Beginners Guide: Fabric Weaves for Composites
When talking about composites, it is important to remember that the material you are working with is fiber dominant. This means that when combining the fiber material and resin, the resulting composite part will largely take on the properties of the fiber material.
So what does this mean for fabricators? In the simplest terms, the fiber you decide to use will have a huge impact on your finished product.
Before starting any project, fabricators must first decide which reinforcement has the properties that best suit their project. Will Fiberglass work? Is the added strength that comes with Carbon Fiber necessary? Will the ultimate impact and abrasion resistance from Kevlar be needed?
Simply choosing your reinforcement isn’t the end of your planning. Once you’ve decided on a fiber, you must then decide on the form of the reinforcement. This can refer to a few different factors, such as fabric count, and weave style.
Fabric Thread Count
Fabric count refers to the number of warp and fill fibers per inch of your fabric. If you look at a roll of fabric, some of the fibers run in the direction of the roll and are continuous for the entire length of the roll. These fibers are known as the warp and are often referred to as ends. The shorter fibers that run crosswise along the width of the fabric are known as fill, and are often referred to as picks.
For an example, a 24 x 22 fabric has 24 ends in in every inch of fill direction, and 22 picks in every inch of warp direction. Note that you count warp fibers in the fill direction, and vice versa.
For most fabrics, you will find a variety of weaves that each serve a particular purpose. These weaves all behave differently, and it is important to look through your options before choosing one for your project. What one weave might be great at, a similar weave could perform very poorly at and vice versa. It’s important to know and understand these characteristics before you start laying down fabric!
Plain Weave Fabric
Plain weave fabric is one of the most common types of weaves you will find in composites. In a plain weave fabric, the warp and fill fibers interlace at every crossing, with the fibers alternating passing above and below each other.
A plain weave fabric will be very stable, and offer strength equally in both directions. However, when using a plain weave fabric it is important to keep in mind that it will not conform to complex shapes with ease (or, at times, even at all!)
Twill Weave Fabric
In a twill weave, one or more fibers alternately pass over and under a designated number of fiber bundles. For example, a 2 x 2 twill weave will have fibers that pass over two bundles, then under two bundles, throughout the length of the fabric. Adjacent parallel fibers are offset by one fiber bundle which creates a “herringbone” pattern throughout the fabric.
This open weave allows the twill weave fabric to have easier conformity to complex shapes, and makes it popular for cosmetics. This style retains a balance in both sides of the fabric.
Satin weave fabric is constructed in such a way that a fiber bundle passed over a designated number of bundles (determined by the particular weave) and then under one bundle repeatedly. The total number of fibers involved is referred to as the “harness.”
In a 8-harness satin weave fabric, a fiber bundle will pass over seven bundles, then under one, over and over (7+1=8, thus why we call it a 8-harness.)
For satin weaves, this producted a much flatter fabric that is easily used to form complex shapes that even twill weave might struggle to obtain. Satin weaves will deliver a slight edge in strength over its plain and twill weave counterparts, but this form of fabric is unbalanced.
This means that one side of the fabric will be mostly warp or fill, while the other will be the opposite. Fabricators usually have to invert half of the piles within a lamination in order to produce a symmetrical part.
A basket weave is essentially a plain weave with, rather than one-over-one interlacing, two or more warp fibers interlace with two or more fill fibers. As you might have guessed, that would be known as a 2 x 2 basket weave.
Basket weaves do not need to be symmetrical, it is possible to have an 8 x 2 basket weave, depending on your needs. Basket weaves are flatter and slightly stronger than plain weaves, but are less stable.
Leno and Mock Leno Weave
Less used, the Leno refers to a form of plain weave fabric in which adjacent warp fibers are twisted around consecutive fill fibers in order to form a spiral pairing. This effectively locks the fill fibers into place within the fabric.
This type of fabric is often used in conjunction with other fabrics, as the open weave style does not generally produce an effective composite.
Mock Leno weaves are another version of a plain weave fabric in which occasional warp fibers, at regular intervals but usually sever fibers apart, deviate from the alternate under-over interlacing and instead interlace every two or more fibers.
This happens with similar frequency in the fill direction, and the overall effect is a fabric with increased thickness and a rougher surface.
Patterned weaves refer to weaves that are more specialty and do not have a widely known industry specification. Because they are not widely known, it can be difficult to determine their physical properties. The particular pattern style will have a cosmetic feature, such a cool or interesting pattern, but said pattern will also have an effect on the fabrics characteristics.
For example, our #3222 Wasp – 3K, 12×18 Carbon Fiber Fabric has a hexagon pattern that will give parts a honeycomb or reptile scale like finish. Because of this pattern, the #3222 has a heavier filling density which will ultimately offer a higher tensile strength in the fill axis.
For more information on The Strengths of Patterned Carbon Fiber, please visit our learning center.
When working with reinforcements, you will often notice style numbers. These numbers refer to specific fabrics that have a set weave, weight, and end/pick ratio that fabricators can rely on. As an example, a Style 7781 E-Glass will always be a 9-ounce-per-square-yard, 57 x 54, 8-harness satin weave fiberglass fabric. For reference, FibreGlast’s Style 7781 E-Glass can be found on our website under part number #543.
Finally, there are a number of products on our website known as “stitched fabrics” These fabrics consist of several layers of unidirectional fibers in different orientations, including 0 degrees, 45 degrees and 90 degrees. Fibers are stitched rather than woven together, which helps to avoid crimping and make for increased fiber strength for parts. In practice, these fabrics will be handled in much the same way as woven fabrics.
Looking for more information on reinforcements? Be sure to look at our other blog posts, such as the Different Grades of Kevlar, Carbon Fiber vs Fiberglass, as well as our guides on Choosing the Right Resin and Polyester vs Vinyl Ester Resins. You can also find more information in our Learning Center, such as our white paper on Reinforcements, The Fundamentals of Fiberglass and The Strength of Patterned Carbon Fiber.
Any other questions? Let us know in the comments section below. Be sure to check out our Facebook, and follow us on twitter @Fibreglast for more information the composites industry.