FRF estimation on rotational DOFs by rigid block attachment approach

Measurement of frequency response function (FRF) has been limited to translational degrees of freedom (DOFs), which restricts the applicability of experimental modal analysis. This paper proposes a new estimation method of FRF on rotational DOFs. In the proposed method a T-shaped rigid block is attached to structure's measurement point; the block is excited by conventional impact hammer; and the rotational FRF as well as translational FRF with respect to the measurement point are estimated after the numerical procedure. It is shown that the FRFs are free from the inertia effect of the T-block. The feasibility of the method is investigated by applying it to a beam structure. The FRFs including the rotational DOFs are estimated. They are used for the prediction of the FRFs of an integrated structure by substructure synthesis approach. The predicted FRFs are compared to FE analysis and also compared to the prediction in which rotational DOFs are excluded.