Continuous critical loading of pressure equipments can affect the structural stability of these plants. The structural stability and mechanical resistance under pressure loads can also be affected by defects. Fracture mechanics assumptions were applied to aluminium alloys to study their effect on its mechanical behaviours. A 3-point bending standard test was employed and the critical Stress Intensity Factor, K (SIF) in mode I was determined in order to provide a quantitative/qualitative evaluation of the performance. Additional experiments were carried out to validate the numerical results gained from the Finite Element Method (FEM) and the Extended Finite Element Method (X-FEM). The crack propagation process is discussed in this study focussing on the effect of crack tip radius.