Material calculator/equation??

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Material calculator/equation??

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speed_demon	speed_demon posted 10 Years Ago HOT Topic Details
Group: Forum Members Posts: 23, Visits: 163	Hello, I have been reading everything I can find about composites but I haven't found any type of equation/calculator for determining composite thickness requirements. I know different resins, etc. have a bearing on the strength but, there's got to be a "safe" relation between how much composite equals the strength of an object made of steel/aluminum. I am trying not to waste too much material and loose the weight saving of making parts out of composites. I'm also not looking to make parts that risk my life on (bike frames, control arms), just automotive body panels, intake manifold or a pickup tonneau cover. I think a formula wouldn't be too hard that would make parts safely 15-20% strong than OEM and still have a substantial weight savings. For example: How thick would a fender need to be if it was made out of e-glass or carbon fiber vs. OEM sheet metal? I know a wheel well would have to thicker to survive a rock from the tire tread at speed, but how thick? Would a layer or two of kevlar add to 2mm of e-glass be good or over-kill? Everywhere I see PSI tensile strength,etc. but does it mean that I would need half the thickness of an aluminum bracket if the fiberglass is twice the metal's strength rating? Thank you for your time, hope to hear back from you soon.
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Chris Scott	Chris Scott posted 10 Years Ago HOT Post Details
Group: Forum Members Posts: 20, Visits: 235	The reason why this is an impossible comparison is that even within the 'carbon fiber' family, there is no conversion. Take a simple three point flexural test... for every different possible way you can manufacture a CFRP beam, you will get different results. Also, while you might find that a beam made of uni-directional construction with 0 angle (longitudinal) might produce impressive results on a three point flexural test, but when you start adding in torsional forces(torque) it won't perform as well. Simply by changing the angle of the tows you will develop completely different characteristics. Most metals are incredibly isotropic materials, so you gain strength in all directions automatically. With CFRP you have to design your own properties. Think of CFRP as offering infinite customization! I could probably just type for pages on this subject, but instead I'll offer some tips and considerations to make when designing your parts and be helpful! :] - Vacuum bagging/infusion will significantly remove/reduce voids in your product. Be mindful of resin content % as well. Voids/dry spots will significantly reduce your stiffness while excess resin will brittle your part. Also using vacuum will help in producing consistent product. - Composites gain their strength with geometry. One of the ways to improve geometric strength is by adding a lightweight core. Also stay away from sharp corners. - Orientate your fabric weaves appropriately. - Remember you can add partial layers to areas of concern, - Not all tows and not all fabrics are made equal...also not all resin are equal too. I've spent my fair share of time and money wasting it on cheap stuff and trying to cut corners, not worth it. - Anything exposed to the sun, recommend protecting it with a good automotive clear or a specific gel coat that will help protect your product from UV rays which will yellow and embrittle the resin. This is not a concern for steel components. I hope this helps. Use test pieces to practice any new processes, or if you are unsure of the result. Worst case scenario, you manufacture a part that does not have the required stiffness/strength you desire, you can easily just scuff up the back side of the part and continue to lay more materials until you are satisfied. Also allow your parts to post cure, you'll find that resins will reach full strength over time.
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