Search Results

Image-based methods in vibration measurements typically require the use of complex high-speed camera systems. By using the recently introduced Spectral Optical Flow Imaging method, full-field high-frequency vibration data can be measured using a cost-effective still-frame camera. Using a single camera, only the motion perpendicular to the optical axis can typically be identified. Depth information, lost in the 2D imaging process, can be obtained by employing multi-camera imaging systems. Alternatively, the recently introduced frequency domain triangulation method offers a way of measuring full-field 3D deflection shapes using a single, moving camera. This research presents the required theoretical background to combine the Spectral Optical Flow Imaging and frequency-domain triangulation methods in an experimental modal analysis experiment using a single, moving still-frame camera.

Fused filament fabrication (FFF) 3D printing technology, one of the most accessible additive manufacturing technologies, can be used to create sensors based on different sensing principles, e.g.: capacitance, inductance, piezoelectricity, piezoresistivity. Piezoresistivity (strain-dependent electrical resistivity) has been predominantly used for the creation of static/quasistatic 3d printed sensors with relatively low sensitivity. This study researches the possibilities of a single-process 3d printing of a piezoresistive accelerometer. Initially, the methods for the axial and cross-axial identification of the piezoresistive properties are discussed. It is shown that the sensitivity is highly dependent on the printing parameters, especially the printing track orientation vs the mechanical load orientation. The research on the sensitivity of a 3D printed piezoresistive structure is extended with an inertial mass-based accelerometer design.

In electric motors the working torque results from the magnetic forces (due to the magnetic field). The magnetic forces are also a direct source of structural excitation; further, the magnetic field is an indirect source of structural excitation in the form of magnetostriction. In the last decade other sources of structural excitation (e.g. mechanical imbalance, natural dynamics of the electric motor) have been widely researched and are well understood. On the other hand, the excitation due to the magnetic forces and magnetostriction is gaining interest in the last period; especially in the field of auto-mobility. Due to the broadband properties of the magnetic field (e.g. Pulse-Width-Modulation(PWM), multi-harmonic excitation), the direct structural excitation in the form of magnetic forces is also broadband.

Car components are exposed to the random/harmonic/impact excitation which can result in component failure due to vibration fatigue. The stress and strain loads do depend on local stress concentration effects and also on the global structural dynamics properties. Standardized fatigue testing is long-lasting, while the dynamic fatigue testing can be much faster; however, the dynamical changes due to fatigue are usually not taken into account and therefore the identified fatigue and structural parameters can be biased. In detail: damage accumulation results in structural changes (stiffness, damping) which are hard to measure in real time; further, structural changes change the dynamics of the loaded system and without taking this changes into account the fatigue load in the stress concentration zone can change significantly (even if the excitation remains the same). This research presents a new approach for accelerated vibration testing of real structures.