Calculate number of cycles to fracture:
If the plastic deformation is taken into consideration calculate number of cycles to fracture in above Example.
Solution
Δ K I eff / Δ K I = 0.5 + 0.4 R
where, R =s_{min}/s_{max} = 30 /70 =0.43 and Δ K = 71√a
Δ KI eff = 71√a (0.5 + 0.4x0.43)
= 71 x 0.67√a 47.67 √a N/mm^{2 }^{ }
∴ da /dN = 10^{- 8} (47.67 )2.0 = 2.273 x 10^{- 5} a
∴
∴ N _{f}= 44003 x ln 146.14 /35= 44003 x 1.43 = 62890 cycles
Note that due to plastic deformation in crack tip zone there is more than 100% increase in fatigue life.