Hertzian contact stress SS-2244 / AISI-SAE 4140

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Discussion Overview

The discussion revolves around the maximum allowed Hertzian contact stress for materials SS-2244 and AISI-SAE 4140, focusing on potential failure modes, material properties, and calculations related to contact stresses. Participants explore theoretical and practical aspects of these materials in the context of engineering applications.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant seeks information on the maximum allowed Hertzian contact stress for SS-2244 / AISI-SAE 4140, noting difficulty in finding relevant data.
  • Another participant provides material properties for AISI-4140 at room temperature, including various strength values, but questions the failure criteria related to contact stresses.
  • A participant describes a specific application involving a pin and hub, detailing dimensions and the goal of calculating the maximum force without causing plastic deformation.
  • Some participants express uncertainty about the provided strength values, suggesting they may pertain to heat-treated conditions rather than the annealed state.
  • Discussion includes comparisons between AISI-4140 and AISI-4130, noting differences in strength and common usage based on diameter.
  • Participants propose a range of values for bearing strength, suggesting approximations for calculations based on whether the material is heat-treated.
  • There is mention of the need for additional material properties such as elastic modulus and Poisson's ratio for Hertzian stress calculations.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the maximum allowed Hertzian contact stress values, with multiple competing views on the material properties and their implications for the specific application discussed.

Contextual Notes

Limitations include the lack of clarity on the heat treatment state of the materials discussed and the need for further definitions regarding failure criteria and material properties relevant to the calculations.

Ian06
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Hello guys!


Is there anyone who knows where i can find information about maximum allowed Hertzian contact stress for material SS-2244 / AISI-SAE 4140 or any similar material quality?

I have been searching for this information in several Swedish books and material tables, without success.
 
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Can you give us some more information on the potential failure mode?

AISI-4140 Low Alloy Steel at room temperature
F_tu = 150 ksi
F_ty = 132 ksi
F_cy = 145 ksi
F_su = 90 ksi
F_bru = 219 ksi
F_bry = 189 ksi

t = tensile; c = compressive; br = bearing; u = ultimate; y = yield
 
You need to define what your failure criteria is, especially with contact stresses.
 
A pin made of high grade spring steel is pressed tangential against the inside of a hub.

Pin diameter (r1) = 2,5 mm
Hub diameter (r2) = 55 mm (concave, and therefore -55 mm in Hertzian calculations)
Contact length = 40 mm
Hub material SS-2244 / AISI-SAE 4140

The objective is to "backwards" calculate the maximum force F (N) that can be applied without causing plastic deformation on the inside of the hub.

I´ll draw a simple sketch and add it tomorrow.

Unfortunately my english is rather bad.
 

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minger said:
Can you give us some more information on the potential failure mode?

AISI-4140 Low Alloy Steel at room temperature
F_tu = 150 ksi
F_ty = 132 ksi
F_cy = 145 ksi
F_su = 90 ksi
F_bru = 219 ksi
F_bry = 189 ksi

t = tensile; c = compressive; br = bearing; u = ultimate; y = yield

Thank you minger! Do you have any reference (book/website etc.) for this information?
 
minger said:
Can you give us some more information on the potential failure mode?

AISI-4140 Low Alloy Steel at room temperature
F_tu = 150 ksi
F_ty = 132 ksi
F_cy = 145 ksi
F_su = 90 ksi
F_bru = 219 ksi
F_bry = 189 ksi

t = tensile; c = compressive; br = bearing; u = ultimate; y = yield
That seems awfully high for 4140 in the annealed state. Are you sure that isn't in some heat treated condition? The OP didn't mention anything about the final condition so this may be correct.
 
Oh, the 2.5mm (roughly 0.1") makes a difference. The spec I quoted was for 1" or greater...

Nope, that is for less than 1". It should be good if it is 4140. It seems that for smaller diameters, AISI-4130 is more commonly used, which is significantly weaker.

Some comments:

AISI 4130 is a chromium-molybdenum steel that is in general use due to its well-established heat-treating practices and processes techniques. It is available in all sizes of sheet, plate and tubing. Bar stock of this material is also used for small forgings under one-hal finch in thickness. AISI-4135 is a slightly higher carbon version of AISI 4130, is available in sheet, plate and tubing.

AISI 4140 is a chromium-molybdenum steel that can be heat treated in thicker sections and to higher strength levels than AISI 4130. This steel is generally used for structural machined and forged parts one-half inch and over in thickness. It can be welded but it is more difficult to weld than the lower carbon grade AISI 4130.

OK, so agreed Fred, without a little more material information, it's hard to tell. Let me get the other source. OK, 1" round bar has
Annealed - F_ty = 62ksi
Normalized - F_ty = 93 ksi

You're probably looking at a bearing strength, so for bar, forgings
Annealed - no data
Normalized - 158 ksi
Normalized and heat treated (with Ftu = 140) - 225 ksi
Normalized and heat treated (with Ftu = 160) - 252 ksi
Normalized and heat treated (with Ftu = 180) - 284 ksi

edit: Ian, my first source is a MIL spec manual called the MMPDS (Metallic Materials Properties Development and Standardization). It's a slightly more current version of something that was called...(something else can't remember). We just 'have' it, although I do know for fact that it is available from off of a website hosted by a Big10 school that makes a name for itself with engineering.

I also use the ASMD (Aerospace Materials Database), which we have both in several extremely large old books, and as an online website we need to log into.
 
So a value between 140-284 ksi will work as an approximation for calculations with the 2,5 mm pin?
 
I would say 158 ksi if its not heat-treated, 225 if it is.

Since you're doing Hertzian stress, you're probably going to need elastic modulus and Poisson's huh?
 
  • #10
minger said:
I would say 158 ksi if its not heat-treated, 225 if it is.

Since you're doing Hertzian stress, you're probably going to need elastic modulus and Poisson's huh?

Yes please! :smile:
 

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