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Free Vibration and Damping Characterization of the Biocomposites
Published in Senthil Muthu Kumar Thiagamani, Md Enamul Hoque, Senthilkumar Krishnasamy, Chandrasekar Muthukumar, Suchart Siengchin, Vibration and Damping Behavior of Biocomposites, 2022
Natural frequency is the frequency in which the body oscillates on its own after the initial disturbance. Generally, all the vibrational systems will have “n” degrees of freedom, which in turn have “n” distinct natural frequencies. On the other hand, damping has a reducing effect on the vibration. In physical systems, damping involves processes that result in the dissipation of stored energy due to oscillation or under cyclic stress. Generally, all composite materials possess high damping capacity due to their viscoelastic phenomena that are associated with the material properties. As a result, the composite materials’ internal damping capacity is determined by (a) composition of matrix and reinforcement, (b) orientation of the reinforcements, and (c) surface treatment of the composite material.
Motor Vibration and Acoustic Noise
Published in Wei Tong, Mechanical Design and Manufacturing of Electric Motors, 2022
As presented by Chung [12.38], damping materials fall into four categories: (a) materials exhibiting high loss modulus but low loss tangent (such as cast iron and shape-memory alloys); (b) materials exhibiting low loss modulus but high loss tangent (such as rubber and other polymers); (c) materials exhibiting low values of both loss tangent and loss modulus; and (d) materials exhibiting high values of both loss tangent and loss modulus (such as graphite networks and cement-matrix composite). High damping materials must have high values of both loss tangent and loss modulus, that is, high damping capacity and high stiffness. For metallic materials, magnesium alloys have comparatively high damping capacity, up to about 3 times that of cast iron and up to about 30 times higher than that of aluminum, and a high strength-to-density ratio. The combination of high damping, good strength, and low mass makes magnesium alloys an excellent choice for vibration damping materials [12.39].
Initial boundary value problem
Published in Adnan Ibrahimbegovic, Naida Ademovicć, Nonlinear Dynamics of Structures Under Extreme Transient Loads, 2019
Adnan Ibrahimbegovic, Naida Ademovicć
During vibration motion (earthquake, etc.) of each and every structure, there would be some energy loss. The latter pertains to damping phenomena in vibrating structures, which in many expositions on the subject have been defined with great uncertainty with no clear recommendations on how to define the damping forces. Damping capacity is defined as the ratio of the energy dissipated in one cycle of oscillation to the maximum amount of energy accumulated in the structure. Material damping and interface damping are the most frequently present damping sources in the structure among many others. The material damping contribution comes from different damage mechanisms and their interaction within the material from which the structure is built. Thus, the damping is dependent upon the type of material, as well as on manufacturing methods (Kareem and Gurley 1996). Taking all this into account and the fact that the material characteristics vary due to material heterogeneities, providing the reliable estimation of material damage on structural damping is perhaps the most reliable path to constructing predictive models. This is illustrated in Part I, for most frequently used structure materials.
Effects of introducing CNTs and GPLs on mechanical, modal, thermal, and water uptake properties of twill basalt fiber-reinforced epoxy matrix composites
Published in The Journal of The Textile Institute, 2023
Farzin Azimpour-Shishevan, Hamit Akbulut, M. A. Mohtadi-Bonab, Bahman Rahmatinejad
Basically, the introduction of nanoscale particles controls the vibrational properties of the composites (Fu et al., 2008). Based on modal test results for both C-F and F-F boundary conditions, addition of carbon-based nanoparticles leads to the increase of NF and decrease of DF except for the composite with 0.5% GPL addition. It should be mentioned that NF and damping ratio were increased by dispersion of 0.5% GPL. On the other hand, low content addition of nanofillers has got better results in increasing of NF. As it is clear, the addition of CNTs and GPLs in the composites considerably enhanced the damping property with the benefit of interfacial friction between the nanoscale particles in the matrix resin (Borbón et al., 2014). The NF depends on the modulus of material and consequently the increase of the stiffness increases the NF and decreases the damping ratio as well. When the critical value of the stiffness at 0.1 wt% of the CNTs and GPLs content was achieved, the decreasing trend was observed for stiffness and NF. These findings documented that agglomeration is formed after the addition of 0.1 wt% content of nanoparticles. This results in increased energy dissipation with the faster rate which leads to increased damping capacity (Bulut et al., 2019; Rajini et al., 2013). Moreover, this may be due to an increase in the ductility of multiscale nanocomposite at higher loadings of nanofillers compared with the net BFE.
Diphenolic acid-modified PAMAM/chlorinated butyl rubber nanocomposites with superior mechanical, damping, and self-healing properties
Published in Science and Technology of Advanced Materials, 2021
Yao Lu, Jincheng Wang, Le Wang, Shiqiang Song
Damping materials have a strong appeal in mechanical engineering applications due to their good vibration and noise reduction capabilities [1,2]. Especially in aerospace, rail transportation and other fields, the demand for high-performance damping materials was growing rapidly and continuously [3,4]. Rubber materials were one of the most commonly used damping materials because of their good mechanical properties and damping capacity [5]. However, there are somedisadvantagessuchasnarrow effective damping area, unstable damping performance, easy fatigue, and aging in practical use, limits their wide application [6,7]. Therefore, it is still important to develop better rubber shock-absorbing materials. The ideal rubber damping material should not only have good damping capacity, but also have good mechanical properties and durability [8,9].
Designing damping capacity in high strength Fe–Mn based alloys by controlling crystal defect configurations
Published in Philosophical Magazine, 2021
Ji Zhang, Yongning Wang, Qiang Luo, Huabei Peng, Yuhua Wen
After quenching from 1373 K, the amount of quenched-in surplus vacancies is very high, but the amount of atoms segregation is negligibly small. During the process of ageing, the quenched-in surplus vacancies will gradually diminish, but the segregation of atoms to stacking faults will gradually increase (Figures 6 and 8). After a short ageing, the reduced pinning due to the decrease in the vacancies is greater than the increased pinning due to the rise in the atom’s segregation. Consequently, the damping capacity was remarkably improved. After a long ageing, the increased pinning becomes greater, and thus the damping capacity declines. This explains why the damping capcity will drop when the ageing time is above 40 min although the number of vacancies will become increasingly lower with further ageing. Obviously, more vacancies will be annihilated when ageing at 423 K than at 373 K for the same time because their mobility is higher. Therefore, the rise in the damping capacity is greater after ageing at 423 K than at 373 K. Similarily, the segregation of solute to stacking faults will be faster and higher when ageing at 423 K than at 373 K. Consequently, the drop in the damping is greater after ageing at 423 K than 373 K (Figure 2b and c).