RESUMO
Sinusoidal shock waveforms are the classical type of waveforms generated in Drop Test Machines (DTMs) using Rubber Wave Generators (RWGs). For different specifications of pulse, different RWGs are used, leading to the laborious work of replacing RWGs in DTMs. In this study, a novel technique is developed to predict a shock pulse of variable height and time using a Hybrid Wave Generator (HWG) that yields variable stiffness. This variable stiffness is a combination of the fixed stiffness of rubber and the variable stiffness of magnet. A mathematical nonlinear model has developed, consisting of a polynomial model of RWG and an integral approach of magnetic force. The designed HWG is capable enough to produce a strong magnetic force as a result of a high magnetic field generated in the solenoid. This magnetic force combines with rubber to give a variable stiffness effect. This way, a semi-active control of the stiffness and pulse shape is achieved. Two sets of HWGs are tested to study the control over the shock pulse. An average hybrid stiffness from 32 to 74 kN/m is observed by varying voltage from 0 to 1000 VDC, resulting in a change of height of pulse from 18 to 56 g (net change 38 g) and a change of shock pulse width from 17 to 12 ms (net change 5 ms). From experimental results, it is concluded that the developed technique gives satisfactory results for the control/prediction of variable shape shock pulse.
