Strength of PLA

[YuriS]

Hi,

I am looking for an advice for designing a propeller blade that I will use for my science project.

I am studying the twist angle of blades and have already designed and printed a prototype.(attached image)

As I continued with my research I have realized that analyzing the force produced by the blade will be easier with flat surfaces, so I have decided that I am going to make the cross section of the blades rectangular (and not elliptical like in the prototype).

My question is, how thick should I make the blades?

I need it to be as thin as possible so it does not weigh too much so it can be rotated by a motor, however I do not want it to be too thin and bend as it rotates either.

I am thinking of a range of maybe 1.6 mm to 6.0 mm…

Thanks!

[MB3D]

Hi there! You should go for roughly 3mm and then change upon your research results. A very important fact, that you have to concider is how to print this piece. If you print the layers along the direction of the blade, you should get stronger parts. Do you print this yourself or do you get this made at a hub? If you need a hub to make this, I would like to help you out! Contact me via my hub : www.3dhubs.com/siegen/hubs/marius You should concider to make this in other materials, like Colorfabb xt, Taulman T-Glase or Taulman Nylon. Another extraordinarily strong material is Taulman 910 alloy 910 which I have in stock tomorrow. PLA is brittle and will break instead of bend. If you want a quick sample print of those materials I’d like to help you out with that. Please contact me via my hub, if you do stress testing with those materials above I’d give you a discount when I get the results, I’m interested to know, how durable those materials are etc. These other materials should be strong enough, even at a thickness of 1,5-2,5mm. Hope to hear from you, Marius Breuer

[rpelissier]

Hello,

To my (little) experience, 3mm thickness is the minimum for PLA to be rigid enough over 5-10cm length.

My advice: print a set of 3 bars: 3*3*100, 5*5*100, 8*8*100. It will cost you only a few dollars and you will be able to decide by yourself what suits your needs. Are you in Paris? I live there too.

[3DAmsterdam]

Hello Yuri

This is a very complicated question you ask. The strength and the performance of a product is depending on very much factors. Resp:

The material, how it is printed (temp, speed ect.), the temperature of the environment, how much sunlight it gets, the age of the material, the expected lifetime, the forces and the character of these forces (repetitions, static, incidental peaks) and the risks when it fails. All together it is always a compromise.

The best way to start is to make some of these propellers you had in mind and test it til it fails (in a save way). Study when en how is breaks. Some failures you get at the start others after a period of time. Improve it till it is good enough to have an acceptable reliability and lifetime. Specify how it has to be used and how not. Test it on a bigger scale and do the same, note your failure.

Sometimes a small change in the product for instance the color can make a big difference in the performance. So choose your suppliers and materials so that you don’t have to do this every year.

Have fun with your project.

Greetings Bert

[Martin20118]

Hi Yuri,

Seems like an interesting project you are doing. I am a student in Aeronautics and from my experience you don’t necessarily have to make the blades thinner in order to make them lighter. You could also make internal hollow structures to make your blade stiffer while keeping it light. If you want I could help you out with this, just let me know!

Good luck!

[YuriS]

Hi,

Thank you! It is my dream to study Aeronautics at university!

I will consider hollow structure as well.

Thanks,

Yuri

[YuriS]

Hey!
Thank you! I will consider making three bars and see the actual object for myself.

[YuriS]

Hi!

Thank you! I will start my next propeller with 3mm, and see if it would be durable. Also I will see for other alternate materials, however I think I would keep PLA as my budget is limited. Thanks again for your advices!

[YuriS]

Hello!

Thank you very much for your advices. I am thinking of printing few test types soon, so I will also see the durability myself.

[MB3D]

The other materials are just as cheap or a little bit more expensive. I offer Colorfabb XT for 0.60€/cm³, which is less then other hubs charge for PLA. Also think of the following: Either you get a 4,5mm thick part out of PLA, the part maybe has to be that thick, to be durable enough, or you get a 1,5mm thick blade out of XT or similar materials, which gives you the same strength. In the end you might save cost and weight if you go with the right material.

Especially the way you printed the blade in the picture makes me think, that the blade will break easily along the layers.

All 3d printing parts are stronger in the same layer and if they break they’ll most likely do between two layers.

If there’s no way to orientate the models differently, I would recommend Taulman3d materials. The brand “Taulman3d” produces materials, that have astonishing layer-to-layer bonding strength. As best you’d choose Alloy 910, even though it’s more expensive then Nylon, it doesn’t soak up water. Nylon can take up to 25% of it’s own weight in water, which results in a big loss of strength.

You might want to contact me, to get more material recommendations. Also if your final choise is PLA I would recommend to go with PLA/PHA by Colorfabb instead of normal PLA.

PLA/PHA is not as brittle and will bend a tiny bit, when PLA would already break.

Cheers,

Marius