Materials Science of the Barbell | Andrew Lewis

[stef]

"[T]o be clear, most reputable barbell manufacturers sell barbells that are fine for training. Just buy a well-reviewed, general purpose 20kg bar from Texas Power Bars or Rogue Fitness, and you'll probably be happy and never even wonder why. However, if you want to actually buy and use barbells and plates intelligently, you will need to understand some metallurgy and physics."

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[Nockian]

Interesting, particularly the DL info. I use a thin bar to DL and one of the lads was watching the lifts. He said that it looked like the bending of the bar was throwing off my form by causing a slight loss of tightness. He suggested I pulled out the slack prior to moving shins to the bar.

I’m going to ask a stupid question. I can already imagine Rip doing a face palm ��‍♂️

If we get perfectly set up for the pull and the bar bends an inch or so, is that compromising the set up by effectively moving the hips lower than ideal ?

[rero360]

As a mechanical engineering major, I enjoyed this article. I do have one question however, at the end it states to not deadlift with all rubber plates. Why is this? When I built my home gym I went with bumper plates in an effort to minimize noise as the gym is outside, directly below my little boy's room and I workout after he goes to bed. Now granted he currently doesn't sleep in his own room (only 2) and I've recently learned that bumpers are not really any quieter, but I do hope to get him in his own room soon.

Off the top of my head, I'm thinking the reason to avoid bumpers is that because they have a greater thickness, you end up with weight further out on the sleeves, thereby increasing the lever arm between your hands and the weight, thus increasing deflection in the bar. Is this it?

[JJ23]

Interesting article. I've never seen yield strength specified on a bar, only tensile strength. Assuming they're relatively correlated (maybe not a safe assumption), I think the formula provided is useful for putting a thinner bar with higher tensile strength on an apples to apples basis with a thicker bar with lower tensile strength.

[Sam Beckham]

...

Off the top of my head, I'm thinking the reason to avoid bumpers is that because they have a greater thickness, you end up with weight further out on the sleeves, thereby increasing the lever arm between your hands and the weight, thus increasing deflection in the bar. Is this it?

I'm pretty sure that's the idea there. If you are used to training with bumpers and were to switch to iron (like a competition or something), you might overestimate your lift. I don't think it matters at all to most of us as long as we are using the same plates and progressing.

I liked the article. I've tried explaining the modulus/diameter are what determine flex but I think most people are firmly convinced that the advertised tensile strength plays into it. I do remember having a hard time swallowing that the modulus doesn't change with heat treat back when I took mechanics of materials.

[TommyGun]

Well done Andrew. I am tempted to bust out my old mechanics and strength of materials books.
We have waited for the barbell deformation article and you did it.

[Satch12879]

Interesting article. I've never seen yield strength specified on a bar, only tensile strength. Assuming they're relatively correlated (maybe not a safe assumption), I think the formula provided is useful for putting a thinner bar with higher tensile strength on an apples to apples basis with a thicker bar with lower tensile strength.

This is very deep in undergraduate mechanics of materials, but for steel, the correlation between yield strength, or where the material begins to deform, and ultimate tensile strength, where fracture occurs and thus loss of load-bearing capacity, is not clear or not clearly related in a linear or remotely linear way.

At the end of the day, the distinction is not really useful. What you're concerned with is the deflection of the bar under load. The variables that affect deflection are the cross section of the bar, the modulus of elasticity, and how the bar is loaded. A thicker circular bar will deflect less than a thinner circular bar, regardless of the tensile strength.

Great article, Andrew. I'd nitpick about the stress/strain diagram not being correct for steel, but it's a minor point.

[AndrewLewis]

If we get perfectly set up for the pull and the bar bends an inch or so, is that compromising the set up by effectively moving the hips lower than ideal ?

No it's not, because you'll just be one inch into an ideal deadlift if you set up correctly. If your gym friend noticed you were losing tightness as you pull the bend out of the bar, it seems likely you're not setting up tight enough. You also might be "jerking" the bar off the floor by accident.

Off the top of my head, I'm thinking the reason to avoid bumpers is that because they have a greater thickness, you end up with weight further out on the sleeves, thereby increasing the lever arm between your hands and the weight, thus increasing deflection in the bar. Is this it?

You got it right. The center of mass of each side of plates moves further apart. Instead of a length of 58" with cast iron, you might an effective length of 65".

Interesting article. I've never seen yield strength specified on a bar, only tensile strength. Assuming they're relatively correlated (maybe not a safe assumption), I think the formula provided is useful for putting a thinner bar with higher tensile strength on an apples to apples basis with a thicker bar with lower tensile strength.

As I mentioned in the article, the tensile strength is of no use to determining the strength of the bar for our purposes. The yield strength is more helpful. The yield strength and tensile strength are correlated, but with such a wide range that it is not helpful. For example, you could have one steel with tensile strength of 220ksi and a yield strength of 70ksi and another steel with the same 220ksi tensile strength, but a yield strength of 200ksi.

[Mark Rippetoe]

Off the top of my head, I'm thinking the reason to avoid bumpers is that because they have a greater thickness, you end up with weight further out on the sleeves, thereby increasing the lever arm between your hands and the weight, thus increasing deflection in the bar. Is this it?

Did you not read the article?

[AndrewLewis]

Well done Andrew. I am tempted to bust out my old mechanics and strength of materials books.
We have waited for the barbell deformation article and you did it.

Thank you. I'm glad you liked it.

Great article, Andrew. I'd nitpick about the stress/strain diagram not being correct for steel, but it's a minor point.

Thank you for the compliment.

The stress-strain curve is from a real tensile sample of steel, so I'm curious what about it makes you believe it's not correct for steel.