Things like Badminton rackets, Tennis rackets, golf clubs, softball bats and hockey sticks. I know its light and all but what are the other reasons why is it used as a stick to hit objects? Can someone give me a detailed answer? Edit: Is tensile strength an important factor to making these sticks if so why?
In: Engineering
TL;DR:
There’s three things you need to know about Carbon Fiber (CF):
1. It’s light, means swing faster, means can hit things with more energy.
2. It’s strong; either in one direction, or many directions. You can tailor the characteristics of the CF in one or more directions depending on the application.
3. It combines with other materials well. Compounded with the custom strength directionality, you can use resins or other materials to take advantage of their elastic, or rebounding properties to get out more energy than you put in. (Look at a [hockey stick flex in slow motion.](https://www.youtube.com/watch?v=IsCdywftyok))
Long, maybe an ELIgrade9 or ELIgrade10.
Review: There’s three things you need to know about Carbon Fiber:
1. It’s light.
2. It’s strong; either in one direction, or many directions.
3. It combines with other materials well.
1. Weight plays into a factor when looking at sports sticks that hit things like hockey sticks, badminton rackets, tennis rackets, baseball bats, golf clubs, etc., because the more weight you add, the harder it is to swing the stick. The easier it is to swing this stick, not only is it less effort, but you can also impart more *kinetic energy* into the object you’re hitting with the stick (ball, puck, shuttlecock). The equation for Kinetic Energy is:
`KE = 0.5 * mv2`
Where *m* is the mass of the object, *v* is the velocity of the object that is moving. The important part to focus on is the *v**^(2)* term, which is a product of the *SQUARE* of the velocity of the object. This means the faster you swing, the energy goes up like.. REALLY fast. For example, swinging a 2kg object at different speeds this is what you get:
|Object weight|Velocity|Kinetic Energy|
|:-|:-|:-|
|2kg|1 m/s|1 J|
|2kg|2 m/s|4 J|
|2kg|3 m/s|9 J etc… |
|3kg|1 m/s|1.5 J|
|4kg|1 m/s|2 J|
|5kg|1 m/s|2.5 J|
So as you can see, increasing the speed of the object increased the KE *much* faster than increasing the weight. That’s why head speed in golf is so crucial for maximum distance. (also why the longer clubs go farther, larger arc etc… that’s another ELI5 entirely)
2. Carbon Fiber is actually just that, it’s fibers of Carbon material, literally woven together like your rug, or t-shirt is. It can be woven in many different patterns for different applications. The reason this is important is because the strength is entirely dependant on the *axis* of the weave. If you place all your fibers in one direction ([uniaxial/unidirectional](https://www.speednik.com/wp-content/blogs.dir/1/files/2015/08/2015-08-27_22-31-54-640×427.jpg)), you have LOTS of tensile strength (which is where CF gets all its strength) in that one axis, but if you pull it apart in the other direction/axis, the fibers pull apart easily.
If you offset these axis by an angle, now you have [biaxial/bidirectional](https://www.speednik.com/wp-content/blogs.dir/1/files/2015/08/2015-08-28_20-47-09.jpg) CF. Now the material is strong in two directions, typically offset 90 degrees from one another. You’ll likely recognize it, as this is the most common “print” you can find on vinyl wraps, hydro dips, or other fake CF prints.
There are more complex weaves (twills) that go into lots of details ripe for PhD research if you’re so inclined. The other cool looking one is “[forged](https://vinzers.com/wp-content/uploads/2018/11/forged_s9.jpg)” CF, or chopped CF. Unfortunately, it’s not forged in the traditional sense. Oftentimes it’s created purely for an asethetic as the top layer that shows, and doesn’t serve any significant structural purpose (AFAIK) due to the non-continuous fibers. It will also likely have a much worse strength/weight ratio, as pure “forged” CF will have a higher density of resin.
3. CF is oftentimes referred to as a “composite” material, because it is. It is composed of many types of material, for instance you could have a “forged” CF top layer, two layers of uniaxial CF wrap, two more twill layers, and finishing off with two bi-axial, 45-degree offset layers. You’ve just created a composite sandwhich of Carbon fiber layers! However, if you don’t add any bonding agent to this roll of CF, the hockey stick you tried to build will be floppy. You don’t be hittin any dingers, or sniping any pockets with a wet noodle, now would ya bud?
This is where the resin comes into play. It is the bonding agent that gives CF objects the *compressive* strength. It also contributes to the elastic strength a little as well, depending on the selected resin. You can also mix in a few different resins while you build, or *layup,* the carbon object you’re building. The first layer to go down will likely be a UV-resistant overcoat resin that will protect the outside of the part. Next, maybe you’ll use something like a quick-set resin to get that layup a stiffy before you take a break that night. To finish it off, there’s a few tricky bends and bubbles you want to squeeze out so you use a long-set resin to really make sure that the final structure is perfect.
So, as you can see, the CF product of any type is a gentle massage of getting many different materials of various abilities to work together, not just the Carbon Fiber.
My favorite use of CF in my personal life is [my hockey stick](https://www.frontierhockey.com/images/portfolio/f11.1/f11.1-shaft-radius-large.jpg). It’s largely a rectangle with rounded corners and concave long sides, which makes it easy to hold in the hand, very comfortable, and the concave shapes give the shaft a little more stiffness while retaining the ultra-light structure. The best part I can’t find a picture of, but the shaft tapers down to an elliptical near the blade, which isn’t as stiff as the rectangle meaning the stick is very stiff uptop, but soft and playful down low. This complements quick loading for ultra-fast releases on shots, to catch an unsuspecting goaltender off guard. This is the sort of material manipulation you can only get using the miracle that is Carbon Fiber, or VERY expensive processes thinning walls and using generative design + 3D printers and metal.
Hopefully someone enjoyed. I had a great time chatting about this with myself, so thanks for the ELI question!
Latest Answers