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Replacement material for 35 mm OD Dural tubing AU4G/2017a

Replacement material for 35 mm OD Dural tubing AU4G/2017a

Replacement material for 35 mm OD Dural tubing AU4G/2017a


I have an issue with trying to find a replacement for 35 x 31, 35 x 25, and 30 x 26 mm DURAL tubing.

I am working with this design: http://home.caiway.nl/~fnijhuis/zekitez/buggy/sb_b...

If you look at the way the Down tube (tube AU4G 35x31 L=500 mm)attaches to the Central frame tube (tube AU4G 35x25 L=420 mm) you can see that an enormous torque is applied to the Central frame tube. Most aluminum materials at these thicknesses would be torn apart. The joint between these two is drilled and pinned with a bolt unlike the normal clamping used to attach Kee Klamps and most of the rest of this buggy. I would doubt that this design could even work if it were not for the pictures of this device in action and the builders assurance that he has put 800 bumpy Kms on this buggy with no issues. In addition the builder reports that at one point he installed a longer axle (20% 1000mm changed to 1200mm) and that the longer axle bent where the 1000mm axle worked fine. This tells me that this design is right at the edge using Dural and therefore is probably as light as it can be using that material.

Dural is an obsolete trade name for the earliest aluminum and copper alloys used in aerospace. The name continued to be used in France but as a result of various evolutions of the designations and standards, it was then called AU4G (Standard NF A 02-104), and then 2017 (Standard NF A02-004 / EN 573-1) and now finally 2017a.

2017a T3 is as far as I can tell a very close match for the properties of "Dural" but 2017a is NOT commonly available in tube form. So despite having found the correct modern replacement material I STILL have to find an alternative that is actually available for purchase as tubes with OD anywhere from 33 to 35 mm. (to fit the Kee Klamps).

6061 T6 has far lower tensile strength(310 MPa)than dural (420-500 MPa) and I can not find 33 to 35 mm 6061 T6 tubing that would have sufficient wall thickness to make it work in this application. Not even close. I have not bothered to look for 35 mm RODS of any Alu material as I believe this would be far too heavy and expensive even if available.

Locally available 1.375 OD x 0.049 WALL x 1.277 ID Seamless Stainless Steel 316 Round Tube Would certainly be strong enough but it's Weight/Lineal Foot is 0.909 pounds! Perhaps I could find thinner stainless (again at 1.375' or 35 mm OD) but would it be strong enough? How thin can I go with these highly strained parts?

I even considered trying Carbon fiber tubes. This page:


compares and contrasts "aluminum" with a reported Ultimate strength of 500 kN · m/kg with CF (and steel) and makes the following cavalier statement "A component made from standard carbon fiber of the same thickness as an aluminium one will offer 31% more rigidity than the aluminium one and at the same time weigh 50% less and have 60% more strength."

This strikes me as useless gibberish designed to sell product with no relation to reality at all. Am I wrong? If I take this information at face value I should be able to bolt together 35x31 CF tubing and end up with a vastly stronger and more resilient frame but I suspect even using 35x25 (5mm thick!) CF tubing would result in an explosive shattering of the material on the first big bump. Do you agree? CF is known to degrade over time and without any indications it can become weaker and weaker over time anyway.

I am beginning to think this design CAN NOT BE BUILT TODAY using any commonly available tubing. At least not using all the same material. The only viable option I have been able to come up with so far is to use 1.375 OD x 0.049 WALL x 1.277 ID Seamless Stainless Steel 316 for the Downtube, Central frame tube, axle and forks and try using 1.375 X 0.058 seamless 6061 T6 for the lesser stressed members in order to reduce the overall weight.

If you were to try to replicate this design what (commonly available) 33 to 35 mm tubing would YOU use?

Thank you in advance for any guidance you can provide.


RE: Replacement material for 35 mm OD Dural tubing AU4G/2017a

Flyboy , You might do well to look at 2024 aluminium tubing, this is available in T3 and T36 tempers.
2017- T4 has a yield strength of 40,000PSI, 2024 -T3 has a yield strength of 50,000PSI . this compares to 6061 T6 which yields at 37,000PSI .

You are judged not by what you know, but by what you can do.

RE: Replacement material for 35 mm OD Dural tubing AU4G/2017a

Thank you for the quick answer. I have been looking around for days, posted to two forums and you are the first person who has actually given me any good information whatsoever. At first look yes this may just be what I am looking for. 2017a is definitely supposed to be the correct "replacement" for Dural but since nobody makes tubing out of it another material will have to be selected.

To contrast and compare:

Matweb reports 63800 psi Tensile Strength, Ultimate this converts to 440 MPa and Dural is reported to be 420-500 MPa so 2024 -T3 appears to be in the ballpark at least. It's on the lower end of the strength range of Dural however. (who knows what the original builder really had? All he said was "Dural"). was it 500 or just 420 Mpa?

During my analysis I worked out a design change that would greatly reduce the stress of the downtube/central frame tube assembly allowing for other materials to be used in place of Dural. I believe a combination of Steel for the axle (allowing for a greater than 1m axle length) 2024 -T3 for the highly stressed front end and good ol' 6061 T6 for the lesser stressed parts (to save cost) may be my answer.

Anybody else who would care to weigh in will be appreciated. In the meantime I will asses the viability of 2024 -T3 further.


RE: Replacement material for 35 mm OD Dural tubing AU4G/2017a

Oh Ho! makeitfrom.com/material-properties/2024-T3-Aluminum says it is 480 MPa ultimate and 320 MPa yield! The range of tensile strength for Dural is not very explicit (420-500 MPa) I do not know if that is a range for ultimate strength of various tempers or if it is meant to show the Yield at 420 and the ultimate at 500. I would GUESS it is the rage of ultimate strengths for various Dural tempers/formulations.

If this is correct (range of ultimates) then 2024-T3 appears to be appropriate for any part of the buggy unless you wanted to extend the Axle in which case a single stainless tube at a pound a foot could be substituted. With my stress reducing design change I believe I have my answer.

Anyone know for sure? (actual parameters for this old Dural material)?

RE: Replacement material for 35 mm OD Dural tubing AU4G/2017a

I have another Oh Ho! matweb says "General 2024 characteristics and uses (from Alcoa): Good machinability and surface finish capabilities. A high strength material of adequate workability. Has largely superseded 2017 for structural applications."

So despite 2017 being the official replacement for Dural it has since been "superseded by 2024! for structural applications" is not available in tubing while 2024 is!

I have found it to be available in a wide enough range of wall thicknesses that I think I should be able to source what I need.

I believe I have my material.

RE: Replacement material for 35 mm OD Dural tubing AU4G/2017a

So you are all set then.

You are judged not by what you know, but by what you can do.

RE: Replacement material for 35 mm OD Dural tubing AU4G/2017a

I want to thank you again for your assistance. I have confirmed that all important properties are similar and that this material is the ACCEPTED material to use in place of 2017 (Dural) if you need to use tubing.

I had posted at another professional engineering forum and got answers to all kinds of questions that I did not ask and not even ONE material suggestion. Complete waste of time and effort to even ASK.


RE: Replacement material for 35 mm OD Dural tubing AU4G/2017a


2024 Tubing

6061 Tubing

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

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