Spatially Resolved Experimental Modal Analysis on High-Speed Composite Rotors Using a Non-Contact, Non-Rotating...

Area of Science:

• Mechanical Engineering
• Materials Science
• Structural Dynamics

Background:

• Fiber-reinforced composites are crucial for lightweight, high-speed rotating machinery like turbomachine fan blades.
• In situ structural dynamic analysis during rotation is essential for rotor safety and performance.
• Current methods often require co-rotating sensors, posing practical challenges.

Purpose of the Study:

• To develop and validate a non-contact, non-rotating sensor approach for measuring spatially resolved vibration responses of rotating structures.
• To enable unambiguous identification of natural frequencies and mode shapes without co-rotating sensors.
• To advance in situ structural health monitoring for composite rotors.

Main Methods:

• A novel method using a non-contact, non-rotating sensor system (diffraction grating-based) was employed.
• Consecutive measurements with a constant excitation function and varying time delays increased sampling frequency.
• Deflection measurements were taken on a fiber-reinforced polymer disk at various surface speeds (up to 300 m/s).
• Validation was performed using strain gauges.

Main Results:

• The non-contact method successfully measured spatially resolved vibration responses.
• Resulting spectra correlated well with data from co-rotating sensors (strain gauges).
• A rotation-induced increase in two natural frequencies was observed, with mode shapes derived at operational speeds.
• Measurement uncertainty was below 15 μrad for the primary sensor system.

Conclusions:

• The developed non-contact method offers a paradigm shift for analyzing rotating composite structures.
• It allows for accurate, unambiguous determination of natural frequencies and mode shapes.
• This technique enhances the safety and performance assessment of components like turbomachine fan blades.