Fatigue Crack Propagation in Steel Weldments

Fatigue tests have been conducted on low carbon steel butt welds containing lack of penetration defects. The growth of fatigue cracks from the lack of penetration defects was monitored by radiography. These measurements allowed the total fatigue life to be separated into periods of crack initiation and crack propagation.

It was found that the rate of crack growth conformed to the expression: The initiation period was found to occupy approximately one-half of the total fatigue life and to consist of the cycle necessary to shake down the residual stresses in the weld and to form the lack of penetration defect into an active fatigue crack.