Effecting on crack propagation behavior due to residual stress and defects in aluminium alloy

For cracks under mode I and mixed-mode conditions in aluminium ally, it was studied effecting on direction of crack propagation due to residual stress and defects. Stress intensity factors KI and KII were calculated by finite element method (FEM) analysis with a ideal crack in a finite plate, corresponding with a experimental crack. So the direction of crack propagation could be predicted using the maximum tangent tensile stress criterion proposed by Erdogan-Sih. As a result, the crack propagation paths predicted by FEM were in good agreement with the experimental results, either mode I nor mixed-mode cracks. That is the direction of crack propagation was determined by the cyclic component of stress intensity factors, but it had nothing to do with the residual stress. On the other hand, effect on crack propagation life due to residual stress near the crack was discussed using the specimens with defect. It was found the crack propagation life increased while residual stress attached in the specimen. Finally, relationship between crack propagation life and effective stress intensity factor was evaluated and it demonstrates in good agreement with the crack BCS theory.