1992 Volume 78 Issue 4 Pages 640-646
The effect of varying stress on fatigue life under cathodic protection by a zinc sacrificial anode and freely corroding condition in synthetic sea water and in air was investigated using 800 MPa grade high strength steel notched specimens ( Kt= 3.5 ).
The main results obtained are as follows:
1) Under a constant stress amplitude (CSA), fatigue lives in sea water under cathodic protection are shorter than those in air. However, under two step stress amplitude (TSSA ), fatigue lives under cathodic protection are rather longer than those in air.
2) In a low stress amplitude region, fatigue lives under TSSA are shorter than those under CSA in air and under cathodic protection.
3) Even when the higher stress amplitude in TSSA is much lower than the values shown by the S-N curves under CSA, the failure of notched specimens occurs.
4) Under the free corrosion potential, there is no difference in fatigue lives between under TSSA and under CSA, and Miners rule exists between them.
5) Under TSSA, macroscopic crack growth rate is retarded in air and under cathodic protection, and the effect of TSSA on macroscopic crack growth is in reverse to that on crack initiation and microscopic crack growth.
