Fracture Parameters of Surface Cracks in Compressor Disks

The elastic and elastic-plastic fracture mechanics parameters of surface cracks in compressor disks of aircraft engines are evaluated using both the finite element method and the weight function method. First, a three-dimensional finite element model of a low-pressure compressor disk containing a surface crack at the snap radius is developed. The stress intensity factor distributions along the surface crack front with various crack shapes and sizes in the disk under a typical engine operation condition are calculated. Then, the effect of biaxial stresses on the stress intensity factor of a crack emanating from a tie bolt hole in a representative compressor disk is investigated using the weight function approach. Emphasis is given to determining the effect of the bolt hole plastic zone on the fracture parameters when the compressor disk is highly loaded. Finally, a new theoretical model for the estimation of the fracture parameters of a through-thickness crack in the web region is proposed using a definition of local biaxial stress ratio. The studies show that the developed model can provide better estimation of the plastic zone size and the crack-tip opening displacement than those existing models.