As one of the most intuitive methods for characterizing damage evolution states, time-frequency analysis can be employed to describe the variation law of damage patterns in the time-frequency domain, thereby clarifying the damage evolution state at different stages. However, the damage evolution of composite materials is a very complex nonlinear multi-excitation coupling process, which leads to the existence of cross terms in time-frequency analysis, which seriously interferes with the time-frequency characteristic information transmitted by various damage modes. To solve the above problems, this paper proposes a time-frequency analysis method based on improved adaptive variational mode decomposition (AVMD) and Wigner-Ville distribution for cross-term suppression of multi-component signals. The method uses short-time Fourier transform in advance to estimate the type of damage modes and the center spectrum of acoustic emission signals. The optimal penalty factor is selected by evaluating the correlation between the VMD modal component spectrum and the original signal center spectrum, and then the Wigner-Ville distribution of various damage modes is calculated. The experimental results show that the damage pattern recognition results of this method are consistent with those of SEM and can effectively suppress the cross terms interference of Wigner-Ville distribution in various damage modes. Based on the time-frequency analysis results of damage modes and the corresponding energy characteristics, the AE signal characteristics and damage mechanism of wind turbine blade main spar materials with different defects in different damage evolution stages were defined.
This study investigates the dynamic response and failure mechanisms of graphene reinforced polylactic acid (PLA) composites fabricated via fused filament fabrication (FFF) under low-velocity impact (LVI) loading. The influence of graphene concentrations, ranging from 0.4 to 1.6 wt
Measurement of the unsteady lift acting on test structures inside wind or water tunnels is challenging because flexible test structure dynamics induce errors in base-embedded force transducers. Force reconstruction techniques attempt to mitigate such errors by inversely estimating the applied force, oftentimes by way of modal filtering of structural response measurements. A previous work by Jones and Vlajic utilized dynamic fluid non-dimensional scaling as optimization criteria to calculate modal filters for the purpose of identifying the unsteady lift acting on flexible test structures inside wind or water tunnels directly from base-embedded force transducers. In the present work, we extend the previous methodology to determine unsteady lift spatial force distributions. In the proposed technique, forces within the spatial distribution are assumed to be some fraction of the total force on the structure and to be spatially uncorrelated. Additionally, the distribution is assumed to not vary significantly over the tested range of water tunnel flow speeds. The unsteady lift on the flexible structure is first estimated by way of non-dimensional scaling optimization. Results are then used to supplement an optimization problem in which the error is minimized between modal forces estimated via acceleration response measurements and those estimated via the unsteady lift. Numerical validation is provided as proof-of-concept, while experimental results are also provided to validate the mathematical framework and test assumptions.
Rubber vibration damping is among the most widely used classical vibration mitigation structures. In this study, based on the actual service conditions of rubber vibration dampers, a dedicated axial high-cycle fatigue test fixture was developed for rubber vibration damper structures. High-cycle fatigue tests and thermal effect studies were conducted on specimens subjected to accelerated aging under temperature and irradiation conditions, as well as on specimens with 4 years of service exposure. The microscopic fatigue failure laws of rubber vibration damping structures were elucidated, and the fatigue life under various operating conditions was obtained. The results demonstrate that the fatigue failure life of rubber vibration damping structures after temperature and irradiation acceleration is superior to that of new dampers. For dampers with 4 years of service, the remaining average fatigue failure life is more than 1.5 times higher than that of new dampers from the same batch. Moreover, the fatigue heating temperatures of rubber damper structures before critical failure do not significantly affect on the fatigue life of the damping structures.
Abnormal drill string vibrations frequently lead to premature failure, particularly in air drilling operations where the absence of drilling fluid lubrication exacerbates vibrational severity. To address this challenge, this paper proposes an Air Drilling Shock Absorber (ADSA) and systematically evaluates its mitigating effects on drill string dynamics. Firstly, the structural parameters of the ADSA's elastomeric components were optimized using finite element analysis (FEA), and the structural integrity was validated through physical pressure testing. Subsequently, a comprehensive drill string dynamic model was established, incorporating the tool's working mechanism and actual downhole operating conditions. The axial displacement, velocity, and acceleration of the drill string were then obtained via numerical solutions. A comparative analysis reveals that the integration of the ADSA significantly attenuates the vibration displacement, velocity, and acceleration across various sections of the drill string. Finally, field validation using vibration data from actual drilling operations demonstrated that the ADSA effectively suppresses drill string vibrations, thereby offering robust protection for the drill string and Bottom Hole Assembly (BHA).
