Thrust testing units with a piezoelectric dynamometer have unique traits such as excessive stiffness, tremendous measurement accuracy, dynamic performance and no hysteresis. These are widely used in the applications requiring force/thrust measurements in the aerospace industry and high‐end tool condition monitoring. The performance of these units is necessary to be evaluated. In this study, an improved layout of six‐degree of freedom force/thrust measurement stand is proposed and analysed theoretically and experimentally. The measurement stand is a structural component to measure six components of force, such as axial force/thrust (FX, FY, and FZ ) and other components (MX, MY, and MZ ). Test stand consists of seven piezoelectric sensors in two sections. The front part consists of four piezoelectric force sensors, while the rear part consists of three sensors. The rear section is hexagonal, with three sensors mounted at 120°. The measurement stand can measure the principal force/thrust up to 50,000 N. A mathematical model is derived for every sensor against forces in all directions. To calibrate the stand, a calibration platform is designed and fabricated. The calibration platform can generate a range of forces/moments. Calibration experiments verifies that the measurement stand is fairly functional to measure variety of forces/moments with high repeatability.
A particle impact damper (PID) dissipates the vibration energy of a structure through impacts within the damper. The PID is not commonly used in practice mainly because of its low damping-to-mass ratio and the difficulty in achieving its optimal design due to its nonlinear characteristics. In contrast, a Coulomb friction damper (FD) can offer a higher damping force-to-mass ratio than other dampers, but it is also difficult to be controlled precisely due to its nonlinear characteristics and excessive frequency sensitivity regarding the resonant frequency. This paper examines a hybrid damper by combining a particle impact damper and a Coulomb friction damper (PID + FD) theoretically and experimentally. A theoretical model of the proposed damper is developed and tested numerically on a single-degree-of-freedom (SDOF) structure. The predicted results are validated by experimental tests on a prototype of the proposed damper. The damping force provided by the FD in the prototype can be varied by adjusting the normal force applied through a compression spring, while the vibration energy dissipation by the PID can be varied by changing the cavity size of the PID. A parametric analysis of the proposed hybrid damper has been performed. The proposed hybrid damper can reduce the maximum vibration amplitude of the SDOF primary structure by 66% and 43% compared with using the FD and PID only. The proposed damper is found to be effective over a wide range of excitation frequencies. Furthermore, the proposed hybrid damper achieves a similar vibration suppression performance to the traditional tuned mass damper (TMD) of a similar mass ratio. The proposed damper does not require an optimally tuned natural frequency and damping, unlike the TMD, and therefore it does not have the detuning problem associated with the TMD. In addition, the performance of the proposed damper is tested and compared with the TMD for random earthquake excitation data. Consequently, the proposed hybrid damper may be a simpler and better alternative to the TMD in passive vibration control applications.
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