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With the reason of its high strength, good corrosion resistance and high heat resistance, titanium alloy has been widely used in aeronautical field, especially in aero-engine design. Because of the characteristics of cold state and flexibility, belt grinding is one of the effective titanium alloy finishing. However, the variation of residual stress with grinding parameters in the belt grinding process are not clear, which greatly limits the further application of this method. In this paper, based on the knowledge of molecular system dynamics, a molecular system dynamics model of residual stress on the surface of abrasive belt grinding of titanium alloy is established. Based on the corresponding intermolecular potential function of titanium alloy material, a linear regression equation is established, and the expression of residual stress at molecular level on the surface of belt ground titanium alloy was obtained. The model is simulated with MATLAB, and the results are in good agreement with the intermolecular potential model. Through relevant experiments, the experimental results are compared with the simulation results of titanium alloy molecular system, the error is analyzed and the conclusion is given. When the grinding linear velocity is 8-24 m/s and the feed velocity is 20-60 m/ min, the residual stress of TC17 alloy belt grinding is - 169 to – 254 MPa, and the model prediction error is within 20%.

MnO is a promising anode material for LIBs due to its low cost and high theoretical capacity, but large volume changes and low conductivity limit its application. To improve its conductivity and electron transport rate, we fabricated mesoporous MnO/C hollow microtube through a hydrodynamic force-induced rapid assembly in T-type microchannel reactor followed with a sintering process. The as-synthesized mesoporous MnO/C hollow microtube is consist of MnO nanograins with abundant porous reaction sites embedding uniformly on carbon layers to form a hollow tubular-like structure. When used this mesoporous MnO/C hollow microtube as an anode material of LIBs, it can deliver a high reversible capacity of 845 mAh·g−1 after 100 cycles at 1.5 A g−1 and a capacity of 699 mAh·g−1 at 3.75 A g−1, exhibiting good rate capability and cycle stability. The temperature-dependence electrochemical impedance spectra showed that the mesoporous hollow microtube structure can decrease the barrier energy for jumping through the SEI film, the intercalation reaction and the diffusion of Li+ in the bulk of the solid. The improved performances can be attributed to the unique mesoporous hollow-tubular structure, which enhances the structural stability, improves the electrical conductivity and fasten electrode reaction kinetics.

Fatigue cracks at rib-to-crossbeam welded joints in orthotropic steel decks (OSDs) accelerate degradation of steel bridges. This research aims to investigate fatigue cracking characteristics of rib-to-crossbeam welded joints, and assess the fatigue strength of the welded joints through fatigue testing and finite element analysis. Nine large-scale specimens were tested under static and fatigue loading to explore the failure mode, fatigue life, and failure process. The fatigue test results were compared with the fatigue strength values recommended in different design specifications. Based on the hot spot stress and notch stress approaches, S N curves for rib-to-crossbeam welded joints were derived and compared with the existing fatigue test data. The results indicate that fatigue cracks that initiate from the weld end at the weld toe controls the fatigue resistance of the rib-to-crossbeam welded joints. A statistical analysis was performed to study the probability distribution of the fatigue strength.

We have investigated the debonding failure of the through-silicon via (TSV)–Cu/Si interface during annealing treatment at 425 °C. The interface microstructure was characterized by two parameters: the TSV–Cu/Si interface roughness and the Cu seed layer grain size. Scanning electron microscopy observation of the cross-section of the TSV–Cu/Si interface was performed to analyze the effect of the interface microstructure on its microcrack failure. In addition, qualitative numerical simulations were performed to investigate the effect of the TSV–Cu/Si interface roughness and Cu seed layer grain size on the overall response of the TSV–Cu/Si interface crack. The experimental results indicate that most of the TSV interfacial cracks propagate along the Cu seed layer after annealing, and the crack length of the TSV–Cu/Si interface increases with increasing interface roughness and Cu seed layer grain size. The numerical simulation is constructed to reveal the interfacial crack mechanism, and the results suggest that the stress concentration in the Cu seed layer which influence by interface roughness and Cu grains size is the main driving force for interfacial cracking. Based on the experimental and simulation results, guidelines for controlling the TSV-Cu/Si interfacial cracking from the perspective of the TSV manufacturing process are proposed.

Degradation characteristics and mechanisms of AlGaN/GaN high electron mobility transistors (HEMTs) were investigated under swift heavy-ion irradiation. AlGaN/GaN HEMTs were exposed to 800 MeV Bi ions with fluence up to 5.28 × 10 10 ions/cm 2 . Post-irradiation measurement shows that the saturation drain current reduced by 15%, the maximum transconductance decreased by more than 27%, and both the positive and negative gate characteristics degraded dramatically. By the off-state examination using the Photo Emission Microscopy (PEM), electroluminescence hot spots were found in the gate areas, which indicates new leakage passages produced by heavy-ion bombardment. Micro cross sections were prepared at hot spot areas by dual-beam focused ion beam (FIB) and examined using transmission electron microscope (TEM). The presence of latent tracks throughout the whole hetero-junction area was confirmed. Latent tracks, which related to the high density ionizing energy-loss, play a role of new leakage paths and account for the increment of gate leakage. Moreover, nonionizing energy-loss induced defects decrease the charge density in the two-dimensional electron gas (2DEG) and reduce the carrier mobility, leading to the degradation of device output performances.

A new broadband circularly polarized dielectric resonator antenna (CP DRA) with parasitic elements is presented in this article. The DRA is consisted of a square DR with a pair of rectangular cut corners, two parasitic half-ring DRs, and a square ground plane. A stepped microstrip line is used as the feeding structure by cross-slot aperture coupled way for better impedance matching. Different from the traditional rectangular parasitic metallic plates, a pair of half-ring DRs are introduced as parasitic element to generate additional AR passband in this article. An optimized antenna model is fabricated and tested for verifying the design concept. The tested results indicate the presented antenna features a wide 10-dB impedance bandwidth (IBW) of 52.2% (3.06 GHz, 2.30–3.82 GHz), and a wide 3-dB axial ratio bandwidth (ARBW) of 46.8% (3.08 GHz, 2.36–3.80 GHz).

Displacement damage induced degradations in four-junction solar cells are investigated by electron irradiation and TCAD simulation. It shows that In0.3Ga0.7As cell is the key sub cell to affect the radiation tolerance of four-junction solar cell. Although irradiation will introduce relatively uniform displacement damage in each sub cell of four-junction solar cell, the In0.3Ga0.7As cell show the most significant degradation under the same radiation damage conditions. The radiation harness of the four-junction solar cell can be promoted by increase the short circuit current of In0.3Ga0.7As cell before irradiation, which is verified by the TCAD simulations. The relationship between electrical characteristics degradations and the displacement damage dose is established for four-junction solar cells. Then, the equivalent displacement damage dose method has been used to predict the on-orbit degradation of four-junction solar cells. The degradations of the four-junction solar cells on typical geosynchronous earth orbit are calculated by combining Monte Carlo simulations and ground irradiation test data.