In a polymeric composite term, a fabric can be defined as the manufactured assembly of the long fibers of aramid, glass or carbon, or the combination of all these so as to produce a flat sheet or more layers of fibers. The layers may be held together by mechanical interlocking of fibers themselves or by the secondary materials which bind them together and hold them in place, giving it sufficient integrity to be handled. The types of fabric are grouped together by the orientation of the fibers used, and also by construction methods used to hold them together.
There are four main types of fabric; which includes unidirectional, multiaxial, woven and random fabric.
These types of fabric are one which has its majority of fibers running in one direction only. Some small fibers or other secondary materials may run in the opposite direction with an aim to hold the primary fibers in position, though other fibers may offer some structural properties. The unidirectional fabrics always have its primary fibers in zero degrees direction but also can have them at 90 degrees to roll length.
Unidirectional fabrics offer an ability to place the fiber in the component exactly where it is supposed to be and in optimum quantity as well. These type of fabric are crimped and always straight, this results from the highest fiber properties from the fabric in composite component constructions. With the mechanical properties, the unidirectional fabrics can be improved by a prepreg unidirectional tape, whereby there are no secondary materials holding the unidirectional fibers together. With this prepreg product, the resin system only holds the fibers together.
There are different methods which can be used to maintain the primary fabric together including stitching, weaving, and bonding. The drape of the fabric is primarily controlled by construction style, while its area weight is determined by selecting the appropriate combination of the fiber tex and fibers per cm.
Woven fabric is made by the interlacing of warp fibers and weft fibers in a weave or regular style. Fibers integrity is maintained with mechanical interlocking. The drape, stability and surface smoothness of fabric is primarily controlled by weave style. Here are some of the common weave style.
In plain weave style, the warp passes alternately over and under each weft fiber. The fabric seems symmetrical with reasonable porosity and good stability. With high tex this weave gives excessive crimp and therefore can’t be used for heavy fabrics.
These are fabric with warp fiber alternately weave over and under the weft fiber with several repeated manner. It has superior wet out and the drape is seen over the plain weave. The fabric has a smooth surface and a slightly high mechanical property.
These are twill waeve styles which are modified to produce less intersection of weft and warp. Harness number used in designation is the total number of the fiber crossed and passed under, before it repeats the pattern. The satin weaves are flat, have high degree of drape and have good wet out. Its low crimp gives a good mechanical properties. They can produce fabric with a tight weave.
Hybrid Fabric Type
Hybrid refers to fabric that has got one or more type of the structural fiber in its made. If in multi-layer laminate, the properties of more than fiber is required and therefore it will be possible to provide it with two fabrics each containing the kind of fiber needed. However, in low weight laminate, the hybrid fabric allows the two fibers to present in one layer instead of two. It will be even possible for one fiber running to weft direction while the other running to warp direction. The common combination of hybrid fabric includes.
- Aramid/ carbon
The tensile strength and high impact resistance of carbon fiber combines with the high compressive strength of aramid. Both of the fabrics have got low density and relatively high cost.
- Aramid / glass
The high impact, tensile strength and low density of the aramid fiber combines with a tensile strength and good compressive of the glass, but also has relatively high cost.
- Carbon/ glass
The carbon fibers contribute relatively to a high tensile, stiffness, compressive strength and reduced density, while the glass reduces the cost
In the past years the multiaxial fabric have find favor in construction of composite component. The fabric consist of many layers of long fibers held together by secondary stitching tread. Its main fibers can be any of its structural fiber available in combination. The stitching tread is always polyester because of the combination of appropriate fiber orientation and the cost. The most common form of these multiaxial fabrics are;
Weave and stitch
With this method the -45 degrees and +45 degrees layers are produced by weaving the weft unidirectional and skewing the fabric using a machine to 45 degrees. The weft unidirectional or warp unidirectional can be used to skew fabric to zero degrees and 90 degrees. Due to fact that the heavy roving can be used in making every layer the weaving process will be relatively faster.
The simultaneous stitch process can be done in two special machines based on its knitting process, like the one made by Malimo, Liba, Mayer, and so on. Every sewing machine varies in precision with which fibers are laid, especially in reference to keeping the fibers parallel. This kind of machine has a frame which draws fiber for every axis, till the required set is being assembled, then stitch together.
In the recent years, human have known how to make their own fibers, primarily from 2 sources. The first source is by dissolving cellulose in cell walls of the plants and reforming them into treads, this was discovered by Rayon, since the cellulose are the primary constituent of the wool fiber, we are reinventing just the wheel.
The second source is by synthesizing the cellulose like molecules from oils example are polyester and nylons. The synthesizing forms are quite flexible and often very poor in breathing and hence they should always be mix with cotton.
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