Effect of plasma nitriding of a stop hole along the fatigue crack path on crack propagation

The effect of nitriding of the fastener hole along the Fatigue Crack Growth (FCG) path on FCG was investigated. A standard Compact Tension (CT) specimen made of AISI 4140 steel with a 5 mm diameter hole drilled on the FCG path was used. It was subjected to a plasma nitriding process. Crack growth was monitored using the digital imaging method. The results were compared with the paired sample t-test. As compared to the un-nitrided sample without a hole (control group), FCG lifetime was increased 1.5 times un-nitrided without a hole and nitrided with a hole samples. And 2.5 times the total FCG lifetime was observed in drilled un-nitrided samples. It was determined that nitriding treatment of the drilled samples eliminated the positive effect of the hole on FCG life.