How to measure strain & stress in lab gears?

[meemouk]

When deriving S-N curves for gears, is stress calculated from the torque value applied or is it common to use strain gauges?

Also, would the results of testing dog-bone shaped coupons under cyclic loading be representative of the material fatigue model? or do you have to test actual gears to get an accurate representation of the gear's material damage curves?

 

[CoryPad]

For us (an automotive driveline supplier with multiple billions of dollars in sales), we use the torque unless it is a research project.

The dog bone specimens can be used to determine material fatigue behavior, and that can be used to analyze the gear performance. We usually test complete parts since that is necessary for other reasons.