Design and Validation of a Low-Cost Educational Impact Hammer for Modal Analysis Studies

Resumo

Modal analysis is a technique used to identify the dynamic properties of structures, such as natural frequencies, vibration modes and damping. This analysis is essential to predict structural behavior under different excitation conditions and to ensure the integrity and safety of projects. Among the instruments that perform modal tests, the impact hammer is generally used, however the commercial models available on the market are expensive, which makes them difficult for educational institutions with limited budget to access. Thus, this work developed an impact hammer designed to measure the excitation impact force in small to medium-sized structures which will also perform modal analysis. The objective was to create an economically viable and more accessible alternative when compared to the equipment available on the market. Furthermore, the project serves as a didactic kit, facilitating the teaching and understanding of the principles related to structural vibration. In order to perform the appropriate measurements, the hammer has a load cell, seismic mass and analog electronics, this allows the measurement of impact forces and perform the frequency response analysis of a body. Additionally, this instrument was developed through machining, which allowed the creation of an internal cavity to house the components. The handle was produced using stainless stell, designed to internally incorporate the electronic circuits for the system to operate. Calibration was performed using Bump Test and based on Newton's Second Law, using the previously determined seismic mass and the acceleration of gravity as a reference. To this end, a device was built that standardizes the acceleration applied to the system, allowing repetitions and controlled impacts. Moreover, in each test, the electrical voltage generated by the compression of the piezoelectric cell was analyzed. The final validation of the system was an experiment in which a clamped steel bar was subjected to impact excitation. The results achieved were satisfactory when compared with the theoretical model of the bar and with data obtained from a commercial instrument, ensuring accuracy with an error of 5%.