Abstract This paper presents a new method for identifying the nonlinear parameters of a connection used to couple two structures. The proposed Nonlinear Internal Force Identification Method (NIFIM) calculates the nonlinear internal forces and the corresponding relative displacements at the nonlinear connections by using the measured nonlinear responses of the system in the frequency domain. The method requires the measured nonlinear frequency response functions (FRFs) of the coupled structure, as well as the FRFs of the underlying linear system. In practical jointed systems, the linear FRFs correspond to the “stuck” mode of the nonlinear dry friction elements and can be obtained experimentally under low-amplitude excitation or computed numerically. The identified nonlinear internal forces are then used to estimate the relative displacements at joint degrees of freedom, and the parameters of the nonlinearity are obtained. The proposed method eliminates the need for measurements at the connection DOFs, a benefit of the technique as it is often difficult, if not impossible, to make such measurements in many engineering applications. The formulation developed to identify the joint forces at the connections requires measurements either at a single frequency with different excitation force amplitudes or at several frequencies in a specific range with a single excitation amplitude. The paper presents three case studies based on simulated experiments to demonstrate the performance of the proposed method and its sensitivity to measurement errors. These case studies include a lumped parameter system with dry friction nonlinearity and finite element models of two beams connected by a single bolted connection, and three bolted connections. The results show that the proposed method is robust to measurement noise and can accurately identify the nonlinear parameters of the connection.
Ahi et al. (Sun,) studied this question.