Hardness vs. Elastic Modulus

[DrewEven]

Hello, first post here...

I'm trying to calculate the contact stress between a metal pin and a flat metal plate. The pin is a 1045 steel that is through heat treated to a hardness of 45HRC. In order to calculate the contact stress between the pin and the plate using Hertzian's contact equations, I must know the elastic modulus of the 45HRC 1045 pin.

Without doing a tensile test on the part, is there a good way to correlate elastic modulus from a hardness measurement?

Regards,

Drew

 

[swall]

The elastic modulus of steel at any hardness level is 30 million psi.

 

[DrewEven]

I thought that the modulus of any steel (non heat treated) was 30 million psi. Doesn't the hardness measurement test the toughness of the material, i.e. the area under the stress strain curve? So by heat treating I'm only increasing the yield strength of the metal, not it's elasticity?

From college I thought that by modifying the amount of carbon in steel, you couldn't change the modulus, but I wasn't sure about the effect of heat treatment on Young's modulus.

 

[NickE]

Read this thread to find out why modulus is almost completely insensitive to heat treat or chemistry of metallic alloys.

thread330-87802


Nick
I love materials science!

 

[arunmrao]

If you have access to Mechanical Metallurgy by Dieter,you cansee that the E is a constant for steels and is not significantly affected by changes in chemical composition or heat treatment.

" All that is necessary for triumph of evil is that good men do nothing".
Edmund Burke

 

[EdStainless]

The only way to change E is with very severe cold work, and then it only changes slightly.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[DrewEven]

Ok, so I think everyone has confirmed to me that E doesn't change with increasing heat treatment, and only negligibly with cold working.

So I'm confused because I thought that hardness was essentially a measurement of a materials ability to resist deformation from a harder material, which seems to me like stiffness, i.e. Elasticity.

Any guidance on my mis-interpretations would be appreciated...

Thanks

 

[CoryPad]

Indentation hardness is the resistance of a material to indentation. There are elastic and plastic components to this, but the plastic component is much larger.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[EdStainless]

The amount of defection at low loads (no permanent deformation) is a function of geometry (I) and modulus (E).

The deflection limit at which you will start to get permanent deformation is a function of strength (proportional to hardness).

Two bars of identical geometry, one annealed 1005 and the other Q&T 4340, will deflect the exact same amount at light loads. The alloy steel bar will be able to defect much further before becoming deformed because it is stronger.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[Cormet]

I've seen Hardness Vs. Tensile Stregth (for carbon steel)
i API RP 579.

Cormet

 

[DrewEven]

OK, thanks to everyone for the help on the clarification of hardness vs. elastic modulus.

Now I'm running into another issue for my calculation which is trying to predict the yield strength of a cold worked part. The part is a hollow tube, extruded from 1020 steel, and then has two slots pierced into its sides. I'm running Hertzian equations to predict the compressionial stress for the given loading scenario that we have on the slots(cylinder on flat plate), but I'm predicting quite large failure on the softer 1020 tube, but in fact there is no failure there, I supspect because the slot is highly work hardened in that area.

So, is there a good way to theoretically calculate the local yield strength in the slot area, or should I simply try to take the hardness on that slot (easier said than done) and try to correlate that to a yield strength?

Any help is extremely appreciated...

Thanks! - Drew