Notes on Fatigue for Pure Compression Stress

Fatigue is usually associated with tensile stresses.

Engineering knowledge of compressive fatigue is very limited. Compression stresses do not cause cracks, but plastic compressive strain can cause tension stresses when the load is returned to zero and the resulting tension stress causes cracks.

* * *

R = min stress/max stress

But R ->   – infinity   for pure compression stress and with max stress->0

MIL-HBBK-5J S/N curves are typically given for a family of R values starting at a lower limit of R=-1, which is the fully-reversed stress case with zero mean stress.

So MIL-HBBK-5J is not useful for pure compression.

* * *

Compressive residual stresses can be introduced in the surface by shot peening to increase fatigue life.

* * *

More later…

 

– Tom Irvine

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