Showing papers by "Harbin Engineering University published in 2023"

Microstructure and mechanical properties of aluminum-steel dissimilar metal welded using arc and friction stir hybrid welding

Abstract: In this study, arc and friction stir hybrid welding (AFSHW) was proposed to weld aluminum-steel dissimilar metals in attempt to realize high quality joining. Firstly, an interlayer was produced on galvanized steel by using bypass current-metal inert gas welding (BC-MIG), and then an aluminium plate was jointed via Friction stir lap welding (FSLW). The effects of tool pin length and FSLW times on the microstructure and mechanical properties of dissimilar joints were fully investigated by means of Optical Microscopy (OM), Scanning Electron Microscope (SEM), Electron Backscatter Diffraction (EBSD), and mechanical testing. The results show that as pin length increased, joint strength tended to increase and then decrease, and the tensile failure partially occurred at aluminium base metal. However, with additional number of FSLW, joint strength would be reduced, which was attributed to attenuated dislocation density and strain concertation in dissimilar joint. The research outcomes will provide a new welding method to obtain sound Al-Fe dissimilar metal joint, and benefit to a better understanding of Al-Fe joining mechanism.

Engineering Escherichia coli for high-yield production of ectoine

Abstract: Ectoine is a natural macromolecule protector and synthesized by some extremophiles. It provides protections against radiation-mediated oxidative damages and is widely used as a bioactive ingredient in pharmaceutics and cosmetics. To meet its growing commercial demands, we engineered Escherichia coli strains for the high-yield production of ectoine. The ectABC gene cluster from the native ectoine producer Halomonas elongata was introduced into different E. coli strains via plasmids and 0.8 g L-1 of ectoine was produced in flask cultures by engineered E. coli BL21 (DE3). Subsequently, we designed the ribosome-binding sites of the gene cluster to fine-tune the expressions of genes ectA, ectB, and ectC, which increased the ectoine yield to 1.6 g L-1. After further combinatorial overexpression of Corynebacterium glutamicum aspartate kinase mutant (G1A, C932T) and the H. elongate aspartate-semialdehyde dehydrogenase to increase the supply of the precursor, the titer of ectoine reached to 5.5 g L-1 in flask cultures. Finally, the engineered strain produced 60.7 g L-1 ectoine in fed-batch cultures with a conversion rate of 0.25 g/g glucose.

Simultaneous Improvement of Strength, Ductility and Damping Capacity of Single β-Phase Mg–Li–Al–Zn Alloys

Abstract: Body-centered cubic (BCC) Mg–Li alloy can be effectively strengthened by with the addition of Al and Zn. However, adding excessive amounts result in reduced mechanical properties and damping capacity of the alloy during subsequent heat treatment and deformation. The effects of solution-hot rolling-aging on the mechanical properties and damping capacity of LAZ1333 alloy and LAZ1366 alloy were studied. The solid solution strengthening greatly increases the hardness of the alloy, but the ductility is extremely poor. The AlLi softening phase precipitated during the subsequent hot rolling and aging process greatly improves the ductility of the alloy, but the excess precipitation of in the AlLi softening phase and the solid solution of excess Zn element are not conducive to the substantial improvement of the strength and ductility of the alloy. Excessive addition of alloying elements is detrimental to the damping capacity of the alloy, but the damping capacity of the alloy can be significantly improved by depleting the number of solute atoms through subsequent ageing treatments. The UTS and FE of as-cast LAZ 1333 alloy are 111 MPa and 16.9%, respectively. The as-aged LAZ1333 alloy has the best mechanical properties and damping capacity, and the UTS and FE are increased by 65.8% and 89.3%, respectively, compared to the as-cast alloy, and the damping capacity increased from 0.011 to 0.015.

Achieving superior low-temperature toughness in high-strength low-carbon steel via controlling lath boundary segregation

Abstract: The optimal aging temperatures of 400–550 °C for high strength steels falls into the dangerous temperature range of temper-embrittlement. To obtain a good low-temperature toughness, temperatures above 600 °C are usually selected for aging treatments, resulting in a huge loss of strength. In this work, the effects of aging treatments at 500 and 550 °C on the impact performance of a Cu precipitation-strengthened steel at a low temperature of −80 °C were systematically investigated. The solute segregation at lath boundaries is found to be the main factor controlling the low-temperature toughness. Excellent impact performance of ∼180 J at −80 °C along with a high yield strength of ∼1050 MPa and a total elongation of 19% can be obtained by controlling the segregation of solute elements, specifically Mo and Mn at the lath boundaries. The evolutions of matrix and precipitates during aging treatments were investigated. The strengthening and toughening mechanisms are also critically discussed.

Robust superhydrophobic Ni-Co electrodeposited carbon felt for hot water repellency and controllable oil/water separation

Abstract: This study proposes a new recipe to manufacture robust superhydrophobic porous materials with magnetic properties that repel hot water. Through galvanostatic electrodeposition, the surface of carbon fibers in the carbon felt is entirely covered by the Ni-Co alloy coating with nano-protrusions and a thickness of about 2 µm. Under thermal annealing at 60 ℃, the resulting surface demonstrates diminishing wettability over time, and even superhydrophobicity after 12 h treatment. Meanwhile, when subjected to high compression force and cyclic abrasion, the as-prepared carbon felt displays robust superhydrophobicity. Due to the high porosity and fibrous structure, the Ni-Co coated carbon felt also exhibits high repellency to hot water as high as 90 ℃. In addition, the newly developed superhydrophobic carbon felt can be employed for oil/water separation in complex structures by controlling its movement through a magnet. The employed strategy can help reduce the potential pollution caused by environmentally hazardous low surface energy substances when using superhydrophobic materials and exhibit promising applications in oil/water separation fields for special scenes, e.g., hot liquids and intricate pipelines.

A hybrid analytic–numerical formulation for the vibration analysis of a cylindrical shell coupled with an internal flexural floor structure

Abstract: A hybrid analytic–numerical formulation is developed to study the vibration behaviors of a cylindrical shell coupled with an internal flexural floor structure. The full structure is divided into a cylindrical shell, axisymmetric annular plates and a non-axisymmetric floor structure. The cylindrical shell and annular plates are analyzed by the analytic dynamic stiffness method (DSM) while the floor is modeled by the finite element method (FEM), so the line connections between the cylindrical shell and interior floor degrade into discrete point connections. At each coupling point, virtual springs are used to couple the cylindrical shell and interior floor, and coupling conditions at six Dofs are fully taken into consideration. In DSM, the displacement solutions of the cylindrical shell and annular plate are described by exponential functions and Bessel functions, respectively. In FEM, the dynamic condensation technique is adopted to reduce the model Dofs, while the main dynamic characteristic of the FEM model is preserved as much as possible. To verify the accuracy and effectiveness of present formulation, vibration results calculated by present method are compared with those obtained from FEM and a test experiment. Moreover, the effects of ribs, bulkheads, coupling conditions, boundary conditions of the shell and structural damping on the vibration responses are also investigated.

Research on the Incentive Mechanism of Publishing Editors Based on Psychological Contract

Abstract: In the era of the knowledge economy, the editor is the core resource element of the publishing organization. Taking the different dimensions of the psychological contract as the knowledge effect of editors in publishing organizations, a conceptual model to explore the satisfaction of editors and publishing organizations is established, and the empirical test is carried out by means of questionnaires. The research results show that the cultural identity of the publishing organization, the people-oriented management concept, and the high trust of the organization have a significant positive impact on the editor's satisfaction; the working environment of the publishing organization has a certain mediating effect on the editor's satisfaction. The research results clarify the mechanism of the relationship between the publishing organization and the editor, reveal the essence of affecting the editor's satisfaction, and provide theoretical guidance for the management practice of the publishing organization.

Theories of International Trade and Competitiveness

Abstract: TheCountry-based theories economic knowledge in the sphere of international trade goes back centuries and covers almost all schools of economic thought.

Market Structures

Abstract: Understand the concepts of market, market structureMarket structure, and market concentrationMarket concentration

Fuel Consumption Prediction Models Based on Machine Learning and Mathematical Methods

Abstract: An accurate fuel consumption prediction model is the basis for ship navigation status analysis, energy conservation, and emission reduction. In this study, we develop a black-box model based on machine learning and a white-box model based on mathematical methods to predict ship fuel consumption rates. We also apply the Kwon formula as a data preprocessing cleaning method for the black-box model that can eliminate the data generated during the acceleration and deceleration process. The ship model test data and the regression methods are employed to evaluate the accuracy of the models. Furthermore, we use the predicted correlation between fuel consumption rates and speed under simulated conditions for model performance validation. We also discuss applying the data-cleaning method in the preprocessing of the black-box model. The results demonstrate that this method is feasible and can support the performance of the fuel consumption model in a broad and dense distribution of noise data in data collected from real ships. We improved the error to 4% of the white-box model and the R2 to 0.9977 and 0.9922 of the XGBoost and RF models, respectively. After applying the Kwon cleaning method, the value of R2 also can reach 0.9954, which can provide decision support for the operation of shipping companies.

Efficient Hydrogen Evolution Catalysts Based on Hierarchical Flowerlike Ni_<i>x</i>Co_9–<i>x</i>S₈ Nanosheets

Abstract: In terms of the need for a low-carbon economy and alleviating the need for energy security, hydrogen (H2) plays a key role in promoting a sustainable economy because it is clean and efficient. The bottleneck of the hydrogen evolution reaction (HER) can be overcome by developing high-efficiency electrocatalysts. Using a simple solvothermal method, p-NixCo9–xS8 with polyvinylpyrrolidone (PVP) compounds are successfully prepared with synergistic effects between bimetallic sulfides. The resulting p-NixCo9–xS8 catalyst shows a hierarchical flowerlike nanosheet shape based on physical representations. An ultrathin and porous nanosheet surface facilitates rapid electrolyte injection and provides abundant active sites for H+ adsorption, thus giving p-NixCo9–xS8 nanosheets outstanding HER performance. Furthermore, the synergistic effect of a bimetallic electrocatalyst is helpful to improve HER activity. In comparison to NixCo9–xS8 nanosheets without PVP, individual Co9S8 particles, and individual Ni9S8 nanosheets, p-NixCo9–xS8 nanosheets have a lower overpotential (137 mV to 10 mA cm–2), Tafel slope (109 mV dec–1), and 95.7% retention of current after 1000 cycles in the HER process.

Economic Cycles

Abstract: Understand the concepts of cyclicityCyclicity and economic cycleEconomic cycle

Liberalization and Protectionism

Abstract: Each country establishes a balance between the economic development.

TMT's technical orientation and ambidextrous innovation capability in digital transformation age

Abstract: This study examines the effects of technical orientation of the top management team (TMT) on ambidextrous innovation capability in the digital transformation age. Our baseline results document a positive relationship between TMTs' technical orientation and ambidextrous innovation capability. While digital transformation significantly enhances the positive relationship between TMTs' technical orientation and radical innovation capability, it is not correlated with the positive relationship between TMTs' technical orientation and incremental innovation capability. We discuss the heterogeneity of state ownership, revealing that while TMTs' technical orientation enhances the ambidextrous innovation capability in Chinese state-owned enterprises (SOEs), it is not correlated with Chinese non-SOEs. In Chinese SOEs, digital transformation enhances the positive relationship between TMTs' technical orientation and ambidextrous innovation capability, but no correlation is observed in Chinese non-SOEs.

Effect of Financial Support on the Development of Marine Equipment Manufacturing Industry in China—Evidence from 30 Listed Companies

Abstract: Marine equipment manufacturing industry is an important priority development area defined in China’s “14th Five-Year Plan” and Made in China 2025. It is an important foundation and guarantee for China to realize the strategy of building a powerful marine power. In its development process, financial support plays an irreplaceable role. This paper selects China’s marine equipment manufacturing industry as the research object, constructs the financial service support system from the three perspectives of direct, indirect and policy, and collects the financial data and financial indicators of 30 listed companies in China's marine equipment manufacturing industry from 2011 to 2020, so as to establish a dynamic panel model and make an empirical analysis. The results show that the equity financing rate has a negative effect on the development of sample marine equipment enterprises, and the government subsidy rate has a positive effect on the sample enterprises, while the borrowing rate of financial institutions and the commercial credit rate have no significant influence on the development of sample enterprises. According to the current situation analysis of financial support and sys-GMM empirical research, explore the ways of financial support, so as to promote the sound and rapid development of China's marine equipment manufacturing industry.