MODELING TURBINE BLADE CRACK DETECTION IN SONIC IR IMAGING WITH A METHOD OF CREATING FLAT CRACK SURFACE IN FINITE ELEMENT ANALYSIS

Sonic Infrared (IR) Imaging Nondestructive Evaluation (NDE) technology has shown inherent advantages for defect detection in aircraft structures. It can image a wide area within a second or two for metal material targets. Due to high stresses aircraft engine turbine blades bear during their operation, fatigue cracks can form after a number of hours of service. Sonic IR imaging shows its great potential for this application. However, interaction of the sonic excitation and subsequent crack heating requires fundamental understanding of physical and thermal processes in complex geometries such as turbine blades. Simulation modeling can provide results to better understand contributions of some parameters where experimental arrangements are hard to produce. Because of the irregular shapes of turbine blades, their finite element analysis (FEA) models are always dominated by tetra elements. In the usual procedure of using tetra elements, it is very difficult to create flat crack surface in such complex shapes. A new method to create a flat crack surface is designed for an actual blade. In this paper, we will present data of modeling turbine blade crack detection with external ultrasound excitation as the results of applying this new method, guided by our experimental Sonic IR imaging study on the blade.