pushrod strength test - alum vs steel

Jim,

I don't think Ultimate Strength of the material is the governing factor in this instance. I believe it is the Modulus of Elasticity. Take a look at Euler's Column equation on Wiki.

I venture to say there's not that big of a difference in Modulus of Elasticity between 6061-T6 and 2024-T3.

The above is consistent with Snotzo's statement:

Snotzo said:

I repeat what I said earlier, the difference in use as pushrod tube between 6061 and 2024 is negligible for all practical purposes.

Click to expand...

Ultimate tensile strength relates to testing a sample to failure in tension, i.e., pulling on it until it fails. In contrast a pushrod is used in compression, and the modulus of elasticity, not the tensile strength, describes the material’s stiffness, i.e., its resistance to deform. The link below provides modulus of elasticity for a variety of aluminum alloys and steel alloys. Note that all the aluminum alloys are around 70 GPa whereas the steel alloys are all greater than 200 GPa, or restated, the modulus of elasticity for steel alloys is ~ 3X that of aluminum alloys. And of course this is why the steel pushrod can be a much thinner material than the aluminum one.

http://www.amesweb.info/Materials/Modulus-of-Elasticity-Metals.aspx

WZ507 and Dances – According to the modulus of elasticity, 2024 is stronger than steel. Steel tubing is 2.95 times as heavy as identically dimensioned alum. 2024 has a modulus elasticity of 72.4 Multplied times 2.95 = 213+ and that beats all the steel alloys shown on the chart (referred to by the above post) with their modulus elasticity of 207

Dances. Your are right – its 25% difference but I was multiplying by 125%... Does the above show that alum has less spring/flex than steel per weight?

WZ507 - I used tensile strength because it was readily available. 2024 alum has approx twice the tensile strength per weight as 4130

Anyone can take a thin rod of 6061 and 2024 alum and simply bend them in his hands. There’s no mistaking the superior bending resistance of 2024, I dare someone else to make this easy test. It would save a lot of time and verbage.

jseng1 said:

WZ507 and Dances – According to the modulus of elasticity, 2024 is stronger than steel. Steel tubing is 2.95 times as heavy as identically dimensioned alum. 2024 has a modulus elasticity of 72.4 Multplied times 2.95 = 213+ and that beats all the steel alloys shown on the chart (referred to by the above post) with their modulus elasticity of 207

Click to expand...

Here's a nice comparative table of 2024-T4 to 4130 Chromoly

http://www.makeitfrom.com/compare/2024- ... -Mo-Steel/

I am getting a density ratio of 7.8/3.0 = 2.6......not 2.95 as you listed above. How did you arrive at 2.95? Using your analysis above, 2.6 X 72.4 = 188.2; not 213 as you listed above.

So with your analysis 188.2 < 207, with steel being about 10% greater.

.

Dances with Shrapnel said:

jseng1 said:

WZ507 and Dances – According to the modulus of elasticity, 2024 is stronger than steel. Steel tubing is 2.95 times as heavy as identically dimensioned alum. 2024 has a modulus elasticity of 72.4 Multplied times 2.95 = 213+ and that beats all the steel alloys shown on the chart (referred to by the above post) with their modulus elasticity of 207

Click to expand...

Here's a nice comparative table of 2024-T4 to 4130 Chromoly

http://www.makeitfrom.com/compare/2024- ... -Mo-Steel/

I am getting a density ratio of 7.8/3.0 = 2.6......not 2.95 as you listed above. How did you arrive at 2.95? Using your analysis above, 2.6 X 72.4 = 188.2; not 213 as you listed above.

So with your analysis 188.2 < 207, with steel being about 10% greater.

.

Click to expand...

I was comparing the actual weight of the tubing.

3/8" OD steel with .065" wall is .218 lbs per foot.
shown here:
http://www.onlinemetals.com/merchant.cf ... op_cat=197

3/8" OD Alum with .065" wall is .0744 lbs per foot.
shown here:
http://www.onlinemetals.com/merchant.cf ... top_cat=60

.218 divided by .0744 = 2.93 (above I divided .218 by .074 instead of .0744).

I rounded off but 2024 alum still comes out stronger at 212 modulus elasticity (instead of 213).

Regardless of who's numbers they are - they need to be checked against empirical evidence. The hydraulic jack test at the beginning of this thread as all we have so far.

Steve Maneys pushrods is said to be 0,040 in wall thickness and he claims them to be lighter than std ? Makes me think, the weight of solid ballends must have a great part of the total pushrod weight.
So, making the ballends short and light must be as important as a thin and light tube.
A concern about the thinwall tube mentioned here, they might be too weak to keep the pressfit to the ballend?(0,018 as suggested here)
A middle of the road maybe, like 0,025 ? or even like Ken Canagas 0,035?

Sten

billet
the point you make is acknowledged, and can make a great difference to a fully assembled pushrod, but the discussion here is focussed on the compressive strength comparison between a steel and an aluminium pushrod tube, i.e tube only less ends.

js
If you are not inclined to make your own calculations using the Euler column formula, then the only way forward is to avail yourself of a materials tester, either beg, borrow or buy, and conduct tests in accordance with the appropriate guide lines for a column. As an alternative to making your own calculations, you may rely on mine made using Prof. Blair's software, which have as a base the equations developed by Euler.

If you want to cover both possibilities and can make your own Euler calculations AND have the results of compressive tests for comparison, you will still find that steel is the superior material - as I and others have indicated in previous posts.

What Snotzo said.

Jim,

Your analysis is incomplete and misleading in the context of pushrod material; especially within the constraints that a Norton big twin poses. If you have looked at the Euler Column formula you would have seen that both the Modulus and Minimum Area Moment of Inertia are in the numerator so with an equivalent weight Aluminum pushrod you have dramatically changed the Minimum Area of Inertia.

Snotzo
It would be nice to find some better testing equip. I would rather do that than get into the math.

Dances & Snotzo
If I sent you a sample of 3/8" dia 2024 and 6061 alum and 4130 steel) - would you perform a simple bending test and report what you experience?

Jim

Snozo
Yes, I understand that the topic is about compression strength alu-steel tube.
I find it very interesting even as an amateur compared to you.
But we also compare the weight in order to get down to the same totalweight with steel as alu and still get advantage of compression strength, dont we?
If i got it right, 0,058 alu tube/0,018 steel tube have the same weight but the steel tube have higher compression strength?
Interesting but if the thin wall is too weak to keep the ball end in place which was my concern must be relevant even in this topic?
I will be happy to be enligthened

Sten

Hi Jim,

If I may, If you put out a call to the racers on this forum you would probably find enough junk Commando motors to put together the necessary parts to run a couple sets of push rods and see what happens. JimC seems to have worked out how to spin a test mule at high rpm. I bet he would tell you how to do it. I don't think I would stand right next to such a contraption but...

Greg

JS

you started with a test to try and determine the compressive strength of two tubes typically as used in the manufacture of an engine pushrod.
I gave you answers for A/ tubes of identical size, i.e length and outside diameter, and identical wall thickness, and B/ the same tubes having the same length and outside diameter, but with a changed wall thickness to give identical weights. These were the results of calculations made to determine the maximum buckle strength. Now you want to introduce a bending test by hand, which, however it is done, cannot in any way, shape or form, be comparable to a buckle test.

There is a possibility that somewhere in your area a company has a material tester. An enquiry of a tester manufacturer may give you the contact details of where such testers have been sold. The Lloyd material tester in the Queens University, Belfast is regularly in use by the students working on different projects, otherwise I would see if they would conduct the tests there.

When you can show me an engine that will bend a pushrod tube in the manner you describe, I'll show you an engine that is totally screwed up!
They do bend in use it's true, but the bending is a result of loads applied at the ends, i.e a compressive force.

Billet
I don't intend to add pushrod ends of any kind into this discussion, my focus is solely on the buckle strength of the tubing. Once that issue has been resolved, THEN I am prepared to include the end fittings in any discussion that may follow on.

Snotzo & Dances

I made some inquiries and the Lloyds material tester costs about $100,000
Having an engineering firm test the tubes for me costs about $800
Finding someone to do it for nothing may be impossible or would at least require a lot of time.

So I'm stuck in a situation between math and empirical testing that has not found agreement. For me the toggle bar test is fine because I'm only comparing the two - not looking for numbers. It just needs careful alignment with ball bearings in the center and on the ends of the tubes.

Using tools and data that was readily available to me I tried my best to be objective without spending a fortune. It got interesting and went way deeper than I expected. If someone wants to prove it one way or another with some expensive equipt - I'd like to see the results. Best option is finding someone at a friendly University engineering dept.