Experimental and numerical investigation of the effect of microstructural changes on the vibrational characteristics of ck35 steel

This study aims to identify the microstructural changes of metal by measuring its natural frequency and damping loss factor. For this purpose, six CK35 steel specimens with ferritic-pearlitic structure were prepared and then, four specimens were spheroidized to significantly change microstructures. Subsequently, the modal testing was applied to determine the vibrational characteristics of specimens with ferrite-pearlite and spheroidized structures, which were identical in terms of size and weight. Experimental results indicated that the dispersion of spheroidized carbides in the ferritic matrix could increase natural frequencies and damping loss factors, such that changing the microstructure of specimens increased the natural frequency and damping loss factor of the first vibration mode by 0.4 (from 3732 to 3747 Hz) and 15%, respectively. Finally, a microstructure-based finite element model was developed to interpret experimental results. The representative volume element (RVE) was modeled using image processing and writing scripts in ABAQUS/CAE 2016. The statistical analysis of stresses calculated by finite element analysis confirmed the results obtained by experimental tests. The numerical results showed that changing microstructures led to considerable changes in stress statistical dispersion, although the mean stress value did not change. Ultimately, the approximate formula of stress-damping could explain significant changes in the damping loss factor.

Dynamic Response Analysis of a Thin Plate with Partially Constrained Layer Damping Optimization under Moving Loads for Various Boundary Conditions

In this paper, the vibration analysis of a partially constrained layer damping plate subjected to moving loads is investigated. In addition, the first four order damping loss factor of the system is optimized with the location of partially constrained layer damping as a design variable. The equations of motion of a partially constrained layer damping plate are derived through the Lagrange equation based on first order shear deformation theory (FSDT). Next, using an extended Rayleigh–Ritz solution together with the penalty method expresses the unknown displacement terms, and the differential quadrature method is proposed to obtain the dynamic response of the system in the time domain. A multi-population genetic algorithm (MPGA) is employed to deal with the optimization of the damping loss factor of a partially constrained layer damping plate. To ensure the accuracy of the method presented in this study, the numerical results are comprehensively verified by experiments and open literature. The optimization results show that the damping loss factor increases when the position of the patch is close to the constraint boundary, and the best strategy is to optimize the low order damping loss factor of the system under moving loads. It is believed that the research results are of interest to engineering science.

Damping Determination by Half-Power Bandwidth Method for a Slightly Damped Rectangular Steel Plate in the Mid-Frequency Range

This paper presents a novel methodology for measuring the Damping Loss Factor (DLF) of a slightly damped plate in the mid-frequency range (400-1000 Hz) by the Half Power Bandwidth Method (HPBM). A steel flat plate of 650 x 550 x 2 mm was considered as the test case, which was excited by both a shaker and an impact hammer to quantify the effect of the excitation type for slightly damped plate. Since the HPBM is based on extracting the damping data from the modal resonance peaks, working with the correct Frequency Response Functions (FRF) was found to be a crucial factor. Therefore, the effects of coherence and resolution of the sampling frequency were examined in detail in the measurements. The obtained DLF results were statistically analysed and then applied in SEA simulations. Comparison of the simulation and experimental results showed that the method of extracting the DLF data from the measurements can have as much as 10 dB influence on the simulation results. The best results, with only 2 dB difference between measurement and simulation, were obtained when the statistical expected value of the data was used as the input in the SEA simulations.

Vibrational Energy Flow Model for a High Damping Beam with Constant Axial Force

The energy flow analysis (EFA) method is developed to predict the energy density of a high damping beam with constant axial force in the high-frequency range. The energy density and intensity of the beam are associated with high structural damping loss factor and axial force and introduced to derive the energy transmission equation. For high damping situation, the energy loss equation is derived by considering the relationship between potential energy and total energy. Then, the energy density governing equation is obtained. Finally, the feasibility of the EFA approach is validated by comparing the EFA results with the modal solutions for various frequencies and structural damping loss factors. The effects of structural damping loss factor and axial force on the energy density distribution are also discussed in detail.

Vibration Damping Measurement on Car Windshields

Knowledge of the damping properties of a windshield is a fundamental element of the acoustical characterization of a car. The measuring method of damping for a windshield is presented in the paper. The damping loss factor – as a basic measure of mechanical damping – was determined experimentally by two means: the reverberation time from impact hammer testing as well as the modal behavior from 3D laser scanning vibrometer measurements. The results proved that the modal shapes have a fundamental effect on the measured damping values.