Title: Experimental Research on Vibratory Properties of an Engine Hood
text: A method and measurement system are developed for the experimental determination of vibratory properties of complex structures and applied to the determination of the engine hood for the passenger car “ZASTAVA”. Using a mechanical transfer impedance, the vibratory properties and damping factors are determined. The driving force at one point and the velocities at different points of the engine hood are measured. The vibratory properties of the engine hood have been analyzed and compared with regard to the stages of production completion: (1) engine hood without reinforcements, paint, and anti-rumble material; (2) engine hood without paint and anti-rumble material; and (3) engine hood complete. In all cases the engine hood was mounted on the nude car body for testing. Three levels of constant sinusoidal vibration force were applied in the middle point of the engine hood. The results are given in the form of velocity-frequency curves (velocity spectrum) for different measured points, force levels and different assembly stages in production. The hood reinforcements resulted in decreased output velocity levels of a factor between 2.0 and 2.5. On the other hand, the increase of the stiffness of the engine hood structure shifts the resonance frequencies and extends the peak outputs toward lower frequencies. A method for determination of the damping factor and relative damping are presented. By applying the anti-rumble material noise levels decreased by 1.0 to 1.5 dB(A). The output vibration levels decreased as well.