Re: Difference between Chopped mat and woven fiberglass mat?
From West Systems website:
CHOPPED STRAND FIBERGLASS MAT . This material is just what the name implies. The fibers are typically 3-4 inches in length and are randomly oriented. Chopped strand mat is not a very strong material because of the short fiber length. However, it is isotropic. This means that it is equally strong in all directions. Mat and fillers are the only composite reinforcements exhibiting this trait. This is the least expensive reinforcement form and is thus the most widely used. It is suitable for molds and part production. The random orientation effectively hides fabric print through of gelcoats and makes molds which are equally stiff in all directions. It should be noted that chopped strand mat is only compatible with polyester resin.
WOVEN FABRICS. Woven fabrics are strong reinforcements because the fibers are bundled into yarns oriented in just two directions. The warp and fill yarns run at 0 and 90 degrees respectively. Thus, fabrics are anisotropic, or strong in only two directions. Fabrics need to be oriented so the fiber yarns run parallel to the expected loads. If extra strength is needed in a different direction, another ply must be added at an angle to the first. The most common angles are +/- 45 degrees.
Styles Of Woven Fabrics
There are many styles of woven fabric to choose from. The most common are the plain weave fabrics where the warp and fill threads cross alternately. Plain woven fabrics are generally the lease pliable, but are easy to cut and handle because they dont unravel badly. However, their strength is compromised due to the severe prebuckling already present in the fabric. As stated under tows, fibers only produce their greatest strength when they are perfectly straight. The frequent over/under crossing of the threads reduces the strength of plain weave types, though they are still adequate for all but the highest performance applications.
Twill weaves and satin fabrics are highly pliable and stronger than the plain weave styles. In a satin weave, 1 filling yarn floats over 3-7 other warp threads before being stitched under another warp thread. Threads run straighter much longer in this loosely woven type, maintaining the theoretical strengths of the fiber. Obviously, pliability is higher and these fabrics conform easily to complex shapes. Once cut, however, they can unravel easier because each thread is not held as tightly. Twill weaves offer a compromise between the satin and plain weave types, as well as an often desirable herringbone cosmetic finish.
