An interpolated FFT algorithm for full-field nonlinear modal testing with a 3D-SLDV

The measurement of full-field dynamics of a light-weighted structure can be challenging due to its low mass-to-area ratio, complex spatial deformation shapes and geometrical nonlinear behaviours under harsh loadings. In this paper, a Three-dimensional Scanning Laser Doppler Vibrometer (3D SLDV) is used to capture the full-field, multi-harmonic shapes of a vibrating blade in a laboratory environment. The wellknown disadvantages of the 3D SLDV such as its long testing duration, coarse frequency resolution and severe spectral leakage are countered by a Multi-step Interpolated Fast Fourier Transform (Multi-step IFFT) procedure in combination with a phase resonance testing strategy. A numerical example featuring ten harmonics is firstly presented, highlighting the accuracy of the proposed procedure before it is applied to the test of a wide-chord fan blade. To the best of authors’ knowledge, the full-field, multi-harmonic shapes for such an industrial large-scale, geometrically complex and nonlinear structure are experimentally measured for the first time.