The high or medium speed diesel engine of the ships have the reduction gears in general to fit the high or medium rotating speed of the engine to the relatively low rotating speed of the screw propeller. In this case, the highly flexible elastic coupling is installed in the power driving shaft system to protect the reduction gears from the explosive forces of the engine.
The rubber elastic couplings are widely used in the power driving propulsion shaft system because of the high flexibility of rubber materials and the low manufacturing price.
The rubbers are visco-elastic materials and the relation between the stress and strain in non-linear and dependant to the strain rate. So, the torsional stiffness of the rubber elastic coupling is changed according to the frequency and the amplitude of the fluctuating transmitted torque. To estimate the vibration characteristics of the propulsion shaft system, the exact dynamic torsional stiffness of the elastic coupling is necessary in the operating frequency range.
Is this study, the dynamic characteristics of the rubber materials are investigated to use on the basic data in calculating the dynamic torsional stiffness of the rubber elastic coupling. The several mathematic models are suggested to understand the stress-strain relation. The stress relaxation function and the creep function are also presented for every mathematic models.
The standard linear model is adopted to show the vibration response characteristics of elastic coupling rubber and the experimented method is presented in this paper to obtain the material constants. The forced vibration system is designed and manufactured for experiment of this study, The 3 examples of NBR, Viton and Si rubber are investigated to obtain material constants and their variation trends according to the frequency are shown. The energy dissipations are also shown as the function of frequency.