steel strength

[petar yovchev]

Hi guys
Is it possible a steel to withstand 1600MPa in bending, because i'm a witness of that by applying 260Nm (90kg x 0.3m)bending moment of a shaft Ø12,
It withstood it even without crook.
According to the formula σ = (32.M)/(π.D^3) = 1532MPa
Is that true or I'm wrong in the calculation.
Thanks in advance for your opinion

 

[EdStainless]

Check your units, yes the equation is correct if both ends are free.
If one end is fixed (in a collar or similar) then you have to change things a bit.

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P.E. Metallurgy, Plymouth Tube

 

[petar yovchev]

I applied a cantilever load. I pushed one side in a hole and step 30cm away from the hole with my body weight (90kg). Bending moment = 882.9N x 0.3m = 264.87Nm
(264.87Nm x 32)/(π x 1.2cm ^3)= 1561MPa. If add the shear and contact stress it must've exceed 1600MPa
I did that experiment in order to check the hardened steel strength myself as the information I found differs too much.
But if my result is correct why there is no such amount of strength in any of the steel properties lists.
But I prefer to believe rather on my eyes then the lists
Am I going to make a revolution in the engineering science?

 

[GregLocock]

Unbrako bolts are around that strength. I think in antediluvian units that is around 100 ksi, which is what submarines are made of.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[EdStainless]

Greg, 1500MPa is about 200ksi.

Did the end deflect about 40mm?
Are you sure that there was no permanent deformation?

I am sorry but unless this is some very special grade of steel I cannot imagine a 1/2" bar, 12" long, taking a 200lb end load without some set.

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P.E. Metallurgy, Plymouth Tube

 

[petar yovchev]

I'm absolutely sure in the values, I did it twice, there was no deformation at all. It's an ordinary hardened shaft, I don't know from what machine,I have plenty of scrap like that at home.
Today I tried with another metals and the results was also amazing.
-Drive shaft from a car Φ22 in bending 1600Mpa (my weight 90kg at 1.8m + weight of the lever)and probably more as I did not dare to broke it, because it can injure me

at the same way I obtained
-piece of concrete rebar Φ14, in bending - 1400MPa starts to deform.
-Threaded dowel (plain carbon steel) M14 in bending 800Mpa starts to deform
and
-Threaded dowel M8 (Φ6 inner) in tensile about 800Mpa tears (23000N force - my weight through a lever)
So I feel a bit confused, considering the difference with values of strength I've known

Who don't believe can try, it's pretty simple

 

[EdStainless]

The shafts could be case hardened. And given that the highest stress in on the surface that case would be helping support the load, even if the core strength is lower.

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P.E. Metallurgy, Plymouth Tube

 

[petar yovchev]

Next time I thing to test a shaft in torsion if find where to spline it.
Shafts OK but what about the low carbon steel shouldn't its ultimate strength be about 350Mpa(51ksi) not 800MPa (116ksi)

 

[TVP]

petar,

Automotive shafts for driveline and transmission applications are either surface hardened by induction heat treatment, or by case carburizing. Typical surface hardness is 59 HRC minimum, which means that a surface bending stress under maximum load should be less than ~ 2200 MPa. The strength of the part varies from the surface to the core depending on the steel grade and the details of the heat treatment.

 

[petar yovchev]

TVP,You probably mean it shouldn't be less than ~ 2200 MPa
And in conclusion I accept it's normal automotive shafts to withstand 1500+ Mpa.
But I wonder what is the predetermined stress in the design of high strength auto parts like drive shafts ets