Identification of the dynamic characteristics of a viscoelastic, nonlinear adhesive joint

In this paper, the nonlinear mechanical characteristics of an adhesive (Sikaflex-252) are identified over frequency range, using eigenvalues of nonlinear system and inverse eigen-sensitivity method and experimental data. Sikaflex-252 is selected as an adhesive which is mainly used as a joining medium (joint) in structural applications. In order to simulate the viscoelastic behaviour of the adhesive, the frequency dependent Young׳s modulus and damping coefficient are assumed in identification process leading to the updating process being repeated for different ranges of frequencies to identify stiffness and damping properties of the adhesive. Using the optimum equivalent linear frequency response function (OELF) concept, in order to realize the nonlinear nature of the adhesive, modal tests are performed under two different random excitation levels which illustrate the stiffness softening characteristic of adhesive which can have serious implications regarding dynamic stability of structures. Furthermore, based on the identified characteristics, the paper examines the possibility of tuning of the Standard Linear Solid model (SLS), in representing the adhesive viscoelastic behaviour. Results of this attempt proved that the S.L.S. model with tuned parameters significantly improves the fidelity of finite element (FE) model to experimental results.