Fibres length

Tracheid length declines by 0.75 mm in going from the north to the south of New Zealand, being influenced by simple variables of latitude, altitude, temperature and rainfall. 

These trends are valid for many species both hardwoods and softwoods. Bao et al. (2001) found for seven softwoods that tracheid length in corewood was 21-52% shorter than in outerwood, and for the three hardwoods studied the fibres were about 24% shorter in corewood. 

For over 40 years there have been intense efforts to develop improved eucalypt hybrids for 7 yr-old pulpwood crops. Elite clones of E. urophylla x grandis have both desired long fibre characteristics, i.e. long for a hardwood, and less variation despite consisting solely of variable corewood  

Short rotation hardwoods have a high lignin content in part beeause the wood in a 5-7 yr pulp rotation consists entirely of corewood. 

There is interest in the trade off between volume produetion ( 40 m /ha/yr) and an increased basic density as a higher density means more fibre in the digester and so more pulp production. This could be achieved by crossing another species with the traditional E. urograndis hybrid. 

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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... 

Process Temperature range Fibre length Fibre outer diameter... 

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... 

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. 

Normal The LVEDP may be used as a measure of preload or initial fibre length . Cardiac output increases as LVEDP increases until a maximum is reached. This is because there is an optimal degree of overlap of the muscle filaments and increasing the fibre length increases the effective overlap and, therefore, contraction. 

Figure 6.1. (a) Schematic curve of performance versus fibre length (b) Schematic curve of performance versus fibre level... 

Use of a coefficient /3 determined by experiments according to the fibre lengths... 

Grades reinforced with fibres 20 mm and more in length cannot be processed on conventional equipment. It is necessary to use, for example, the extrusion-compression technique. The process differs too much from conventional injection used for short glass fibre reinforced thermoplastics to measure the influence of fibre length alone. 

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