Hertz contact stress
Hertz contact stress
(OP)
Please can anyone help with using Hertz contact stresses? I am designing some equipment for a customer who requires I use a safety factor of 4 on proof strength and 6 on ultimate strength. This is fine when it comes to bending and shear stresses etc, however I'm not sure "what to do" with Hertz stresses. Part of the design uses a hardened steel roller, dia 12 mm, (440C, UTS 930MPa) on a flat steel plate (En24T, proof 650 MPa UTS 850 MPa), loaded both statically and slow moving. I've calculated the compressive and shear stresses according to Roark Table 33 case 2a, however I don't know what to do with them! They are 504 MPa and 168 MPa. I've done the American Railway Engineering Association allowable loading check from the text and my loading has a reserve factor of over 4.
Cheers.
Cheers.





RE: Hertz contact stress
prex
http://www.xcalcs.com
Online tools for structural design
RE: Hertz contact stress
RE: Hertz contact stress
Take the Hertz contact stress intensity (surface stress), divide it by 4 if it is a linear contact (cylinder onto flat) and compare the result to your allowable.
prex
http://www.xcalcs.com
Online tools for structural design
RE: Hertz contact stress
Cheers
RE: Hertz contact stress
The shear stress limit is generally half the allowable stress intensity limit. If you're comparing bending stresses, for example, with a quarter of yield then by the same token the shear stress should be compared with one eighth of yield.
corus
RE: Hertz contact stress
Prex - could you please give me a reference for your advice "The limits normally adopted for Hertz's contact stresses are 4 times the allowable stress for linear contact and 5.5 times for point contact"? I need to write up my calcs and submit to my customer.
RE: Hertz contact stress
fd is the calculation strength or allowable stress.
prex
http://www.xcalcs.com
Online tools for structural design
RE: Hertz contact stress
ASME B&PV Code Sec IID allows 1.6xDesign Stress for Bearing Stress on Pressure Vessel Design
RE: Hertz contact stress
Cheers
Rattler
RE: Hertz contact stress
I have not seen definitive answers.
Ball bearings are often life tested with
stresses in the 350000 PSI range.
The 350000 is more than 2.5 times the
UTS of the bearing rings materials
which have uts values around 123000 PSI.
These are surface pressures and not
bending stresses but bearing stresses.
I have also seen unusually high surface
stresses in gears without failure.
I think bearing stresses are published for
some materials. Surely they exceed the
uts of the materials.
RE: Hertz contact stress
RE: Hertz contact stress
RE: Hertz contact stress