Practical Calibration Techniques for the Modal Impact Hammer

Abstract

Modal impact hammer comprised of a force transducer, a hammer body and different impact tips, is widely used in structural dynamic testing. Users might usually overlook the sensitivity of the impact hammer since it has no influence on the estimation of modal frequency, damping, and mode shape in a Multiple Reference Impact Test (MRIT). However, for the reason of accurate measurement and analysis for estimating the modal scaling factor or measuring the inertial mass of the structure, the calibration process has to be performed in advance. For the majority of off-the-shelf impact hammers, the force transducer cannot be detached. Moreover, the sensitivity of the integrated force transducer is not identical with the hammer because the force is transferred from the sensor to the structure via the impact tip. Therefore, the calibration method for common force transducers is not suitable for the impact hammer. In this paper, on the basis of drop calibration, two practical methods using an accelerometer and a load cell are presented respectively to calibrate the impact hammer and findings are compared with each other. The influence of different impact tips to the sensitivity of the hammer is also discussed.