The fracture of structures under mixed-mode loaded cracks is usually assessed using stress intensity factors (SIF). Domain integrals, specially the \J-integral and the interaction integral, are widely used for SIF extraction and provide high accurate estimations with finite element methods, although the \J-integral does not allow the separation of the SIF components. However, interaction integral definition implies hypothesis that are not fulfilled in generic non-planar cracks and therefore other methods can be an option to solve this problem. A different path independent integral, the neutral action integral, was introduced in 2010 by Kienzler et al. The application of the \J-integral and the neutral action integral allows the computation of the SIF in a mixed mode situation and separate the SIF components. The presented study considers the applicability of the neutral action integral and investigates its limitations. The research is performed using well known and basics problems, that can be considered as a basis for other more complicated cases, in order to obtain an convergence analysis without introducing further errors