A new detection method for structural non-linearities

It has been observed that during a modal test of a structure, various forcing levels involving broadband excitation cause the FRF estimates to show non-coherent behavior over a certain frequency range. Even if it is believed that these distortions are caused by structural non-linearities rather than digital signal processing, a solid detection method is still not available. This paper proposes a method, which is able to determine whether structural non-linearities are indeed the source of the observed FRF and coherence distortions. This is done by formulating a new coherence function (combined coherence, CCOH) using temporal and spatial information. After explaining the physical significance/meaning and computation of the new combined coherence, this new detection method is applied to a 4-DOF simulation model in several non-linear test cases.