摘要:
Temperature-dependent material attrition and subsurface lattice damage of single-crystal AlN at various scratching depths/forces are investigated at atomic level using molecular dynamics simulation. An ultimate removal precision of depth down to monolayer of AlN is achieved based on the present temperature-dependent critical conditions. The number of worn atoms, positively influenced by temperature due to the reduction of hardness, increases exponentially with increasing normal force in the plastic domain. Archard-type wear coefficient K values calculated at different temperatures increase linearly with normal force, and the slope is independent of temperature. Independently of load and temperature, a wear coefficient normalized with the tangential contact area, K/Atang, is developed to interpret the removal efficiency of AlN substrate with diamond abrasive.
作者机构:
[Luo, W.; Liu, L.; Li, X. X.; Hu, B. L.; Luo, W; Liu, L; Sun, X. Y.] Univ South China, Sch Nucl Sci & Technol, Hengyang 421001, Peoples R China.;[Han, L. H.; Liu, L.; Liu, L] Univ South China, Sch Mech Engn, Hengyang 421000, Peoples R China.
通讯机构:
[Luo, W; Liu, L ] U;Univ South China, Sch Nucl Sci & Technol, Hengyang 421001, Peoples R China.;Univ South China, Sch Mech Engn, Hengyang 421000, Peoples R China.
摘要:
The management of nuclear wastes has long been a problem that hinders the sustainable and clean utilization of nuclear energy since the advent of nuclear power. These nuclear wastes include minor actinides (MAs: (237)Np, (241)Am, (243)Am, (244)Cm and (245)Cm) and long-lived fission products (LLFPs: (79)Se, (93)Zr, (99)Tc, (107)Pd, (129)I and (135)Cs), and yet are hard to be handled. In this work, we propose a scheme that can transmute almost all the MAs and LLFPs with a lead-cooled fast reactor (LFR). In this scheme, the MAs and the LLFPs are loaded to the fuel assembly and the blanket assembly for transmutation, respectively. In order to study the effect of MAs loading on the operation of the core, the neutron flux distribution, spectra, and the k(eff) are further compared with and without MAs loading. Then the LLFPs composition is optimized and the support ratio is obtained to be 1.22 for (237)Np, 1.63 for (241)Am, 1.27 for (243)Am, 1.32 for (79)Se, 1.53 for (99)Tc, 1.02 for (107)Pd, and 1.12 for (129)I, respectively, indicating that a self-sustained transmutation can be achieved. Accordingly, the transmutation rate of these nuclides was 13.07%/y for (237)Np, 15.18%/y for (241)Am, 13.34%/y for (243)Am, 0.58%/y for (79)Se, 0.92%/y for (99)Tc, 1.17%/y for (107)Pd, 0.56%/y for (129)I. Our results show that a lead-cooled fast reactor can be potentially used to manage nuclear wastes with high levels of long-lived radioactivity.
摘要:
A series of heterostructured materials with variable ratio of 316 powders in 18Ni300 powders were prepared by laser melting deposition (LMD). The microstructural evolution and its influence on tensile features were explored before/after aging treatment or solution-aging treatment. The results indicated that the fraction of g phase was increased gradually with increasing 316SS, and dislocation caused by the deformation could be migrated and annihilated within the region of g phase, second phase strengthening could contribute to excellent elongation for 18Ni300 maraging steel. The elongation of the AF4 sample was 235.2% higher than that of the AF0 sample when a 37.5% reduction in the ultimate tensile strength occurred. In addition, thermal stress could exist in the as-cladded sample, an appropriate heat treatment could release the thermal stress and precipitate nanoscale intermetallic compound. Their synergistic effect could contribute to overcoming the strength-elongation trade-off. A relatively ideal sample, a discontinuous g phase surrounded by a phase, which displayed high strength of 1678.4 MPa with high elongation of 10.9% after solution-aging treatment. Compared with laser cladded 18Ni300 maraging steel, a 41.7% increment in the elongation was obtained at the cost of 11.3% reduction in ultimate tensile strength. & COPY; 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC
摘要:
Purpose
The modeling cost of the gradient-enhanced kriging (GEK) method is prohibitive for high-dimensional problems. This study aims to develop an efficient modeling strategy for the GEK method.
Design/methodology/approach
A two-step tuning strategy is proposed for the construction of the GEK model. First, an auxiliary kriging is built efficiently. Then, the hyperparameter of the kriging model is served as a good initial guess to that of the GEK model, and a local optimal search is further used to explore the search space of hyperparameter to guarantee the accuracy of the GEK model. In the construction of the auxiliary kriging, the maximal information coefficient is adopted to estimate the relative magnitude of the hyperparameter, which is used to transform the high-dimension maximum likelihood estimation problem into a one-dimensional optimization. The tuning problem of the auxiliary kriging becomes independent of the dimension. Therefore, the modeling efficiency can be improved significantly.
Findings
The performance of the proposed method is studied with analytic problems ranging from 10D to 50D and an 18D aerodynamic airfoil example. It is further compared with two efficient GEK modeling methods. The empirical experiments show that the proposed model can significantly improve the modeling efficiency without sacrificing accuracy compared with other efficient modeling methods.
Originality/value
This paper developed an efficient modeling strategy for GEK and demonstrated the effectiveness of the proposed method in modeling high-dimension problems.
期刊:
Particulate Science and Technology,2023年 ISSN:0272-6351
通讯作者:
Deng, R
作者机构:
[Deng, Rong; Lu, Xiaowei; Ye, Tong] Univ South China, Sch Mech Engn, Hengyang, Peoples R China.;[Deng, Rong; Deng, R] Univ South China, Sch Mech Engn, Hengyang 421000, Hunan, Peoples R China.
通讯机构:
[Deng, R ] U;Univ South China, Sch Mech Engn, Hengyang 421000, Hunan, Peoples R China.
关键词:
Fresh concrete;dEM;flowing property;JKR surface energy;rheological test
摘要:
The effect of Johnson-Kendall-Roberts (JKR) surface energy on the flowing property of fresh concrete was numerically studied. The fresh concrete was simplified into coarse aggregate and mortar, both described as the particles. The Hertz-Mindlin with JKR contact model was employed to describe the constitutive relationship of fresh concrete. The contact parameters were calibrated through experiment and numerical simulation of multiple flow tests. The impact of these contact parameters on the residual height (Hr) of fresh concrete after slumping was examined using a slump test. The significance degree of mortar-mortar contact parameters on the Hr was studied using an orthogonal test. The effect of the surface energy (gamma) on the flow index (Bm) and flow time (Tv) of fresh concrete was studied intensively based on the L-box flow and V-funnel tests. The mortar-mortar contact parameters, gamma and rolling friction coefficient (mu r), most significantly impacted the Hr. The mortar-mortar surface energy (gamma m-m) significantly impacted Bm and Tv compared to the aggregate-mortar and aggregate-aggregate surface energies ((gamma a-m) and (gamma a-a), respectively). The effect of gamma a-a, gamma a-m, and gamma m-m on Bm was interconnected. Under appropriate parametric values, the Bm was the most stable, and the workability of fresh concrete was the best. In addition, as gamma increased, Hr and Bm decreased and Tv increased. The flowability of the fresh concrete worsened.
通讯机构:
[Chen, Y ] U;Univ South China, Coll Mech Engn, Hengyang 421101, Peoples R China.
关键词:
FeCrAl coating;numerical simulation;temperature field analysis;laser micromelting;laser process parameters;surface morphology
摘要:
Laser micromelting (LMM) technology allows for the remelting of pre-positioned coatings on the surface of a specimen to form a metallurgical bond with the substrate material, significantly improving the coating's film-base bond. However, the high energy input from the laser modification process can cause severe element diffusion, rendering the coating susceptible to deformation and cracking. This can be mitigated by controlling the laser power, scanning speed, and offset of the LMM process. The temperature and stress fields of the samples in the LMM process were analyzed via finite element simulation. The effects of the LMM process parameters on the coating morphology were analyzed in conjunction with experiments. The results indicated that the laser power significantly affected the morphology of the coating after remelting, and a higher scanning speed was more likely to cause the coating to accumulate stress. Additionally, a smaller offset inhibited crack generation. At a laser power of 30 W, a scanning speed of 1200 mm/min, and a scanning spacing of 0.035 mm, the surface of the coating had no obvious defects and was relatively flat, and the adhesion and corrosion resistance were significantly improved. This study provides valuable guidance for improving the preparation of micron-sized protective coatings on Zr alloy surfaces.
摘要:
Anisotropic plasmonic metasurfaces have attracted broad research interest since they possess novel optical properties superior to natural materials and their tremendous design flexibility. However, the realization of multi-wavelength selective plasmonic metasurfaces that have emerged as promising candidates to uncover multichannel optical devices remains a challenge associated with weak modulation depths and narrow operation bandwidth. Herein, we propose and numerically demonstrate near-infrared multi-wavelength selective passive plasmonic switching (PPS) that encompasses high ON/OFF ratios and strong modulation depths via multiple Fano resonances (FRs) in anisotropic plasmonic metasurfaces. Specifically, the double FRs can be fulfilled and dedicated to establishing tailorable near-infrared dual-wavelength PPS. The multiple FRs mediated by in-plane mirror asymmetries cause the emergence of triple-wavelength PPS, whereas the multiple FRs governed by in-plane rotational asymmetries avail the implementation of the quasi-bound states in the continuum-endowed multi-wavelength PPS with the ability to unfold a tunable broad bandwidth. In addition, the strong polarization effects with in-plane anisotropic properties further validate the existence of the polarization-resolved multi-wavelength PPS. Our results provide an alternative approach to foster the achievement of multifunctional meta-devices in optical communication and information processing.
通讯机构:
[Fang Yu; Haiqing Zhou] K;Key Laboratory of Low-Dimensional Quantum Structures and Quantum Control of Ministry of Education, Key Laboratory for Matter Microstructure and Function of Hunan Province, Department of Physics and Synergetic Innovation Center for Quantum Effects and Applications, Hunan Normal University, Changsha 410081, China
关键词:
seawater splitting;electrocatalyst;bifunctional water splitting;non-noble metal;porous material
摘要:
Given the abundant reserves of seawater and the scarcity of freshwater, real seawater electrolysis is a more economically appealing technology for hydrogen production relative to orthodox freshwater electrolysis. However, this technology is greatly precluded by the undesirable chlorine oxidation reaction and severe chloride corrosion at the anode, further restricting the catalytic efficiency of overall seawater splitting. Herein, a feasible strategy by engineering multifunctional collaborative catalytic interfaces is reported to develop porous metal nitride/phosphide heterostructure arrays anchoring on conductive Ni2P surfaces with affluent iron sites. Collaborative catalytic interfaces among iron phosphide, bimetallic nitride, and porous Ni2P supports play a positive role in improving water adsorption/dissociation and hydrogen adsorption behaviors of active Fe sites evidenced by theoretical calculations for hydrogen evolution reactions, and enhancing oxygenated species adsorption and nitrate-rich passivating layers resistant to chloride corrosion for oxygen evolution reaction, thus cooperatively propelling high-performance bifunctional seawater splitting. The resultant material Fe2P/Ni1.5Co1.5N/Ni2P performs excellently as a self-standing bifunctional catalyst for alkaline seawater splitting. It requires extremely low cell voltages of 1.624 and 1.742 V to afford current densities of 100 and 500 mA/cm2 in 1 M KOH seawater electrolytes, respectively, along with superior long-term stability, outperforming nearly all the ever-reported non-noble bifunctional electrocatalysts and benchmark Pt/IrO2 coupled electrodes for freshwater/seawater electrolysis. This work presents an effective strategy for greatly enhancing the catalytic efficiency of non-noble catalysts toward green hydrogen production from seawater electrolysis.