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.
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