China
Africa
Explore chapters and articles related to this topic
Viscoelastic composite materials
Published in Roderic S. Lakes, Viscoelastic Solids, 2017
Damping in metal-matrix composites can arise due to damping in one or both of the phases. Use of a high-loss phase such as magnesium can give rise to a high-loss composite. In some particulate composites, an excess of damping is attributed to high concentrations of dislocations near the metal-ceramic interface [9.7.18]. Damping due to thermoelastic coupling (§8.3) may be important in some metal-matrix composites. Thermoelastic damping in composite materials arises due to the heterogeneity of the thermal and mechanical properties of such materials, leading to heat flow between constituents, hence, mechanical energy dissipation. Such damping is not accounted for in the above treatments (§9.3) via the correspondence principle since the overall actual damping contains a contribution from a coupled-field interaction between the constituents.
Enlarging quality factor in microbeam resonators by topology optimization
Published in Journal of Thermal Stresses, 2019
For the CF microbeam, ESO parameters are chosen as s = 0.8, er =0.01, and the penalty factors are all set to 1. To set an initial guess for the topology optimization of CF microbeam, a vacancy of 4 × 4 void elements is located at both the 1/3 length and the middle length of the microbeam. The optimization process converges after 27 iterations and , as shown in Figures 6 and 7. In the case of CF microbeam, vacancies are optimized close to the clamping end where the gradient of temperature field is the strongest (the temperature contour plot is given in Figure 7). As mentioned above, the thermoelastic damping is due to irreversible heat flux and entropy dissipation caused by the gradient of temperature field. Because the heat flux along the strongest gradient of temperature field is disturbed by topology optimization, irreversible heat flux and entropy dissipation decrease, and therefore we obtain the CF beam resonator with a high quality factor.
Mechanical and thermal couplings in helical strands*
Published in Journal of Thermal Stresses, 2019
Dansong Zhang, Martin Ostoja-Starzewski, Loïc Le Marrec
Next, the temperature effects on the thermoelastic waves are investigated. The main consideration is that, with novel designs of overhead power transmission lines, operating temperatures can reach [40]. The dampings in both the longitudinal waves and the torsional waves increase by a factor of about 1.6 with the temperature increasing from to for our steel strand (Figure 4). But such an increase does not bring a fundamental difference in the damping behavior, as the absolute values of the dampings remain negligible, as shown in Figure 3. Overall, the numerical results show that for the steel strand, the errors of neglecting the thermodynamics and the thermal expansion are very small when compared with the alterations of the celerity brought about by pure tension–torsion coupling. Thermoelastic damping is essentially almost absent for practical applications, and mechanical damping is the dominant source of damping. These results are expected, as they support the use of pure mechanical equations for wave propagations in helical strands for most engineering applications. However, the thermomechanical coupling effect can be large for high temperature applications, or materials with a high coefficient of thermal expansion, as either case leads to large thermoelastic coupling constants.
Thermoelastic damping suppression method of micro-beam resonators with basically constant resonant frequency
Published in Journal of Thermal Stresses, 2022
Rongjun Cheng, Pengcheng Song, Jiaxing Chen, Qiangxian Huang, Liansheng Zhang
Thermoelastic damping is a structural damping mechanism caused by the coupling of thermal and mechanical fields. For a bending thermoelastic structure, the internal part of the bend is forced to compress, and the external part of the bend is forced to stretch. A thermal gradient is generated, resulting in irreversible heat flow inside the structure. The temperature distribution of a micro-beam under lateral vibration is shown in Figure 1. The red area represents the high-temperature area, and the blue part represents the low-temperature area. The internal heat will lead to the production of entropy and the final energy dissipation.