Evaluation of Critical Crack Orientations and Crack Growth Analysis in Compressor Blade Root Subjected to Fatigue

Aero-engine compressor blade and disk assemblies are subjected to radially outward centrifugal force due to blade rotation and the bending of the blade due to gas pressure. Static analysis is done initially to find the critical crack orientation at the root of the blade. With simulated initial cracks, the cracks are allowed to grow in low cycle fatigue (LCF) and isochromatics are captured at selected intervals. Using digital photoelasticity, isochromatic images are used along with an over-deterministic least-squares approach to find the fracture parameters. As the stress fields are very complex, a multiparameter solution with a higher number of parameters was needed to model the stress field. Crack growth angles are evaluated using maximum tangential stress (MTS), strain energy density (SED), and generalized MTS (GMTS) criteria. It is observed that the GMTS criterion predicted closer results to that of experimental values, which implied the significance of T-stress in predicting the crack growth angle.