Allowable bearing/contact stress 2

[bsmet95]

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?

 

[TVP]

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]

Here are just a couple of .pdfs that have some information on contact stress/allowable stress:

http://www.geartechnology.com/pa/members/julyaug05/section9.pdf

http://www.ees-kisssoft.ch/downloads/037.pdf

http://www.kumera.com/documents/Girth_gear_manual.pdf

 

[israelkk]

In ball and roller bearings the contact stresses can go up to 580,000 psi (408 kgf/mm^2).

 

[Kwan]

Search this forum for MMPDS. Contains FBRU/FBRY for many materials.

 

[After13urneR]

isrealKK, Where did you get the 580,000 psi from? Where can I find the maximum allowable contact stress pressure for C1045 steel?

 

[CoryPad]

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]

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]

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.