Abstract: t was found in fatigue experiments to main landing gears that circular surface cracks occur on the shock absorbing cylider of the struts and propagate rapidly. For estimating the propagtion life of the cracks this paper presents calculating methods of a swell factor and stress intensity factor of circular surface cracks on the cylinder. These are based on formulas of stress intensity factors of surface cracks of plates and swell factors of through cracks of cylinders. This paper recommends calculating formulas of fatigue crack propagation in service environment and gives relevant parameters’ values of 30CrMnSiNi2A.

Key words: landing gear, cylinder, crack propagation