Modelling of Short Crack Arrest and Fatigue Propagation Using Non-local Fracture Criteria

Abstract

The prediction of the short crack behavior at the critical parts of gas turbine engines under cycle load is one of the major challenges in the aerospace industry. The total service life of the critical parts can be significantly affected by short crack growth regime. The short crack demonstrates different behavior during fatigue growth in comparison with long crack. Therefore, the prediction of the crack propagation life based on standard linear fracture mechanics methods can lead to non-conservative results in the life assessment of critical parts. The size of the physically short cracks is comparable with the material grain size for nickel and titanium alloys, which are widely used in aerospace industry. Also plastic zone near the crack tip has similar or bigger size in comparison with short crack size in high stressed features of compressor and turbine discs. Both parameters are key factors which determine the short crack arrest and propagation mechanism. The theoretical concept of the fatigue short crack growth and arrest phenomena, which is suggested in current work, is based on taking into account the material microstructural parameters and material plastic behavior. The suggested theoretical model requires a minimum number of material parameters which usually well-known i.e. yield stress, grain size, endurance limit and Paris law crack propagation constants. This proposed analytical method has been validated based on experimental data for selected applications.