Damping Of Bolted Beams With Unequal Thickness Ratio

Abstract

Rapid development of structural members requiring high damping possesses a big challenge to the designers. An extensive study on the dynamic behaviour of these structures is required in order to assess their damping capacity. This study further helps the designers to know the parameters affecting the dynamic characteristics of these members. Improvement of damping capacity is one of the vital characteristics for these structures. Usually, the structural members have inherently low damping capacity. The damping capacity of a structural member can be enhanced using various techniques such as; inserting visco-elastic layers in between two layers, manufacturing sandwich structures and layered jointed structures. The jointed
structures usually provide adequate damping due to micro-slip and friction at the interfaces. Jointed structures are manufactured with the help of fasteners such as bolts,
rivets or welds. The bolted structure gives maximum damping compared to the other fasteners. The main source of damping in bolted structures is the energy loss due to friction and micro-slip at the interface of two layers. The damping capacity of the jointed structures mainly depends upon a number of parameters; length of the beam, thickness ratio, tightening torque on the bolt, and number of layers etc. When a dynamic load is applied on a bolted layered beam, it
vibrates with some amplitude of excitation at a particular frequency of vibration and the damping in this type of structure is achieved by the energy dissipation. It is
established that 90% of energy dissipation in jointed structure takes place due to micro-slip at the interfaces.
In the present work energy approach has been used to evaluate the damping capacity of structures. Euler-Bernoulli beam theory has been applied as the dimensions of the test specimens satisfy the criterion of thin beam theory. A theoretical equation has been derived to evaluate the damping capacity of the jointed cantilever structures. An
experimental set-up has been developed and experiments are conducted with a large number of specimens under different vibrating conditions to authenticate the theory developed. The logarithmic decrement technique has been used for measuring the damping capacity of the structures with the help of a digital storage oscilloscope. The experimental results are compared with the corresponding theoretical ones and useful conclusions have been drawn from both the results accordingly.