Thoughts on Automatic Impulse Hammer Parameters and Sensor Fixation Methods

The majority of data acquisition in experimental structure dynamics are conducted using impulse excitation and acceleration sensors. As the shape of the impulse in time domain is the crucial basis for the frequency content calculated from the impulse, mechanical parameters of the automatic modal impulse hammer (AMimpact) are discussed that have an influence on the impulse function. Using minimal models, the individual effects of the parameters are theoretically discussed and shown in experiments. Mounting the sensors to the structure is a critical step towards achieving good measurement quality. This investigation presents an overview and compares several, feasible methods for fixing acceleration sensors to metal (aluminum) structures. The methods are discussed regarding their effort, their positional precision, and their repeatability. The various methods are discussed in terms of their positional precision and their repeatability. The experiments are conducted and analyzed on an academic aluminum test structure and the automatic modal hammer (AMimpact). One difficulty is the lack of any ground truth, for which reason two sensors are stacked together to compare frequency response functions. These FRFs are obtained in two directions to enable the sensor fixation to be loaded in normal and tangential direction. The conclusion of the paper states that the fixing methods used for acceleration sensors are not critical in the normal direction but can have a non-negligible influence on measurements in the tangential direction. This effect should therefore be considered at an early stage of a measurement campaign.