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bsmet95 (Mechanical) (OP)
12 Feb 09 13:14
When the pressure of a wheel or cam rolling on a flat surface (or any surface) has been calculated, how does one know what the allowable stress for a particular material should be? Is the allowable stress a percentage of the Ultimate or Yield stress?
Helpful Member!  TVP (Materials)
12 Feb 09 16:59
bsmet95,

The allowable surface pressure (also called contact stress) will be a multiple of the yield stress, not a fraction of it.  As an example, Hertzian contact stresses for gears and bearings may be > 2000 MPa and still be considered within the allowable design requirements for high cycle loading (see ANSI/AGMA 2001-C95, ISO 6336-1, etc.).  Perform a keyword search for contact stress or look through some machine design textbooks.
TVP (Materials)
12 Feb 09 17:19
Helpful Member!  israelkk (Aerospace)
12 Feb 09 21:05
In ball and roller bearings the contact stresses can go up to 580,000 psi (408 kgf/mm^2).
Kwan (Aerospace)
12 Feb 09 21:26
Search this forum for MMPDS.  Contains FBRU/FBRY for many materials.
After13urneR (Mechanical)
18 Feb 09 7:19
isrealKK,  Where did you get the 580,000 psi from?  Where can I find the maximum allowable contact stress pressure for C1045 steel?
CoryPad (Materials)
18 Feb 09 8:28
MIL-HDBK-5 (now MMPDS) contains information on bearing strength, which is a form of allowable surface pressure.

The handbook is available free at ASSIST:

http://assist.daps.dla.mil/quicksearch/

The latest version of MMPDS is available for purchase from multiple sources:

http://projects.battelle.org/mmpds/new_page_12.htm
TVP (Materials)
18 Feb 09 10:58
After13urneR,

The value that israelkk mentioned is for high strength, case hardened alloy steels used in bearing applications (SAE 52100 or better).  A carbon steel like 1045 can be induction hardened to achieve high surface hardness, but it will not have the same allowable contact stress.  In what condition do you intend to use the 1045?  Quenched and tempered?  As cold-drawn?  Something else?
After13urneR (Mechanical)
18 Feb 09 12:03
TVP,

The C1045 is induction heat treated and tempered to Rockwell C-45 to C-55.  This has been good for this application in the past, but I am designing some new rollers and would like to know I've checked everything.  I would like to get my hands on a table (machinery's handbook style) that shows what the allowable contact stress pressure is for my rollers.  Thank you for the help.

 

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