Shortest fibre that could be spun is 15 mm . But the fibre  to be composite should be minimum  30 to 40 mm. These fibre should have the linear chain molecules with minimum Degree of ploymerisation  more than 300  DP .  High length to width ratio is important fiber characteristic s one should look for 

Please have  look at important fibre kevlar . Important fibre composite used in making technical Textiles. This fibre has revolutionized defense Textiles and produced smart applications to be used by the scientist 

Dear Srinivasa,

I think you can find the answer to your question in http://www.virginia.edu/bohr/mse209/chapter17.htm. Please find enclosed a short extract:

"Normally the matrix has a much lower modulus than the fiber so it strains more. This occurs at a distance from the fiber. Right next to the fiber, the strain is limited by the fiber. Thus, for a composite under tension, a shear stress appears in the matrix that pulls from the fiber. The pull is uniform over the area of the fiber. This makes the force on the fiber be minimum at the ends and maximum in the middle, like in the tug-of-war game.

To achieve effective strengthening and stiffening, the fibers must be larger than a critical length lc, defined as the minimum length at which the center of the fiber reaches the ultimate (tensile) strength sf, when the matrix achieves the maximum shear strength tm:

    lc = sf d /2 tm

Since it is proportional to the diameter of the fiber d, a more unified condition for effective strengthening is that the aspect ratio of the fiber is l/d > sf /2 tm."

Besides, please find enclosed an old but interesting lecture: http://pac.iupac.org/publications/pac/pdf/1985/pdf/5711x1651.pdf

I hope this may be helpful.

Dear Srinivasa Prakash Regalla,

Some time ago I was dealing with these two categories of products, maybe the following information can be helpfully for you.

Please consider that to obtain polymers reinforced with “short” glass fibres (GF), traditionally is used the melt-blending of the polymer matrix in twin-screw extruders with chopped GF (4-5 mm) or even with a roving of GF, step followed by the processing by injection molding. Following the melt-compounding in twin-screw extruders, due to the high shearing process, the length of glass fibres is low/ usually in the range 0.2-0.4 mm on the items performed by injection molding, thus this kind of reinforcing is traditionally called with “short fibres”. The polymers reinforced with “short” glass fibers are between the most commercialized, and I suppose that there is the case of your ABS-GF product.

On the other hand, you will find many papers regarding this subject (I will give only two examples http://onlinelibrary.wiley.com/doi/10.1002/pc.10412/pdf and http://onlinelibrary.wiley.com/doi/10.1002/pc.21217/epdf).

In the case of polymers reinforced with “long fibres” please consider that is used a kind of pultrusion process as technology that will allow to increase the percentage of fibres at 50 wt-% or even more, while keeping the length of the roving. In this case, the length of granules used for the processing by injection molding is about 10-15 mm, which will allow obtaining finally for the injection molded items a final length for the GF about ten times higher than using “short” fibres. The mechanical properties (tensile strength, impact resistance, rigidity, etc.) are significantly higher using polymers reinforced with “long” fibers, whereas the processing by injection molding becomes a little bit more difficult. For more information please consider the LNP™ VERTON™ Compounds: (https://www.sabic-ip.com/gep/Plastics/en/ProductsAndServices/ProductLine/lnpverton.html)

But I will refrain here my comments/answers…

So, go away with your research/product and good luck,

Marius

https://www.sabic-ip.com/gepapp/Plastics/servlet/ProductsAndServices/Product/series?sltPrdline=LNP VERTON&search=Search#searchresults

There is no arbitrary definition of "short fiber". Fiber length distribution in injection-molded thermoplastic parts depends on the original fiber length, the compounding process, the part geometry and the injection-molding process. The term is generally used in opposition to "long fiber" typically describing composites made with continuous fibers. Actual fiber lengths in molded parts may range from 0.1 mm up to about 2 mm.  

Dear Srinivasa,

If your question is remaining in actuality, just I saw the information about "The Long and Short of It: VLF (Very Long Fiber)" webinar — available following RTP Company site:

http://web.rtpcompany.com/info/webinars/long-fiber.htm

To have access, you need to give some general information about your interest.

With my best regards,

Marius

PS: See you also

http://www.rtpcompany.com/technical-info/molding-guidelines/long-fiber-compounds/comparison-of-long-short-fiber-pellets/

and

http://www.rtpcompany.com/products/structural/glass-fiber-reinforcement/

http://web.rtpcompany.com/info/webinars/long-fiber.htm

http://web.rtpcompany.com/info/data/long/

Any new fibre  composite strength multiplies due to the bonding force between  fibre and resin.Bond formation depends on  FTIR test  and it will give the exact  chemical structure and its strength.  Fibre length will not matter in this new composite but  linear chain molecule  should be anisotropic and should form perfect  bond with resin. Here fibre is not going for spinning weaving or knitting. It forms composite by Non woven techniques.  New covalent bond between resin and fibre determines strength of the Non woven. 

Sorry, I am adding a question here,

To calculate critical fiber length, we need matrix-bond strength (tm).

lc = sf d /2 tm ,

But how one can find matrix-fiber bond strength before compounding.

Aspect ratio is more appropriate factor characterizing the short and long fibers.

I have read somewhere that long fibers have aspect ratio of more than 800.

I agree with Dr Jose Manuel Menendez Martin