Steel for Olympic Barbell

Hmmm. I'm rusty on a lot of this (no pun intended ). "Brittleness" is not a term that metallurgists ordinarily use. They look at elongation, and the gap between yield strength and ultimate tensile strength. Charpy and Izod impact strength are additional terms. In discussions of tool steels, you'll also see the term "timbre," which is not well-defined.

What you're looking for, I think, is a determination of what happens when the yield strength of the bar is exceeded. Does it bend, or does it quickly reach the ultimate tensile strength, and snap? And if it bends, how much does it bend before it snaps?

Right? If that's the case, I don't know the answer. I know that 5% elongation suggests little bending before it snaps. As for thin versus thick, that's a problem of mechanics: a 5% elongation in tension allows more bending, in terms of degrees of bend, in a small wire versus a thicker bar. So a smaller bar should bend more before breaking than a larger one, all other properties being equal. This is discussed in terms of the behavior of the "outermost fibers" (theoretical) of a beam, including a wire or bar. It also explains why a 300 kpsi piece of music wire will bend quite a lot before breaking.

I think. Maybe someone who's more up to date on Statics and the Strength of Materials (that's the title of a good book on the subject) can chime in and correct me on this.

Be sure to watch the movie clip in the picture choices. Nice drop tests that passed.

Martin

I would think that 4130 would be a better choice than 4340.

Dan

The video is interesting, but I was more impressed with the bending test done in a machine. It's hard to tell what the actual load is on the bar in those drop tests.

The actual load in the drop tests is easy to tell. Each plate is 45 lbs.

Yes but tempering takes away hardness(brittleness also)as well as strength. Strength and brittleness have a strong correlation.

Dan,

4130 doesn't meet my strength requirements. Remember, I need the bar to res ist permanent deformation. That can be achieved only by high yield strength . The standard is 200000 psi Tensile strength with ~ 180000 psi yield stren gth. Even then bars bend with abuse.

But that doesn't tell you what the load is on the bar, as a result of being dropped with the weights on it.

For example, dropping it straight down and with the bar horizontal imposes very little load on the bar.

Dropping it on a 45-degree angle to horizontal imposes a higher, but unknown load. Note that the bar doesn't bend much in that test. The load is not really very high, although it is more of an impact load.

Yes, it's a balancing act of magic, metallurgically speaking.

The above page gives approximate formulae to calculate impact stresses.

Yes. What I would love to know is though, what is the elongation % and reduction in area of the bars at the given strength. Something no manufacturer is willing to tell.

I really don't think that would answer it for you. When a bar is held at 45 deg. to horizontal and dropped, the impact of the lower weights is not transferred to the bar. It's absorbed by whatever is on the ground.

The impact imposed by the upper weights depends on a complex set of forces and deflections, which involve tracing the forces from the upper weights, through the bar, to the lower weights, to where the lower weights contact the ground.

Good luck with that.

A failed, discarded bar might.

If you plan to make these things you need a way to proof test them anyway.

See Bethlehem Steel's "Modern Steels and Their Properties." This is a scan minus the attribution:

Excellent! I see 202 pages of unexpected reading in my near future. Link saved.

True, what you say, which is why I wrote approximate.

And therein lies the problem. The driving force behind me wanting to make a bar in the first place is a complete lack of quality equipment in my country. Elite athletes all import Eleikos. However they are sponsored. I am not.

If you really want an engineering analysis of the loads and deflections, this is a job for finite-element analysis (FEA). The tools for doing that today are amazingly good. It would make a good term paper for a mechanical engineering student.

However, what you have when you're done is a theoretical set of behaviors based on nominal mechanical properties of the bar. You then need to apply a safety factor, and that wouldn't be a piece of cake for this job, either.

I don't know why you're making your own, but if I were doing it, I would copy the material and dimensions of a commercial bar that is known to be safe and successful. "Chrome-moly" is going to be 4340; I would bet on it. But you could confirm it by asking the bar manufacturer. I do that kind of thing all the time, as a writer in the field. Most are forthcoming if it isn't about some proprietary issue, and I can't imagine that this one is. They've publicly stated the class of alloy; all you need to know is the last two numbers, which is the carbon content. Again, that number is almost certainly 40.

Good luck with your project.

Thanks.