled Fibres These are finely ground or milled fibres. Lengths range from 30... 

Short Chopped Fibres These are fibres with lengths up to about 6 mm. The fibre (L/D) ratio is typically about 800. They are more expensive than milled fibres but provide better strength and stiffness enhancement. 

Long Chopped Fibres These are chopped fibres with lengths up to 50 mm. They are used mainly in the manufacture of SMC and DMC (see Section 4.10.2). 

Process Temperature range Fibre length Fibre outer diameter... 

Fibre means length >5pm, average diameter <3pm and length dia ratio >3 1. 

Important parameters, characterizing fibre properties, are the attenuation a and numerical aperture NA. The attenuation (Equation 1) represents optical losses caused by absorption or scattering of the light guided through the unit fibre length. It is given by ... 

Man-made fibres produced as continuous filaments and then cut into short lengths to match those of some natural fibres such as cotton or wool. The staple of cotton, wool, staple fibre, etc., is an indication of the average fibre length. Stark Rubber... 

It is assumed that all chains are oriented parallel to the fibre axis and that equal parts of the fibre contain equal numbers of starting points of chains of arbitrary length u. Thus the starting points are distributed homogeneously along the length of the fibre. The length distribution of the chains is determined by the distribution function /( ) with... 

The number of chains M that pass through a cross section of the fibre can be expressed in the chain volume Vc of the fibre. Let the cross section of a chain be Ac, then the N starting points of chains per unit length of the fibre yield a volume contribution c0NwaAc. The chain volume in a part of the fibre with length I and cross section D becomes c0NwaAcL, which gives a chain volume fraction... 

Figure 4.1 Sheet structures arising from (a) the random distribution of 970 straight fibres of uniform length, (b) a photomicrograph of a 2.5gmr2 sheet of paper in which the mean fibre length and density correspond to that...

Chen, F. and Jones, F. R Injection moulding of glass fibre reinforced phenolic composites 1. Study of the critical fibre length and the interfacial shear strength, Plast.. Rubber Composites Proc. Appl., 23, 241 (1995). 

Fukuda, H. and Chou, T. W A probabilistic theory of the strength of short-fibre composites with variable fibre length and orientation,. /. Mater. Sci., 17, 1003 (1982). 

The strength of cardiac contraction is dependent upon the initial fibre length. 

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