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A NOVEL METHOD FOR EVALUATING PLANE STRESS DYNAMIC FRACTURE TOUGHNESS OF 0Cr18Ni10Ti STAINLESS STEEL WELDED jOINTS

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Acta Metallurgica Sinica(English Letters) 2008年第4期21卷 303-312页

作者： z.j. Xu Y.L. Li School of Aeronautics Northwestern Polytechnical University Xi＇an 710072 China

A novel method was proposed for the evaluation of Mode I dynamic fracture toughness （DFT） under plane stress and small scale yielding conditions for welded joints of stainless steel （SS）, 0Cr18Ni10Ti. In a hybrid experimental-numerical approach, the experiments were carried out on the Hopkinson pressure bar apparatus, and three dimensional （3D） transient numerical simulations were performed by a finite element （FE） computer program. Macroscopical plastic deformation was observed at the loading and supporting points, on the specimens, after the test, which could cause a large error if omitted in the numerical simulation. Therefore, elustic-viscoplustic analysis was performed on the specimen by adopting the johnson-Cook （j-C） model to describe the rate-dependent plastic flow behavior of the material. The material heterogeneity in the mismatched welded joints, induced by the difference in the base metal （BM） and the weld metal （WM） in yield stress, has also been taken into consideration by using the j-C models separately. Good accordance was obtained between the experimental and the computational results by the present approach. The relationship between plane stress DFT and loading rate was also obtained on the order of 108 MPa.m^1/2.s^-1.

关键词： 0Cr18Ni10Ti Welded joint High strain rate Dynamic fracture Plane stress

REAL-TIME FLOOD FORECASTING MODELING OF 1D UNSTEADY CHANNEL FLOW AND KALMAN FILTER

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journal of Hydrodynamics 2001年第1期13卷 64-69页

作者： Li, z.j. Weng, M.H. Coll. of Water Res. and Environ. Hohai Univ. Nanjing 210024 China

The model of 1D unsteady channel flow combined with the Kalman filter for real-time channel flood forecasting was attempted. The suitable upstream and downstream boundary conditions were suggested. The system equation was given by the linearization of the finite difference equations of the mass conservation and momentum equations as well as the boundary conditions. In the Kalman filter updating model, because the number of measurement variable is less than that of state-space variables, the measurement error covariance matrix could be estimated in real time through the innovation sequence, and the system error covariance matrix needs to be estimated preliminarily. A real example of flood forecasting in the Huaihe River was given to explain how the method works. The results show that the model is reasonable and effective.

关键词： Channel flow Computer simulation Kalman filtering Unsteady flow

INVESTIGATION OF LASER BEAM WELDING PROCESS OF Az61 MAGNESIUM-BASED ALLOY

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Acta Metallurgica Sinica(English Letters) 2006年第4期19卷 287-294页

作者： H.Y. Wang z.j. Li Industrial Center Shenzhen Polytechnic Shenzhen 518055 China

Laser welling process of Az61 magnesium alloys is investigated using a special CO2 laser experimental system. The effect of processing parameters including laser power, welling speed, and protection gas flow at the top and bottom is researched. The results show that an ideal well bead can be formed by choosing the processing parameters properly. An optimized parameter range is obtained by a large number of experiments. Among them, laser power and welling speed are the two main parameters that determine the well width and dimensions. The protect gas flow rate has a slight effect on the well width, but it directly effects the surface color of the well. The test results for typical welds indicate that the microhardness and tensile strength of the well zone are better than that of the base metal A fine-grained well region has been observed and no obvious heat-affected zone is found. The well zone mainly consists of small α-Mg phase, （α ＋ Al12Mg17）, and other eutectic phases. The small grains and the eutectic phases in the joint are believed to play an important role in the increase of the strength of wells for Az61 magnesium alloys.

关键词： magnesium alloy laser beam welding laser power welling speed

An SBFEM-Based Model for Hydraulic Fracturing in Quasi-Brittle Materials

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Acta Mechanica Solida Sinica 2018年第4期31卷 416-432页

作者： F. Yao z.j. Yang Y.j. Hu College of Civil Engineering and Architecture Zhejiang University Hangzhou 310058 China School of Civil Engineering Shaoxing University Shaoxing 312000 China

A numerical model based on the scaled boundary finite element method is devel- oped to simulate the hydraulic fracturing in concrete-like quasi-brittle materials using cohesive interface elements. The shadow domain method developed previously （Yang and Deeks in Eng Fract Mech 143（4）：333 354, 2007） is extended to consider crack-width-dependent hydraulic pres- sure and cohesive traction, so that the stress intensity factors caused by both crack-face forces are semi-analytically calculated separately in the same way. The crack propagation is determined by the criterion of KI ≥ 0, and the propagation direction by the linear elastic fracture mechanics criteria. Two examples of concrete structures are modeled, and the results are in good agreement with the experimental data and others numerical results.

关键词： Scaled boundary finite element method Hydraulic fracture Cohesive crackmodel Crack propagation

CONSTITUTIVE RELATIONSHIP OF IN718 ALLOY FOR THERMOVISCOPLASTIC AND MICROSTRUCTURE EVOLUTION COUPLED ANALYSIS

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Acta Metallurgica Sinica(English Letters) 2007年第5期20卷 373-379页

作者： D. Liu Y.H. Yang j. Geng z.j. Luo School of Materials Science Northwestern Polytechnical University Xi＇an 710072 China

The interaction between thermomechanical parameters and microstructure evolution is so intense that it must be considered during the finite element method （FEM） simulation of the hot plastic working process, for materials that are difficult to deform. Taking the microstructure evolution into account, a novel type of constitutive relationship has been put forward for the IN718 alloy. The microstructure evolution model was first established for the dominant microstructure evolution processes. Then the microstructure evolution models and the method to determine the local flow stress of the corresponding microstructure for current thermomechanical parameters and deformation history were presented. Once the local flow stresses of different structures and their volume contributions were defined, the apparent flow stress of the material could be determined as the weighted sum of the local flow stresses and volume contributions. To validate the proposed method, a thermoviscoplastics and microstructure evolution coupled analysis for a forging process of a critical IN718 disk forging was performed. The predicting results were in close agreement with the experimental data.

关键词： constitutive relationship microstructure evolution numerical simulation IN718 alloy

MECHANISM AND KINETICS OF TRANSFORMATION OF ALUMINA INCLUSIONS BY CALCIUM TREATMENT

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Acta Metallurgica Sinica(English Letters) 2006年第1期19卷 1-8页

作者： z.j. Han L. Liu M. Lind L. Holappa Central Iron and Steel Research Institute Beijing 100081 China Laboratory of Metallurgy Helsinki University of Technology P.O. Box 6200Espoo 02015 Finland

The basic mechanism and kinetics of the transformation process of alumina inclusions in steel was reported when calcium introduced into the steel by wire feeding orpowder injection. To clarify the mechanisms model, experiments were performed by studying reactions between AltOs and CaO in a laboratory furnace and by performing calcium treatments in an 8kg induction furnace for Al deoxidised melt. The phases formed during the reaction between Al2O3 and CaO were examined by SEM-EDS （scanning electron microscope-energy dispersive spectrometer）, and the reaction sequence of Al2O3=〉 CA6=〉 CA2 =〉 CA =〉 CAx（l） was discussed in term of the experimental observations. The kinetics of the reaction of calcium with alumina inclusions were simulated by immersing alumina plates in a Ca treated steel melt in the induction furnace. Results were compared with observations of real inclusion transformation. A kinetic model was proposed based on the results.

关键词： mechanism kinetics alumina inclusion transformation

The compound(E)-2-(3,4-dihydroxystyryl)-3-hydroxy-4H-pyran-4-one alleviates neuroinflammation and cognitive impairment in a mouse model of Alzheimer's disease

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Neural Regeneration Research 2025年第11期20卷 3330-3344页

作者： Xueyan Liu Wei Wu Xuejuan Li Chengyan Wang Ke chai Fanru Yuan Huijuan zheng Yuxing Yao Chenlu Li zu-Cheng Ye Daijun zha Department of Medicinal Chemistry School of PharmacyFujian Medical UniversityFuzhouFujian ProvinceChina Fujian Provincial Key Laboratory of Brain Aging and Neurodegenerative Diseases School of Basic Medical SciencesFujian Medical UniversityFuzhouFujian ProvinceChina Institute of Laboratory Animal Center Fujian Medical UniversityFuzhouFujian ProvinceChina Department of Neurosurgery Neurosurgery Research InstituteThe First Affiliated HospitalFujian Medical UniversityFuzhouFujian ProvinceChina Department of Hyperbaric Oxygen National Regional Medical CenterBinhai Campus of the First Affiliated HospitalFujian Medical UniversityFuzhouFujian ProvinceChina

Previous studies have shown that the compound(E)-2-(3,4-dihydroxystyryl)-3-hydroxy-4H-pyran-4-one(D30),a pyromeconic acid derivative,possesses antioxidant and anti-inflammatory properties,inhibits amyloid-β aggregation,and alleviates scopolamine-induced cognitive impairment,similar to the phase Ⅲ clinical drug *** this study,we established a mouse model of Alzheimer's disease via intracerebroventricular injection of fibrillar amyloid-β to investigate the effect of D30 on fibrillar amyloid-β-induced *** results showed that D30 alleviated fibrillar amyloid-β-induced cognitive impairment,promoted fibrillar amyloid-β clearance from the hippocampus and cortex,suppressed oxidative stress,and inhibited activation of microglia and astrocytes.D30 also reversed the fibrillar amyloid-β-induced loss of dendritic spines and synaptic protein ***,we demonstrated that exogenous fibrillar amyloid-βintroduced by intracerebroventricular injection greatly increased galectin-3 expression levels in the brain,and this increase was blocked by *** the role of D30 in clearing amyloid-β,inhibiting neuroinflammation,protecting synapses,and improving cognition,this study highlights the potential of galectin-3 as a promising treatment target for patients with Alzheimer's disease.

关键词： Alzheimer's disease amyloid-β astrocyte cognitive impairment D30 dendritic spines galectin-3 microglia neuroinflammation neuron

XPS INVESTIGATION OF NITROGEN IONS IMPLANTED INTO ALUMINUM ALLOY BY PLASMA BASED ION IMPLANTATION

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Acta Metallurgica Sinica(English Letters) 1999年第5期12卷 771-776页

作者： zhan, z.j. Ma, X.X. Xia, L.F. Sun, Y. Harbin Inst of Technology Harbin China

Aluminum alloy 2024 has been implanted with nitrogen ions at various doses by plasma based ion implantation. The introduction of energetic ions causes structural change within the near surface region of the solid. The samples have been characterized by X-ray Photoelectron Spectroscopy at various depths. The chemical states of Al and N were identified by deconvolution of the recorded XPS spectra. After plasma based ion implanted nitrogen into aluminum, not only the AlN precipitates but also super saturated solution of nitrogen forms. The presence of aluminum in different chemical states is corresponding to Al, AlN and Al2O3. The majority of nitrogen is in the form of the supersaturated solution. With the increase of nitrogen dose, the amount of AlN precipitates increases.

关键词： Aluminum compounds Ion implantation Nitrides Nitrogen Plasma devices Wear of materials

Effect of scanning strategy on grain structure and crystallographic texture of Inconel 718 processed by selective laser melting

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journal of Materials Science & Technology 2018年第10期34卷 1799-1804页

作者： H.Y. Wan z.j. zhou C.P. Li G.F. Chen G.P. zhang Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China School of Materials Science and Engineering University of Science and Technology of China Shenyang 110016 China Materials & Manufacturing Qualification Group Corporate Technology Siemens Ltd. Beijing 100102 China

Two types of scanning strategies were adopted to study the effect of scanning strategy on grain structure and crystallographic texture of selective laser melted （SLM） Inconel 718. The results show that bidirec-tional scanning without and with a 90°-rotation for every layer produced the bimodal grain structure and the directional columnar grain structure, respectively. Controlling the heat flux direction between the successive layers via scanning strategy enabled the formation of such different grain structures. Fur-thermore, when the 90°-rotation was applied, the competitive grain growth mechanism became more pronounced and the strong cube texture developed.

关键词： Selective laser melting Additive manufacturing Scanning strategy Texture Grain structure