Hi,
I want to do some fatigue calculations on a structure. Does anyone know where I can find a Wohler or SN curve for the material 42CrMo4 in the Q+T condition? I have done some google searches but nothing comes up. Any help would be appreciated.
This kind of information is not available for free on the Internet.
You can conduct a search of this site - many requests have been made for S-N curves for various materials. Check the printed publications mentioned in these threads.
For a large collection of materials information, including fatigue, look at ASM International:
I didn't check if their test was specifically for quenched and tempered, but this is the normal treatment for this material when used in driveshafts or whatever.
I was going to try to convert this data into a 'rolling contact SN curve' for use in a brg application. Some people believe this can be done reliably, others say it can't.
Rolling contact fatigue is highly dependent upon surface roughness, inclusion type and amount, case hardness, case microstructure (non-martensitic transformation products, intergranular oxidation, etc., retained austenite, carbide distribution, etc.), and residual stresses. The S-N curve that would be generated using the method described above is really only suitable for estimating fatigue life of simple components, not bearings, gears, springs, etc.
I would agree with TVP. I would not recommend using S/N fatigue data obtained from reverse bending, uniaxial loading and attempt to extrapolate this to rolling contact fatigue under multi-axial loading conditions. There are way too many variables in rolling contact fatigue.
There are other approaches required to calculate an effective stress range for rolling contact fatigue. Here is a paper that was published on rolling contact fatigue of railway wheels as an example of the complexity of the analysis;