Inflate aluminium tube to increase it’s strength?

In summary, the conversation discusses the structural properties of a thin walled aluminium tube and the potential effects of pressurizing it with compressed air. It is suggested to also consider the tension on the tube's wall and to increase the thickness of the walls to prevent potential rupture. Other methods such as pre-stressing styrene foam and using multiple lines to tie the wing spars together are also being explored in order to reduce weight.
  • #1
swerdna
251
0
I’m designing and hope to build a human powered helicopter (HPH) and am wondering if pressurising a thin walled aluminium tube by filling it with compressed air would strengthen it’s structural properties.

Hope this is the right place to post this.
 
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  • #2
Good luck with the HPH. Here's a place to start when considering pressure.

e.g. consider the tension on the tubing's wall.

lapb.jpg
 
  • #3
dlgoff said:
Good luck with the HPH. Here's a place to start when considering pressure.

e.g. consider the tension on the tubing's wall.

lapb.jpg

Thanks.
 
  • #4
Also, it will depend on the loading on the beam. Pressurizing the thin walled tube induces axial and hoop stresses. Thus you increase it's compression strength in the axial direction, but be very careful that the hoop stresses are not increased so much that you exceed the yield strength causing rupture.

From a stress analysis and fracture mechanics perspective, I would be much more inclined to increase the thickness of the tube walls, even if it increases the weight. Ideally, you can fit several thin tubes inside each other, in order to prevent brittle fracture (which would be veeery bad for you application)
 
  • #5
Thanks. I agree that pressurising aluminium tubes probably isn’t the best method. I’m working on other methods that include pre-stressing styrene foam, cable-staying and creating an inverted conical shape with the wing spars and tying them together with multiple lines like a spider‘s web. Overall I’m trying to reduce the weight of the wing spars I use.
 

FAQ: Inflate aluminium tube to increase it’s strength?

1. How does inflating an aluminium tube increase its strength?

When an aluminium tube is inflated, the internal pressure increases, causing the material to expand and become more rigid. This increase in pressure also creates a compressive stress on the walls of the tube, making it stronger and less likely to bend or collapse under external forces.

2. Is there a limit to how much an aluminium tube can be inflated?

Yes, there is a limit to how much an aluminium tube can be inflated. If the internal pressure exceeds the yield strength of the material, it will permanently deform or even rupture. It is important to carefully monitor and control the pressure during the inflation process to avoid damaging the tube.

3. What is the benefit of using an inflated aluminium tube over a solid one?

The main benefit of using an inflated aluminium tube is that it can be made stronger without adding any additional material. This makes it a lightweight and cost-effective option for applications where strength is a crucial factor, such as in aerospace or automotive industries.

4. Can inflating an aluminium tube make it more resistant to corrosion?

While inflating an aluminium tube can increase its strength, it does not have a significant impact on its corrosion resistance. The best way to prevent corrosion in aluminium is by using protective coatings or alloys specifically designed for this purpose.

5. Are there any risks associated with inflating an aluminium tube?

There are some risks associated with inflating an aluminium tube, such as over-inflating which can lead to deformation or rupture. It is important to have a thorough understanding of the material and proper equipment to carefully control the inflation process and minimize these risks.

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