Mode-converted Lamb wave sensitivity prediction for part-thickness crack-like defects

Fatigue crack growth is one of the most common damage types in aluminum components, widely used in aircraft \nstructures. Detection of fatigue cracks at an early stage is important to guarantee aircraft safety. Efficient non-destructive \nevaluation (NDE) and structural health monitoring (SHM) can be achieved by employing low frequency guided \nultrasonic waves, as they can propagate long distances along plate structures. SHM systems using distributed guided \nwaves sensors have been proposed for efficient monitoring, but have limitations due to environmental influences such as \nthe temperature stability of the conventional baseline subtraction method. The scattering and mode conversion of guided \nwaves at part-thickness defects was investigated to quantify the sensitivity for defect detection and the potential for the \ndevelopment of a baseline-free SHM methodology employing mode converted guided waves. Baseline-free SHM \nmethodology employing mode conversion is expected to overcome some of the limitations caused by environmental \nfactors and to improve sensitivity and stability by employing new or modified signal processing algorithms. A three \ndimensional (3D) Finite Element (FE) model was developed to predict the mode conversion of the fundamental guided \nwave modes. The influence of defect length and depth on detection results were investigated numerically. The detection \nsensitivity for part-thickness defects in a plate is quantified.