Modelling of constrained thin rubber layer with emphasis on damping

摘要

Noise and Vibrations is an environmental problem that takes considerable resources into account from the engineering community. Other expectations arising from an environmental perspective is to reduce weight of vehicles, aircrafts, ships etc. Requirements within these two areas are difficult to meet in combination. Efficient and accurate methods for predicting noise and vibration levels is key to understand how to optimize products and solutions given the full spectra of requirements. Rubber is widely used in combination with metal constructions to achieve damping and thereby reducing noise and vibration levels. A common and efficient configuration for reducing vibrations is that of a thin rubber layer bounded to a vibrating shell structure and constrained by a cover metal layer. This configuration is commonly denoted constrained damping layer. The fundamental principle is to reduce vibrational energy of the host structure by deforming the viscoelastic layer in shear. This paper outlines a procedure for an efficient way of modelling sandwich type steel-rubber-steel components with high accuracy. The rubber used in the study is a "Nitrile" type rubber (acryl-nitrile-butadien). Material characteristics are identified using a standard procedure where a cantilever specimen is excited with a harmonic load at different temperatures. Then we apply fractional order viscoelastic theory in order to set up a constitutive model by applying a least square fit to experimental dynamic shear data. The steel-rubbersteel system is then modelled by using the finite element method (FEM) where a special interphase element is developed representing the rubber layer, where the displacement field of the rubber has been expended into a power series in the thickness direction. This technique makes it possible to achieve a high resolution of the displacement field in the thickness direction without adding more degrees-of-freedom in this direction. We then study the dynamic response of a cantilevered specimen which is compared with experimental data and another FEM code. Finally, the dynamic response of a quadratic free-free sandwich plate is calculated and compared with experimental data. We find the results very encouraging.