Crack closure effects during low cycle fatigue propagation in line pipe steel: An analysis with digital image correlation

• Crack propagation under LCF was investigated in a X65 linepipe steel.
• Crack closure under LCF was characterized with DIC displacements.
• Measured closure levels were lower than those calculated by analytical models.
• Experimental results were analyzed with a ΔJeffJeff-based model.
• Experimental closure levels allowed a good fatigue life prediction.

Fatigue crack growth was investigated in a line pipe steel. Severe straining conditions, like those experienced by pipelines, were considered during the experiments. Crack closure effects were investigated during the tests by adopting an innovative technique based on digital image correlation. Experimentally measured crack closure levels were implemented in a crack propagation model based on elastic–plastic fracture mechanics. A modified formulation of ΔJeffΔJeff, necessary to accurately describe crack propagation driving forces, is presented and employed to assess fatigue life in presence of high plastic strains.