When understanding carbon fiber products, many people see products with carbon fiber texture as the first feeling that they are cool, with a sense of fashion and technology. Therefore, there are many products that pursue the appearance of carbon fiber texture. The carbon fiber sticker that appears the most on Taobao.com is a carbon fiber sticker. This is a sticker printed with carbon fiber texture, which has nothing to do with carbon fiber. However, using carbon fiber patterns as decorations is overkill. In fact, under the small lines of carbon fiber, there are huge secrets. Today we will discuss the difference between different carbon fiber textures to make carbon fiber products.
First of all, we know that when carbon fiber is manufactured, it is not produced one by one, but one by one. Then the number of carbon fibers contained in each bundle may be somewhat different, but it can usually be divided into 1000 and 3000. , 6000 roots, 12000 roots, which are the familiar concepts of 1k, 3k, 6k, 12k and so on.
Carbon fiber usually comes in the form of a woven fabric, which makes it easier to use and can provide additional strength depending on the application. Therefore, there are many weavings used for carbon fiber fabrics. The most common are plain weave, twill weave and satin weave, we will introduce them in detail respectively.
The plain weave carbon fiber board looks very symmetrical and has a small checkerboard style appearance. In this weaving, the tow is weaved in an up/down pattern. The interval between the interlaced tows is very small, so that the plain weave has high stability. The stability of a fabric is the ability of the fabric to maintain its weaving angle and fiber orientation. Due to its high stability, plain weave is not suitable for laminates with complex contours, and it will not be as flexible as some other weaves. Generally, plain weave fabrics are suitable for the appearance of flat panels, tubes and 2D curved structures.
One disadvantage of this weaving pattern is that because the distance between the weaves is very short, the crimp in the tow is very large (the angle formed by the fibers during weaving, see the figure below). This kind of bending will produce stress concentration, which will weaken the strength of the part over time
Twill weave is a kind of weave between plain weave and satin weave. We will discuss satin weave below. Twill fabric has good flexibility, can be formed into complex contours, and is worse than satin weave in maintaining fabric stability, but not as good as plain weave. If you follow a tow in a twill weave, it will go up through a certain number of tows and then go down through the same number of tows. The upper/lower pattern will form the appearance of diagonal arrows, called “diagonal lines”. Compared to plain weave, the distance between drag and stagger is longer, which means less crimping and less potential stress concentration.
2×2 twill is probably the most well-known carbon fiber weave in the industry. It is used in many appearance and decorative applications, but also has excellent functions, it has moderate formability and moderate stability. As the 2×2 name implies, each tow will go down through 2 tows and then go up through 2 tows. Similarly, the 4×4 twill will go down through 4 tows and then come up through 4 tows. It has slightly higher formability than 2×2 twill because the weave is not so tight, but the stability is also lower.
Satin weaving has a long history in fabrics, and was used in the early days to make silk fabrics with excellent drape properties, while also looking smooth and seamless. For composite materials, this drape means that it can easily form and wrap complex contours. Due to the easy formability of the fabric, its stability is low. Common satin weaves include 4-wire satin (4HS), 5-wire satin (5HS) and 8-wire satin (8HS). As the number of satin weaves increases, the formability will increase and the fabric stability will decrease.
The number in the name of the wire harness satin weave indicates the total number of tows passing upwards and passing downwards. For 4HS, it will be more than 3 tows upwards, and then through 1 tow downwards. For 5HS, it will have more than 4 tows up and then 1 tow down, while 8HS will pass 7 tows up and then 1 tow down.
Stretched tow and standard tow
Unidirectional cloth carbon fiber has no bending state and can bear the force very well. The woven cloth tow needs to be bent up and down in the orthogonal direction, and the strength will drop greatly. So when the fiber tow is woven up and down to form a fabric, the strength is reduced due to the crimp in the tow. When you increase the number of tows in the standard tow from 3k to 6k, the tow becomes larger (thicker) and the bending angle becomes larger. One way to avoid this situation is to unfold the filaments into wider tows. This is called unfolding the tow, and the resulting cloth is also called spreading cloth. This has many advantages.
The crimp angle of the widened tow is smaller than the weave angle of the standard tow, thereby reducing cross defects by increasing the smoothness. A smaller bending angle will result in higher strength. Compared with unidirectional materials, spread tow materials are also easier to use and still have fairly good fiber tensile strength.
Unidirectional cloth industry is also called UD cloth. As the name suggests, uni means one, and all fibers face the same direction. This gives unidirectional (UD) fabrics some high-strength advantages. UD fabric is not a woven fabric, there is no crimped interwoven tow. Only highly oriented continuous fibers can increase strength and stiffness. Another advantage is the ability to control the strength of the product by adjusting the layup angle and the layup ratio. The use of unidirectional cloth to optimize the ply structure of the bicycle frame to adjust the performance is a good example. The frame must maintain rigidity and rigidity in the bottom bracket area to transmit the driver’s power to the wheels, but the frame also needs to have a certain degree of flexibility and flexibility. With unidirectional cloth, you can choose the precise direction of the carbon fiber to obtain the desired strength.
One of the main disadvantages of unidirectional cloth is poor operability. Unidirectional cloth tends to spread easily during the laying process because it has no interwoven fibers to hold it together. If the fibers are not placed correctly, it is almost impossible to reposition them correctly again. Unidirectional cloth cutting can also cause problems. If there are any fibers pulled up in a particular part of the cut, those loose fibers will be pulled up to the entire cloth surface. Generally, if you choose unidirectional cloth for layup, use plain weave, twill weave, and satin weave fabric for the first and last layers to help improve workability and part durability. In the middle layer, a unidirectional cloth is used to precisely control the strength of the entire part.
Post time: Jun-30-2021