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This method has several strong points. It gives you control of the resin : to fabric ratio, has far less prep work, and needs the least amount of equipment.
However, it is also possibly the most messy messiest method, and many times there will be more resin that is needed - effectively deadweight as it no longer helps strengthen the part considerably.
Video of a wet layup: https://youtu.be/cj26c3V54SQ
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This method requires a good amount of setup work but doesn’t really require too much specialized equipment. It also ensures an excellent surface finish as typically, there will be more resin that than necessary and thus the part will resemble a laminate table. However, the drawback is the same as the wet layup, the part could be heavier than needed.
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This is the current manufacturing technique for MSXIV. Prepreg contains resin in a solid-state that becomes liquid and slowly cures at room temperature. However, room temperature cures over the span of a few weeks. Instead, higher temperatures are used (70+ Celsius) in order to turn the resin into liquid more easily.
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Video of prepreg layup: https://youtu.be/HfrFaKDsJxc
Carbon Fiber Layers
Before I hop into this topic, a few concepts need to be understood 😃
Tension and Compression in Bending
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When a beam or part is put in bending, there will be tension (material below the green plane), compression, and a neutral axis (green plane). In our case, we’re really only concerned with tension forces. This is because failure in a carbon fiber part is when the fibers exceed their tensile strength and begin to snap/fray.
Isotropic vs. Anisotropic materials
Isotropic materials are defined as one that is equal in strength in all axes. This means that if I were to grab a blank sheet or block of raw material, I could machine my part in any orientation and the strength would be the same.
Anisotropic materials are materials that are stronger in one axes vs another! A common example is wood - it's much stronger if you push it downwards and allow the fibers to bend.
Here’s a good video for a more in-depth explanation: https://youtu.be/Hu4zjPIeDq8
Applications in Carbon Fiber
In the majority of carbon fiber parts, we want the panel to be isotropic. This is cause the load cases are not always fully defined. For example, the floor panels of the car, we cannot guarantee that the passenger will step on the exact same spot every time. Therefore, we need to ensure our panels are able to sustain loads wherever they COULD be applied.
To do this, we leverage the fact that carbon fiber strands are really strong in tension! We orient the fibers such that when the part is bent, the fabric is put into tension as opposed to the epoxy.
Here’s a quick visual
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In this first picture, the fibers run towards the load/force. In this case, when the load is applied, the part bends and puts the fibers in tension. Since carbon strands are strong in tension, this part would be very good at sustaining loads similar to the one shown.
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In this second picture, however, the strands of carbon are running perpendicular to the load. In this case, when the part is loaded, the epoxy is put in tension as none of the fabrics run in the correct direction to sustain the tensile forces. This means that the part would snap much earlier 😞
For those that are keen, you may have noticed that the first case could easily turn into the second scenario if you were to relocate the load such that the fiber directions run away from the load. This is why we stack up multiple layers of carbon fiber with strands running in multiple different directions!
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0/90
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45
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others used
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By having strands of carbon running in multiple directions, we ensure that when a part is bent from an arbitrary location, the strands are able to sustain the tensile loads!
Common Fiber Arrangement
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Shown above are the 2 most common fabric arrangements. At Midnight Sun, we do 6 layers instead of 5 so that “stack up” looks a bit different. However, the concepts still hold.
0/90 ply infers that the strands of fabric run length and widthwise on the part. -45/45 infers that the strands run 45 degrees offset from length and width. 45-degree layers allow a part to be more versatile for all load cases but less specialized for a particular load case.
A 0/90 layup is the colloquial term for a layup containing only 0/90 layers and a quasi-isotropic layup is a term used to describe the picture on the right. It’s called quasi-isotropic as it is only part isotropic.
Below is a picture showing differences in deflection of 2 parts, both under the same load. One being a 0/90 layup and one being quasi-isotropic.
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As you can see, the 0/90 layup deflects far more as there are no fabrics in the direction necessary to sustain the load. This leads to the 0/90 fabrics only being able to contribute a “component” of strength, similar to vector addition.
This world of fabric orientation customization can be used anywhere, you can add strength to a part in a very specific direction!! So long as you have a defined load case, you can optimize your part, structurally, to handle that load!