Carbon fiber textures from a performance point of view
The first feeling of carbon fiber products is cool, with a sense of fashion and technology. There are many products that pursue the appearance of carbon fiber texture. In fact, the time road of carbon fiber contains a huge secret. Today, let's discuss the difference between different carbon fiber textures when we make carbon fiber products.
First of all, we know that when carbon fibers are manufactured, they are not produced one by one, but bundles of bundles, so the number of carbon fibers contained in each bundle may be somewhat different, but it can usually be divided into 1000 and 3000. , 6000, 12000, that is, we are familiar with the 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 work with and can provide additional strength depending on the application. Therefore, there are many weaves for carbon fiber fabrics. The most common are plain weave, twill weave and satin weave, which we will detail separately. The plain weave plain carbon fiber panels look symmetrical and have a small checkerboard-inspired look. In this weaving, the tow is woven in an up/down pattern. The spacing between the interlaced tows is small, giving the plain weave high stability. Fabric stability is the ability of a fabric to maintain its weave angle and fiber orientation. Due to its high stability, plain weave is less suitable for laminations with complex contours and it will not be as flexible as some other weaves. In general, plain weave fabrics are suitable for the appearance of flat sheets, tubes and 2D curved structures.
Twill is a weave between plain weave and satin weave, which we will discuss below. Twill has good flexibility, can be formed into complex silhouettes, and is worse than satin weave at maintaining fabric stability, but not as good as plain weave. If you follow a tow in a twill weave, it goes up through a certain number of tows and then goes down through the same number of tows. The over/under pattern creates the appearance of diagonal arrows called "twill lines". Compared to plain weave, the longer distance between drag interlaces means less crimp and less potential stress concentration.
2x2 twill is probably the best known carbon fiber weave in the industry. It is used in many exterior and decorative applications, but also has excellent functionality, it has moderate formability and moderate stability. As the 2x2 name suggests, each tow will go down through 2 tows and up through 2 tows. Likewise, a 4x4 twill will go down through 4 tows and come up through 4 tows. It has slightly higher formability than 2x2 twill because the weave is less tight, but the stability is also lower.
Satin weave has an early history in fabrics, and was used to create silk fabrics that had excellent drape while also looking smooth and seamless. For composites, this drape means it can easily form and wrap complex contours. Due to the easy formability of the fabric, its stability is low. Common harness satin weaves are 4-strand satin (4HS), 5-strand satin (5HS) and 8-strand satin (8HS). As the number of satin weaves increases, formability will increase and fabric stability will decrease.
The number in the tow satin name indicates the total number of tows that pass up and down. For 4HS it will go over 3 tows up, then 1 tow down. For 5HS it will go over 4 tows up, then 1 tow down, while 8HS will go over 7 tows up, then 1 tow down. it is also less stable.
Spread Tow and Standard Tow
The unidirectional carbon fiber has no bending state and can bear the force well. The woven fabric tow needs to be bent up and down in the orthogonal direction, and the strength will drop greatly. So when the fiber tows are woven up and down to form a fabric, the strength is reduced due to the crimps in the tows. When you increase the number of tows in a standard tow from 3k to 6k, the tow gets bigger (thicker) and the bend angle gets bigger. One way to avoid this is to spread the filament into wider tows, this is called spread tow, and the resulting cloth is also called spread, which has many benefits.
The crimp angle of the stretched tow is smaller than the braid angle of the standard tow, thereby reducing crossover defects by increasing the smoothness. Smaller bending angles will result in higher strength. Spread tow materials are also easier to work with than unidirectional materials and still have reasonably good fiber tensile strength.
Unidirectional cloth is also called UD cloth in the industry. As the name suggests, uni means one, and all fibers are oriented in the same direction. This gives unidirectional (UD) fabrics some high strength advantages. UD fabrics are not woven fabrics, there are no crimped interwoven tows. Only highly oriented continuous fibers can increase strength and stiffness. Another benefit is the ability to control product strength by adjusting the ply angle and ply ratio. Bicycle frames use unidirectional fabrics to optimize the layup structure to adjust performance is a good example. The frame must maintain stiffness and stiffness in the bottom bracket area to transfer the rider’s power to the wheels, but the frame also needs to have some flexibility. With unidirectional cloth, you can choose the precise orientation of the carbon fiber to get the strength you need.
A major disadvantage of unidirectional cloth is poor maneuverability. Unidirectional fabric tends to unravel easily during layup because it has no interwoven fibers to hold it together. If the fibers are not placed correctly, it is nearly impossible to reposition them correctly again. Unidirectional cloth cutting can also cause problems. If any fibers are pulled up in a particular area of the cut, those loose fibers will be pulled all the way through the fabric. Typically, if a unidirectional fabric is chosen for layup, plain, twill, and satin weave fabrics are used for the first and last layers to help improve processability and part durability. In the middle layer, a unidirectional cloth is used to precisely control the strength of the entire part