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Multi-scale defects in powder-based additively manufactured metals and alloys

journal of Materials Science & Technology 2022年第27期122卷 165-199页

作者： j.fu H.Li X.Song M.W.fu Department of Mechanical Engineering The Hong Kong Polytechnic UniversityHung HomKowloonHong KongChina State Key Laboratory of Solidification Processing School of Materials Science and EngineeringNorthwestern Polytechnical UniversityXi’an 710072China Department of Mechanical and Automation Engineering Chinese University of Hong KongShatinHong KongChina

Defect formation is a critical challenge for powder-based metal additive manufacturing(AM).Current understanding on the three important issues including formation mechanism,influence and control method of metal AM defects should be updated.In this review paper,multi-scale defects in AMed metals and alloys are identified and for the first time classified into three categories,including geometry related,surface integrity related and microstructural defects.In particular,the microstructural defects are further divided into internal cracks and pores,textured columnar grains,compositional defects and dislocation cells.The root causes of the multi-scale defects are discussed.The key factors that affect the defect formation are identified and analyzed.The detection methods and modeling of the multi-scale defects are briefly introduced.The effects of the multi-scale defects on the mechanical properties especially for tensile properties and fatigue performance of AMed metallic components are reviewed.Various control and mitigation methods for the corresponding defects,include process parameter control,post processing,alloy design and hybrid AM techniques,are summarized and discussed.From research aspect,current research gaps and future prospects from three important aspects of the multi-scale AM defects are identified and delineated.

关键词： Metal additive manufacturing Multi-scale defects Detection and modeling Mechanical properties Defect control and mitigation

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Granger causal representation learning for groups of time series

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Science China(Information Sciences) 2024年第5期67卷 56-68页

作者： Ruichu CAI Yunjin WU Xiaokai HUANG Wei CHEN Tom Z.j.fu Zhifeng HAO School of Computer Science Guangdong University of Technology Peng Cheng Laboratory College of Science Shantou University

Discovering causality from multivariate time series is an important but challenging problem.Most existing methods focus on estimating the Granger causal structures among multivariate time series,while ignoring the prior knowledge of these time series, e.g., the group of the time series. Focusing on discovering the Granger causal structures among groups of time series, we propose a Granger causal representation learning method to solve this problem. First, we use the multiset canonical correlation analysis method to learn the Granger causal representation of each group of time series. Then, we model the Granger causal relationships among the learned Granger causal representations using a recurrent neural network with temporal information. Finally, we formulate the above two stages into one unified optimization problem, which is efficiently solved using the augmented Lagrangian method. We conduct extensive experiments on synthetic and real-world datasets to validate the correctness and effectiveness of the proposed method.

关键词： Granger causal discovery Granger causal representation learning time series data recurrent neural network multiset canonical correlation analysis

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Improvement of Film Cooling Design for Turbine Vane Leading Edge Considering Combustor Outflow

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journal of Thermal Science 2024年第1期33卷 311-327页

作者： WANG Xinyu LIU Cunliang fu Zhongyi LI Yang ZHU Huiren School of Power and Energy Northwestern Polytechnical UniversityXi'an 710072China AECC Hunan Aviation Powerplant Research Institute Zhuzhou 412002China

As the interaction between the combustor and the turbine in the aero-engine continues to increase,the film cooling design considering the combustor swirling outflow has become the research focus.The swirling inflow and high-temperature gas first affect the vane leading edge(LE).However,no practical improved solution for the LE cooling design has been proposed considering the combustor swirling outflow.In this paper,the improved scheme of showerhead cooling is carried out around the two ways of adopting the laid-back-fan-shaped hole and reducing the coolant outflow angle.The film cooling effectiveness(η) and the coolant flow state are obtained by PSP(pressure-sensitive-paint) and numerical simulation methods,respectively.The research results show that the swirling inflow increases the film distribution inhomogeneity by imposing the radial pressure gradient on the vane to make the film excessively gather in some positions.The showerhead film cooling adopts the laid-back-fan-shaped hole to reduce the momentum when the coolant flows out.Although this cooling scheme improves the film attachment and increases the surface-averaged film cooling effectiveness(η_(sur)) by as much as15.4%,the film distribution inhomogeneity increases.After reducing the coolant outlet angle,the wall-tangential velocity of the coolant increases,and the wall-normal velocity decreases.Under the swirl intake condition,both ηand the film distribution uniformity are significantly increased,and the growth of η_(sur) is up to 16.5%.This paper investigates two improved schemes to improve the showerhead cooling under the swirl intake condition to provide a reference for the vane cooling design.

关键词： turbine vane showerhead cooling swirling inflow laid-back-fan-shaped hole film hole inclination

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Mechanical property of cylindrical sandwich shell with gradient core of entangled wire mesh

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Defence Technology（防务技术） 2024年第1期31卷 510-522页

作者： Xin Xue Chao Zheng fu-qiang Lai Xue-qian Wu Institute of Metal-rubber&Vibration Noise School of Mechanical Engineering and AutomationFuzhou UniversityFuzhou350116China fujian Metallurgical Industry Design Institute Fuzhou350116China

To explore the wide-frequency damping and vibration-attenuation performances in the application of aerospace components,the cylindrical sandwich shell structure with a gradient core of entangled wire mesh was proposed in this paper.Firstly,the gradient cores of entangled wire mesh in the axial and radial directions were prepared by using an in-house Numerical Control weaving machine,and the metallurgical connection between skin sheets and the gradient core was performed using vacuum brazing.Secondly,to investigate the mechanical properties of cylindrical sandwich shells with axial or radial gradient cores,quasi-static and dynamic mechanical experiments were carried out.The primary evaluations of mechanical properties include secant stiffness,natural frequency,Specific Energy Absorption(SEA),vibration acceleration level,and so on.The results suggest that the vibration-attenuation performance of the sandwich shell is remarkable when the high-density core layer is at the end of the shell or abuts the inner skin.The axial gradient material has almost no influence on the vibration frequencies of the shell,whereas the vibration frequencies increase dramatically when the high-density core layer approaches the skin.Moreover,compared to the conventional sandwich shells,the proposed functional grading cylindrical sandwich shell exhibits more potential in mass reduction,stiffness designing,and energy dissipation.

关键词： Entangled wire mesh Gradient cylindrical sandwich shell Vacuum brazing Secant stiffness Damping

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Effect of Ti and Ta content on the oxidation resistance of Co-Ni-based superalloys

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International journal of Minerals,Metallurgy and Materials 2024年第2期31卷 351-361页

作者： Yuheng Zhang Zixin Li Yunwei Gui Huadong fu jianxin Xie Beijing Advanced Innovation Center for Materials Genome Engineering University of Science and Technology BeijingBeijing 100083China Institute of Materials Intelligent Technology Liaoning Academy of MaterialsShenyang 110004China Key Laboratory for Advanced Materials Processing(MOE) University of Science and Technology BeijingBeijing 100083China Beijing Laboratory of Metallic Materials and Processing for Modern Transportation University of Science and Technology BeijingBeijing 100083China

Co-Ni-based superalloys are known for their capability to function at elevated temperatures and superior hot corrosion and thermal fatigue resistance.Therefore,these alloys show potential as crucial high-temperature structural materials for aeroengine and gas turbine hot-end components.Our previous work elucidated the influence of Ti and Ta on the high-temperature mechanical properties of alloys.However,the intricate interaction among elements considerably affects the oxidation resistance of alloys.In this paper,Co-35Ni-10Al-2W-5Cr-2Mo-1Nb-xTi-(5−x)Ta alloys(x=1,2,3,4)with varying Ti and Ta contents were designed and compounded,and their oxidation resistance was investigated at the temperature range from 800 to 1000℃.After oxidation at three test conditions,namely,800℃for 200 h,900℃for 200 h,and 1000℃for 50 h,the main structure of the oxide layer of the alloy consisted of spinel,Cr_(2)O_(3),and Al_(2)O_(3)from outside to inside.Oxides consisting of Ta,W,and Mo formed below the Cr_(2)O_(3)layer.The interaction of Ti and Ta imparted the highest oxidation resistance to 3Ti2Ta alloy.Conversely,an excessive amount of Ti or Ta resulted in an adverse effect on the oxidation resistance of the alloys.This study reports the volatilization of W and Mo oxides during the oxidation process of Co-Ni-based cast superalloys with a high Al content for the first time and explains the formation mechanism of holes in the oxide layer.The results provide a basis for gaining insights into the effects of the interaction of alloying elements on the oxidation resistance of the alloys they form.

关键词： Co-Ni-based superalloys high-temperature oxidation Ti and Ta elements formation mechanism of holes

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Nonlinear uncertainty impact of geometric variations on aerodynamic performance of low-pressure turbine blades with ultra-high loading under extreme operational conditions

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Chinese journal of Aeronautics 2024年第5期37卷 281-300页

作者： Xiaojing WANG Zhengping ZOU Chao fu Pengcheng DU School of Energy and Power Engineering Beihang UniversityBeijing 100191China National Key Laboratory of Science and Technology on Aero-Engine Aero-Thermodynamics Beihang UniversityBeijing 100191China Research Institute of Aero-Engine Beihang UniversityBeijing 100191China

Uncertainty impact of random geometric variations on the aerodynamic performance of low-pressure turbine blades is considerable,which is further amplified by the current ultra-high-lift design trend for weight reduction.Therefore,this uncertainty impact on ultra-highly loaded blades under extreme operational conditions near the margins with potential large-scale open separation is focused on in this study.It is demonstrated that this impact is significant,unfavourable,and nonlinear,which is clearly severer under extreme conditions.In addition to the overall attenuation and notable scattering of specific performance,the operational margins with open separation are also notably scattered with great risk of significant reduction.This scattering and nonlinearity are dominated by the variations in leading-edge thickness.The thinning of leading edge triggers local transition,enhancing downstream friction and reducing resistance to open separation,which is further exacerbated by operational deterioration.However,the opposite thickening yields less benefit,implying nonlinearity.This unfavourable impact highlights the need for robust aerodynamic design,where both a safer operational condition and a more robust blade are indispensable,i.e.,a compromise among performance,weight,and robustness.Besides the necessary limitation of loading levels,a mid-loaded design is recommended to reduce adverse pressure gradients in both the leading edge and rear region of the suction side,which helps to decrease the susceptibility of the transition and open separation to random perturbations.Similar improvements can also be achieved by appropriately thickening the leading edge.

关键词： Ultra-highly loaded turbine blade Geometric variations Uncertainty analysis Operational margins Robust aerodynamic design Nonlinearity

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Optimization of chemistry and process parameters for control of intermetallic formation in Mg sludges

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journal of Magnesium and Alloys 2024年第4期12卷 1431-1448页

作者： Y.fu G.G.Wang A.Hu Y.Li K.B.Thacker j.P.Weiler H.Hu Department of Mechanical Automotive and Materials EngineeringUniversity of Windsor401 Sunset AveWindsorOntario N9B 3P4Canada Global Technology Centre Meridian Lightweight Technologies25 MacNab AveStrathroyOntario N7G 4H6Canada

Intermetallic formation in sludge during magnesium(Mg)melting,holding and high pressure die casting practices is a very important issue.But,very often it is overlooked by academia,original equipment manufacturers(OEM),metal ingot producers and even die casters.The aim of this study was to minimize the intermetallic formation in Mg sludge via the optimization of the chemistry and process parameters.The Al8Mn5 intermetallic particles were identified by the microstructure analysis based on the Al and Mn ratio.The design of experiment(DOE)technique,Taguchi method,was employed to minimize the intermetallic formation in the sludge of Mg alloys with various chemical compositions of Al,Mn,Fe,and different process parameters,holding temperature and holding time.The sludge yield(SY)and intermetallic size(IS)was selected as two responses.The optimum combination of the levels in terms of minimizing the intermetallic formation were 9 wt.%Al,0.15 wt.%Mn,0.001 wt.%(10 ppm)Fe,690℃ for the holding temperature and holding at 30 mins for the holding time,respectively.The best combination for smallest intermetallic size were 9 wt.%Al,0.15 wt.%Mn,0.001 wt.%(10 ppm)Fe,630℃ for the holding temperature and holding at 60 mins for the holding time,respectively.Three groups of sludge factors,Chemical Sludge(CSF),Physical Sludge(PSF)and Comprehensive Sludge Factors(and CPSF)were established for prediction of sludge yields and intermetallic sizes in Al-containing Mg alloys.The CPSF with five independent variables including both chemical elements and process parameters gave high accuracy in prediction,as the prediction of the PSF with only the two processing parameters of the melt holding temperature and time showed a relatively large deviation from the experimental data.The Chemical Sludge Factor was primarily designed for small ingot producers and die casters with a limited melting and holding capacity,of which process parameters could be fixed easily.The Physical Sludge Factor could be used for mass production with a single type of Mg allo

关键词： Magnesium sludge Al-Mn intermetallic Optimization Taguchi method Sludge factor Chemical composition Process parameter

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Significant annealing-induced hardening effect in nanolaminate d-nanotwinne d(CrCoNi)_(97.4)Al_(0.8)Ti_(1.8)me dium-entropy alloy by severe cold rolling

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journal of Materials Science & Technology 2024年第3期170卷 156-166页

作者： Shuqing Yuan Hui fu Lei Qian Chi Fai Cheung Xu-Sheng Yang State Key Laboratory of Ultra-precision Machining Technology Department of Industrial and Systems EngineeringThe Hong Kong Polytechnic UniversityHung HomKowloonHong KongChina Hong Kong Polytechnic University Shenzhen Research Institute Shenzhen 518060China

Due to the easy coarsening caused by poor thermal stability,the verified annealing-induced hardening in nanograined metals can only maintain at a relatively low-temperature range.In this study,a nanolam-inated(CrCoNi)_(97.4)Al_(0.8)Ti_(1.8)medium-entropy alloy with an average lamellae thickness of∼20 nm embedded by thinner nanotwins was fabricated by severe cold rolling to achieve superior thermal stability.Compared with the conventional nanotwinned CrCoNi with nanotwins inside ultra-fined grains,the hier-archical nanolaminated-nanotwinned(CrCoNi)_(97.4)Al_(0.8)Ti_(1.8) exhibits a significant annealing-induced hard-ening effect,i.e.,hardness increasing from∼250 HV in the original specimen to∼500 HV in the cold-rolled status and finally∼630 HV after annealing at 600℃for 1 h.Detailed microstructure characterizations reveal that the reduced dislocation density and formation of L1_(2)ordered domain are mainly responsible for such hardening effect,which is facilitated by the effectively suppressed coarsening with annealing temperature,i.e.,slow detwinning process and well-retained low-angle nanolamellar structure.The coarsening mechanisms from the cold-rolled nanolamellae to the fully recrystallized micro-equiaxed structures under the annealing temperatures ranging from 400 to 800℃ were also elucidated by atomic observations.

关键词： Annealing-induced hardening Thermal stability Nanolaminated-nanotwinned structure CrCoNi Detwinning Grain boundary migration

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Circulating tumor cells shielded with extracellular vesicle-derived CD45 evade T cell attack to enable metastasis

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Signal Transduction and Targeted Therapy 2024年第5期9卷 2114-2131页

作者： Chuan Yang Xueping Wang Kenneth K.W.To Caimei Cui Min Luo Shaocong Wu Lamei Huang Kai fu Can Pan Zeyu Liu Teng Fan Caibo Yang Fang Wang Liwu fu State Key Laboratory of Oncology in South China Guangdong Provincial Clinical Research Center for CancerSun Yat-sen University Cancer CenterGuangzhou 510060P.R.China School of Pharmacy Faculty of MedicineThe Chinese University of Hong KongHong KongChina LABVIV Technology(Shenzhen)Co. LtdShenzhen 518057China

Circulating tumor cells(CTCs)are precursors of distant metastasis in a subset of cancer patients.A better understanding of CTCs heterogeneity and how these CTCs survive during hematogenous dissemination could lay the foundation for therapeutic prevention of cancer metastasis.It remains elusive how CTCs evade immune surveillance and elimination by immune cells.In this study,we unequivocally identified a subpopulation of CTCs shielded with extracellular vesicle(EVs)-derived CD45(termed as CD45^(+)CTCs)that resisted T cell attack.A higher percentage of CD45^(+)CTCs was found to be closely correlated with higher incidence of metastasis and worse prognosis in cancer patients.Moreover,CD45^(+)tumor cells orchestrated an immunosuppressive milieu and CD45^(+)CTCs exhibited remarkably stronger metastatic potential than CD45−CTCs in vivo.Mechanistically,CD45 expressing on tumor surfaces was shown to form intercellular CD45-CD45 homophilic interactions with CD45 on T cells,thereby preventing CD45 exclusion from TCR-pMHC synapse and leading to diminished TCR signaling transduction and suppressed immune response.Together,these results pointed to an underappreciated capability of EVs-derived CD45-dressed CTCs in immune evasion and metastasis,providing a rationale for targeting EVs-derived CD45 internalization by CTCs to prevent cancer metastasis.

关键词： CD45 metastasis prevention

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Effects of High-Definition Transcranial Direct Current Stimulation on Excitability of Spinal Motoneurons under Ankle Dorsi-Plantarflexion Fatigue Task

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Yiyong Shengwu Lixue/journal of Medical Biomechanics 2024年第2期39卷 293-298页

作者： Yu C. Zhan j. Shen B. Zhou j. Xu L. fu W. School of Rehabilitation Science Hangzhou Medical College Hangzhou 310000 China Key Laboratory of Exercise and Health Sciences of Ministry of Education Shanghai University of Sport Shanghai 200438 China Harvard Medical School 02115 MA United States Hebrew Senior Life Hinda and Arthur Marcus Institute for Aging Research 02131 MA United States

Objective To investigate the effects of high-definition transcranial direct current stimulation (HD-tDCS) on the modulation of the H-reflex and M-wave during ankle dorsiflexion-plantar flexion fatigue tasks to provide direction for the application of HD-tDCS in mitigating neuromuscular fatigue. Methods Twenty healthy young male participants were recruited and randomly assigned to either the real stimulation or sham stimulation group, with 10 participants in each group. The intervention consisted of a 5-day single-blind HD-tDCS application (duration: 20 min; intensity: 2 mA; target: Cz) . Baseline measurements of the H-reflex and M-wave under resting conditions, M-wave during maximal voluntary isometric contraction (MVIC) of the dorsiflexor muscle, and MVIC torque of the dorsiflexor and plantar flexor muscles were obtained. An ankle dorsiflexion fatigue task was performed to determine the time to achieve fatigue for the task. The same fatigue task was repeated and evaluated one day after the intervention. A repeated-measures two-factor (stimulation condition × pre / post fatigue) analysis of variance (ANOVA) was used to analyze the effects of independent variables on the mechanical properties of the muscles and α-motoneuron conduction characteristics. Results After fatigue, voluntary activation (VA), maximal H-reflex (Hmax ), maximal M-wave (Mmax ), and dorsiflexor and plantar flexor MVIC torques in both groups were significantly reduced compared with pre-fatigue levels (P junction under the ankle dorsi-plantarflexion fatigue task. © 2024 Editorial Department of journal of Shanghai Second Medical University. Al

关键词： corticospinal pathway high-definition transcranial direct current stimulation (HD-tDCS) maximal voluntary isometric contraction (MVIC) muscle fatigue neural impulses α-motoneuron activity

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