Numerical Investigation on HCF Weak Link Locations of a Wide-Chord Laminated Composite Fan Blade With Coupled Modal Vibrations

High cycle fatigue (HCF) of laminated composite fan blade (LCFB) caused by vibration is important content within airworthiness certification. This paper proposed a method suitable for LCFB to evaluate its HCF failure location under complex excitations. First, a high-fidelity finite element model (FEM) of LCFB was built and the classification of modal shapes was carried out. By setting the resonance margin threshold on the campbell diagram, the modal superposition vibration that may be excited at the common rotation speed was found out. Then, a postprocessing strategy was proposed to evaluate HCF weak link locations. Constant life diagrams (CLD) for the unidirectional lamina were employed to determine the HCF weak link location of LCFB in combination with the steady and vibratory stresses along the corresponding material principal directions. For the coupled mode vibration, the HCF weak link locations with different stress components were calculated and the critical failure stress component was identified. For the coupled mode vibrations, the HCF weak link locations with the resultant stresses were calculated with different combination of modal participating coefficients. The results indicated that the HCF weak link locations may change to locations different from that in single mode vibration. Furthermore, the critical failure stress components may be transferred to directions with larger vibratory stress margins. This work presented a useful numerical technique to study the effect of mode coupling on LCFB HCF characteristics under complex operating conditions.