Abstract: A military aircraft, which had serviced for more than twenty years and retired recently is torn down and then inspected. It is found that there are corrosion pillowing cracks in lap joints. By use of three-dimensional finite element method (FEM), stress and strain distributions of lap joints with semi-elliptical cracks of aircraft structure are analyzed, and 20-node singular isoparametric element is used. By calculating the stress intensity factors (SIFs) of typical locations around the crack tip, its growth direction is predicted, and its effect on the structural integrity of aircraft is analyzed. The results show that semi-elliptical crack with small aspect ratio’s (a/b) will not break the outside surface. So they are hidden, and there is potential danger to the safety of aircraft.

Key words: lap joint, crack, stress intensity factor, corrosion, finite element method