[en] Thermoelastic damping (TED) is considered to be the main internal energy dissipation mechanism in microresonators, the study of which has become increasingly significant in the design of microresonators with high quality factor. In this paper, the bilayered cantilever, fixed-fixed and fully clamped rectangular microplate resonators are taken as the research object, and then three theoretical models of thermoelastic damping with three-dimensional heat conduction are built. The analysis on convergence items of the present three dimensional models with different combinations of materials are carried out, and the influence of material plating on TED in Si microplate resonators is also analyzed. The analysis on the effects of the geometry size and boundary conditions on thermoelastic damping of microresonators at the first-order natural frequency are both carried out. Moreover, in order to verify the validation and accuracy of the present three-dimensional (3-D) models, the previous one-dimensional (1-D) models and the FEM models built in this paper are used to compare with the present models. Finally, the validation and accuracy of the present three-dimensional models are confirmed.

[en] We have found that two 'asymptotic' aspects α and β of an asymptotic iteration method for the Dirac equation satisfy nonlinear Riccati equations simultaneously and are reciprocal to each other. By these two properties, we have an insight into this method and reveal why this method can give solutions to the Dirac equation. Furthermore, using the new iteration termination condition expressed by equation (15), instead of solving the differential equations directly, we have found exact eigenvalues as well as exact wavefunctions of the Dirac equation with two dimensional Coulomb potential

[en] Highlights: • LiBF_2SO_4 was investigated as a novel salt for advanced lithium-ion batteries. • LiBF_2SO_4-EC/DEC shows excellent film-forming characteristic on the surface of LiMn_2O_4. • LiBF_2SO_4-based electrolyte has good compatibility with LiMn_2O_4 cathode. - Abstract: Lithium difluoro(sulfato)borate (LiBF_2SO_4) is investigated as a lithium salt for non-aqueous electrolytes for LiMn_2O_4 cathode in lithium-ion batteries. Inductively coupled plasma-atomic emission spectrometry analysis is used to analyze the Mn dissolution. Scanning electron microscopy and AC impedance measurements analysis are used to analyze the formation of the surface film on the surface of LiMn_2O_4 cathode. These results demonstrate that LiBF_2SO_4-based electrolyte favourably facilitates the formation of an effective and conductive interface film on the cathode surface to improve the stabilization of cathode/electrolyte interface. Besides, LiMn_2O_4 cells using LiBF_2SO_4-based electrolyte exerts several advantages, such as stable cycling performance, low cell impedance, low polarization resistance, and good rate performance. It suggests that LiBF_2SO_4-based electrolyte has good compatibility with LiMn_2O_4 cathode, and LiBF_2SO_4 would be a very promising lithium salt for LiMn_2O_4 cathode in lithium-ion batteries

[en] Highlights: • A novel salt of LiBSO_4F_2 is used as an functional electrolyte additive. • Electrolyte with LiBSO_4F_2 has high stability against oxidation decomposition (∼5.6 V). • LiBSO_4F_2 additive could decrease the interfacial impedance of LiNi_0_._5Mn_1_._5O_4/Li cells. • LiBSO_4F_2 additive could improve electrochemical performance of LiNi_0_._5Mn_1_._5O_4/Li cells. - Abstract: To seek a promising candidate for 5 V electrolytes, fluorine-free lithium bis(oxalato) borat (LiBOB) is chosen as the lithium salt, and lithium difluoro(sulfato) borate (LiBSO_4F_2) is investigated as an additive for the stabilization of a high-voltage LiNi_0_._5Mn_1_._5O_4 cathode. Cyclic voltammetry test, AC impedance measurement and scanning electron microscopy (SEM) analysis are used to examine the electrochemical stability and the compatibility between electrolytes and LiNi_0_._5Mn_1_._5O_4 cathode. It is found that the addition of 0.1 M LiBF_2SO_4 to 0.7 M LiBOB-based electrolyte could significantly decrease the interfacial impedance of LiNi_0_._5Mn_1_._5O_4/Li cells, due to the fact that LiBSO_4F_2 is involved in the formation of protective film on cathode surface, as well as the prior oxidation reactions of LiBOB. Moreover, LiBSO_4F_2 additive could obviously improve both of the capacity retention and the rate performance of lithium-ion cells. These results demonstrate that using blend salts can combine the advantages of LiBOB and LiBSO_4F_2 to maximize the electrochemical performances of lithium-ion cells

[en] A novel hybrid process that integrates end electric discharge (ED) milling and mechanical grinding is proposed. The process is able to effectively machine a large surface area on SiC ceramic with good surface quality and fine working environmental practice. The polarity, pulse on-time, and peak current are varied to explore their effects on the surface integrity, such as surface morphology, surface roughness, micro-cracks, and composition on the machined surface. The results show that positive tool polarity, short pulse on-time, and low peak current cause a fine surface finish. During the hybrid machining of SiC ceramic, the material is mainly removed by end ED milling at rough machining mode, whereas it is mainly removed by mechanical grinding at finish machining mode. Moreover, the material from the tool can transfer to the workpiece, and a combination reaction takes place during machining.

[en] The difference between the design adaptabilities of shield cutter head system has a strong impact on the tunnelling efficiency. How to study and evaluate its design adaptability is an urgent problem to be solved. In this paper, based on the membership matching degree of adaptability quality of shield cutter head system between the existing design and ideal design, and taking the matching degree as the initial data of the evaluation model, a design adaptability analysis model and evaluation method based on entropy weight improved TOPSIS are proposed. Taking the existing design of shield cutter head system as an example, the adaptability in subway construction are analysed and evaluated. The 9 adaptability indexes are ranked, and the conclusion is drawn that the adaptability of 17 design tasks of the cutter head system are general, which verifies the practicability and credibility of the method. (paper)

[en] Nine specimens were tested to investigate the local bearing capacity of steel beams with corrugated webs. Then, the influence of different load distribution widths on local bearing capacity was studied. Results showed that the failure modes of the specimens were web yielding and changed from brittle failure to plastic failure at increased distribution width. The ultimate bearing capacities were higher than those of steel beams with plate webs. Meanwhile, the loading course, ultimate load and failure modes were closely simulated through the finite element method, and parameter analysis was performed, the result of which verified the decreased capacity of the sparse waveforms. The design expression of the local bearing capacity under different load distribution widths were obtained on the basis of these results and applied to crane beams with corrugated webs. The calculated results compared with finite element analysis and experimental results suggested the correctness and reliability of the design expression.

[en] Thermoelastic damping (TED) is considered to be the main internal energy dissipation mechanism in microresonators, the study of which has become increasingly significant in the design of microresonators with high quality factor. In this paper, the bilayered cantilever, fixed-fixed and fully clamped rectangular microplate resonators are taken as the research object, and then three theoretical models of thermoelastic damping with three-dimensional heat conduction are built. The analysis on convergence items of the present three-dimensional models with different combinations of materials are carried out, and the influence of material plating on TED in Si microplate resonators is also analyzed. The analysis on the effects of the geometry size and boundary conditions on thermoelastic damping of microresonators at the first-order natural frequency are both carried out. Moreover, in order to verify the validation and accuracy of the present three-dimensional (3-D) models, the previous one-dimensional (1-D) models and the FEM models built in this paper are used to compare with the present models. Finally, the validation and accuracy of the present three-dimensional models are confirmed.

[en] In the microscopic view, the contact between two solid surfaces is reckoned to be the contact among asperities indeed. These asperities loaded which contact with each other are to experience three stages of deformation in succession: elastic deformation, elastic–plastic deformation, and plastic deformation, not the direct transition from elastic deformation to plastic deformation. In addition, these asperities should be distributed on the three-dimensional surface topography, and the corresponding fractal dimension is $2<D<3$. In this study, firstly, based on the fractal theory and Hertz contact theory, the loading fractal model of rough dry-friction joint surfaces is established in consideration of elastic–plastic deformation of asperities and three-dimensional surface topography. Secondly, two important fractal parameters, fractal dimension D and fractal roughness G, can be calculated according to sampled surface topography of 45 steel and power spectrum density function method. Then, the effects of friction factor $\mathrm{\mu <!--\; ??\; -->}$, fractal dimension D, and fractal roughness G on the loading fractal model are analyzed by numerical simulation. Finally, the present model is compared with experimental data and other models, which indicates that their trends are the same. The elastic–plastic loading modeling provides a certain theoretical reference for the accurate solution of contact among rough surfaces.

[en] This work elucidated the effects of damage and self-healing on the frequency-dependent electrical response of strain-hardening cementitious materials. Electrical impedance spectroscopy was conducted before material cracking, during single crack opening, sequential formation of multiple microcracks, and subsequent self-healing of the microcracks. The results revealed that the material complex impedance was strongly influenced by crack opening and crack number; both changed during mechanical straining as well as the self-healing process. A new equivalent circuit model was formulated for predicting the frequency-dependent electrical response of the material during damage evolution and self-healing process. Analyzing the changes of model parameters revealed the mechanisms that contribute to the frequency-dependent electromechanical response of the material. This study generated new experimental data and analytical model coupling the electrical response with damage level in cementitious materials. The new understandings are critical for the next step of realizing damage sensing in strain-hardening cementitious materials through frequency-dependent AC measurements.