DIC-based structural strain approach for low-cycle fatigue assessment of AA 5083 welded joints

The aim of this research was the development and application of the following structural strain approaches for predicting the low-cycle fatigue life of AA 5083 welded joints: Finite Element equivalent structural strain approach and Digital Image Correlation equivalent structural strain approach. The first one was already applied for the low-cycle fatigue life prediction of welded joints, while the second approach is here proposed for the first time. Low-cycle fatigue tests were conducted at displacement ratios equal to minus one and zero. The Digital Image Correlation technique was used to analyze the local behaviour in proximity of the welded fillet and to obtain a notch equivalent strain range-number of cycles curve. Furthermore, a complete indipendent experimental procedure to evaluate the equivalent structural strain range, using the Digital Image Correlation technique, was proposed. A Finite Element analysis, with the advantage of being mesh insensitive and requiring only the elastic parameters, was performed in order to apply the Finite Element equivalent structural strain approach. The two structural strain approaches were used to predict the fatigue life, obtainining good agreement with the ASME mean curve representing over 1000 experimental data.