Motorsport Composite Fundamentals: Tow
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Tow
05.27
| 00:00 | This section of the course is all about understanding the different reinforcement materials used in the construction of composites, whether that's for fiberglass, carbon fiber, aramid or natural fiber composites. |
| 00:12 | Of course, the final composite itself is a material, but right now we're more interested in the ingredients that we'll use to make the composite. |
| 00:21 | Let's start with toe, which is essentially many individual fibers bundled together. |
| 00:25 | The toe is often wound into a roll or spools and can be used as is for reinforcement or converted into another form of reinforcement, like a woven fabric for example. |
| 00:37 | The word yarn is more typically used in the place of toe for kevlar or other aramid fibers. |
| 00:43 | Again, toe is used to create the fabrics we'll be discussing soon, but in this form it can also be used as local reinforcement. |
| 00:51 | An example of this would be joint binding, basically joining two composite parts together using toe as the reinforcement or wrapping it around structures to increase the strength. |
| 01:01 | Of course, it still needs to be combined with a resin matrix to construct a structural composite material. |
| 01:08 | Rolls or spools of toe are available in different lengths but the key differentiation is what's referred to as the sizing of the fibers and this will be carried over to the other forms of reinforcement that we'll discuss next. |
| 01:21 | For carbon fiber the most common sizings are 1k, 3k, 12k and 24k. |
| 01:28 | The k count represents the number of thousands of individual carbon fiber filaments that are bunched together to make up the toe. |
| 01:36 | For example for 3k the toe is made up of 3000 individual filaments. |
| 01:41 | The sizing or thickness of aramid yarns is typically described by its text count, where this will be the number followed by text and this represents the weight in grams per 1000 meters of yarn. |
| 01:55 | Just as common as decitex or detex which is the weight in grams of 10 000 meters of yarn. |
| 02:01 | So, for example 1610 detex would be 1.61 kgs per 10 000 meters and 3220 detex is twice the weight at 3.22 kgs per 10 000 meters. |
| 02:16 | This detex number might also be accompanied by a sizing value stating the amount of filaments in the yarn, just like for carbon fiber toe. |
| 02:24 | The imperial alternative for this is what's referred to as yield and represents the number of yards per pound. |
| 02:31 | For example 225 yield means that 225 yards of toe or yarn weighs one pound. |
| 02:40 | So, a larger value here is actually a lighter product, where a larger text value is a heavier product. |
| 02:47 | Chopped toe as the name suggests is short chopped sections of toe, the length of which is usually kept to a consistent value. |
| 02:54 | Chopped toe is often used as reinforcement for compression molded carbon fiber composites, commonly referred to as forged carbon. |
| 03:03 | It can also be used in hand laminating and resin infusion though, all of which we'll be discussing in more detail in the coming modules. |
| 03:10 | The final thing we'll discuss here is something that we've mentioned briefly before and that's gun roving or the use of a chopper gun. |
| 03:17 | Fiberglass roving is fed into a gun that simultaneously chops the fiber, mixes it with resin and using compressed air, sprays it directly onto the surface of the mold. |
| 03:27 | This greatly reduces the time required compared to the techniques laying up the fabrics that we'll be discussing soon. |
| 03:34 | So, it's ideal for industrial uses and applications like boat building. |
| 03:39 | However, while the random orientation of fibers does provide reasonable strength and stiffness in all directions, it naturally doesn't allow for much control over the mechanical properties. |
| 03:50 | When using directional or woven fabrics, the fibers can be aligned with the forces to optimise the strength and stiffness to weight ratios for specific applications, but we'll come back to this in the following module. |
| 04:02 | The appearance of the finished product is also a lot less consistent and controllable, so it's not really the ideal solution when aesthetics are important. |
| 04:12 | Polyester or vinylester resin is typically used here but we'll dig into this more in our next module covering non-woven mats and also our upcoming modules specific to resins. |
| 04:23 | In summary, tow is the primary form of fibers grouped together in a continuous roll or spool. |
| 04:29 | For aramid fibers, these are more commonly referred to as yarn. |
| 04:33 | Besides the different lengths of tow, the most important differentiation is the sizing, which for carbon fiber is typically expressed as the K value, being the number of thousands of individual fiber strands in the tow. |
| 04:47 | Fiberglass and aramid fibers can also be described by their text value representing their weight in grams per 1000 meters or yield representing the yards per pound. |
| 04:58 | Tow is useful for local reinforcement like joint binding but is also the primary form before the filament winding of the fabrics we'll be discussing in the following modules. |
| 05:09 | Fiberglass tow is also commonly used in a chopper gun where it's combined with polyester resin and sprayed directly onto the target surface. |
| 05:18 | However, the mechanical properties and appearance of these composites aren't well suited to high performance applications. |
