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Toward an understanding of dwell fatigue damage mechanism of bimodal Ti-6Al-4V alloys

Journal of Materials Science & Technology 2022年第13期108卷 244-255页

作者： l.r.zeng l.M.lei X.M.luo G.P.Zhang Shenyang National laboratory for Materials Science Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China School of Mechanical Engineering Chengdu UniversityChengdu 610106China AECC Shanghai Commercial Aircraft Engine Manufacturing Co. Ltd.Shanghai 201306China

Dwell fatigue effect is a long-standing problem threatening the long-term service reliability for fan blades and fan disks of an aircraft *** understand the basic mechanism of dwell fatigue damage,pure fatigue and 60 s dwell fatigue properties of bimodal Ti-6Al-4V alloys with different volume fractions of the primaryα(α_(p))phase were examined *** results showed that both pure fatigue and dwell fatigue life decreased with increasing the volume fraction of theα_(p)phase and the dwell fatigue life was lower than the pure fatigue *** quasi-in-situ test results and the quantitative characterization of damage behaviors of the local microstructure units defined by theα_(p)-secondaryα(α_(s))combination reveal that theα_(s)phase close to theα_(p)phase with extensively slip activities was gradually damaged under dwell fatigue loading,while that under pure fatigue loading was undamaged,demonstrating that the dwell loading induced the damage of theα_(s)phase,and further reduced the fatigue life.A stress relaxation-based model is proposed to describe the physical mechanism on dwell fatigue damage of the bimodal Ti-6Al-4V alloy,*** elastic deformation of theα_(s)phase caused by the strain incompatibility would be gradually transformed into plastic deformation during the dwell stage,and thus promotes fatigue *** model provides new insights into the microscopic process of stress/strain transfer between the soft and hard microstructure units under dwell fatigue loading.

关键词： Dwell effect Fatigue damage Stress relaxation Volume fraction of primaryαphase Quasi-in-situ testing

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Influence of alloy element partitioning on strength of primary α phase in Ti-6Al-4V alloy

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Journal of Materials Science & Technology 2018年第5期34卷 782-787页

作者： l.r.zeng H.l.Chen X.li l.M.lei G.P.Zhang Shenyang National laboratory for Materials Science Institute of Metal Research Chinese Academy of Sciences Shenyang 110016 China University of Chinese Academy of Sciences Beijing 100049 China School of Materials Science and Engineering University of Science and Technology of China Shenyang 110016 China AVIC Commercial Aircraft Engine Co.LTD Shanghai 200241 China

The partitioning effect of Al（α-phase stabilizer） and V elements（β-phase stabilizer） on strength of the primary α phases in the α/β Ti-6 Al-4 V alloy with the bimodal microstructure was *** was found that partitioning of Al and V elements took place in the Ti-6 Al-4 V alloy during the recrystallization process,leading to the variation of the content of Al and V elements in the primary α phases with changing the volume fraction of the primary α *** tests reveal a general trend that the strength of the primary α phases increases with decreasing the volume fraction of the primary α phases,and such trend is independent on the loading direction relative to the c-axis of the α *** enhanced strength is attributed to the increase of the content of Al element in the primary α phase,but it is not dominated evidently by the change of the V *** solid solution strengthening contributed from both the elastic strain introduced by the solute atoms and the variation of the density of states was estimated theoretically.

关键词： Ti-6Al-4V Nanoindentation Strength Alloy element partitioning Crystallographic orientation

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Differential Evolution of High-Pressure and Ultrahigh-Pressure Metapelites from Habutengsu, Chinese Western Tianshan: Phase Equilibria Modelling and ^(40)Ar/^(39)Ar Geochronology

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Acta Geologica Sinica(English Edition) 2016年第2期90卷 628-640页

作者： lü zeng ZHANG lifei The Key laboratory of Orogenic Belts and Crustal Evolution School of Earth and Space SciencesPeking University

Metapelite is one of the predominant rock types in the high-pressure–ultrahigh-pressure（HP–UHP） metamorphic belt of western Tianshan, NW China; however, the spatial and temporal variations of this belt during metamorphism are poorly understood. In this study, we present comparative petrological studies and 40^Ar/39 ^Ar geochronology of HP and UHP pelitic schist exposed along the Habutengsu valley. The schist mainly comprises quartz, white mica, garnet, albite and bluish amphibole. In the Mn O–Na2O–Ca O–K2O–Fe O–Mg O–Al2O3–Si O2–H2O（Mn NCKFMASH） system, P–T pseudosections were constructed using THErMOCAlC 333 for two representative pelitic schists. The results demonstrate that there was a break in the peak metamorphic pressures in the Habutengsu area. The northern schist has experienced UHP metamorphism, consistent with the presence of coesite in the same section, while the southern one formed at lower pressures that stabilized the quartz. This result supports the previous finding of a metamorphic gradient through the HP–UHP metamorphic belt of the Chinese western Tianshan by the authors. Additionally, phengite in the northern schist was modelled as having a Si content of 3.55–3.70（a.p.f.u.） at the peak stage, a value much higher than that of oriented matrix phengite（Si content 3.32–3.38 a.p.f.u.）. This indicates that the phengite flakes in the UHP schist were subjected to recrystallization during exhumation, which is consistent with the presence of phengite aggregates surrounding garnet porphyroblast. The 40^Ar/39^ Ar age spectra of white mica（dominantly phengite） from the two schists exhibit similar plateau ages of ca. 315 Ma, which is interpreted as the timing of a tectonometamorphic event that occurred during the exhumation of the HP–UHP metamorphic belt of the Chinese western Tianshan.

关键词： pelitic schist HP–UHP metamorphism P–T pseudosection 40^Ar/39^Ar geochronology Chinese western Tianshan

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reducing metal artifacts by restricting negative pixels

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Visual Computing for Industry,Biomedicine,and Art 2021年第1期4卷 142-151页

作者： Gengsheng l.zeng Megan zeng Department of Computer Science Utah Valley UniversityOremUT 84058USA Department of radiology and Imaging Sciences University of UtahSalt Lake CityUT 84108USA Department of Electrical Engineering and Computer Science University of California at BerkeleyBerkeleyCA 94720USA

When the object contains metals,its x-ray computed tomography(CT)images are normally affected by streaking *** artifacts are mainly caused by the x-ray beam hardening effects,which deviate the measurements from their true *** interesting observation of the metal artifacts is that certain regions of the metal artifacts often appear as negative pixel *** novel idea in this paper is to set up an objective function that restricts the negative pixel values in the *** must point out that the naïve idea of setting the negative pixel values in the reconstructed image to zero does not give the same *** paper proposes an iterative algorithm to optimize this objective function,and the unknowns are the metal affected *** the metal affected projections are estimated,the filtered backprojection algorithm is used to reconstruct the final *** paper applies the proposed algorithm to some airport bag CT *** bags all contain unknown metallic *** metal artifacts are effectively reduced by the proposed algorithm.

关键词： Filtered backprojection image reconstruction Iterative algorithm Metal artifact reduction Objective function X-ray computed tomography

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Coesite in metasediments from the Muzhaerte valley, southwestern Tianshan

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Science Bulletin 2019年第2期64卷 78-80页

作者： zeng lü lifei Zhang Ji Yue Key laboratory of Orogenic Belts and Crustal Evolution School of Earth and Space Sciences Peking University

The sediments,including calcareous,siliciclastic and volcanoclastic,usually occupy>90%in volume of an accretionary complex and thus,if involved in subduction zones,their maximum return depths(i.e.,peak pressures)are fundamental to unravel the geodynamic processes during the convergence of plates[1].As a unique example of accreted complex returned from sub-arc depths(>90 km)worldwide.

关键词： UHP southwestern Tianshan Coesite in metasediments from the Muzhaerte valley

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Iterative analytic extension in tomographic imaging

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Visual Computing for Industry,Biomedicine,and Art 2022年第1期5卷 44-56页

作者： Gengsheng l.zeng Department of Computer Science Utah Valley UniversityOremUT 84058USA Department of radiology and Imaging Sciences University of UtahSalt Lake CityUT 84108USA

If a spatial-domain function has a finite support,its Fourier transform is an entire *** Taylor series expansion of an entire function converges at every finite point in the complex *** analytic continuation theory suggests that a finite-sized object can be uniquely determined by its frequency components in a very small *** to obtain such an exact Taylor expansion is *** paper proposes an iterative algorithm to extend the measured frequency components to unmeasured *** simulations show that the proposed algorithm converges very slowly,indicating that the problem is too ill-posed to be practically solvable using available methods.

关键词： Analytic continuation Entire function Iterative projections onto convex sets algorithm Image reconstruction limited angle tomography

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A projection-domain iterative algorithm for metal artifact reduction by minimizing the total-variation norm and the negative-pixel energy

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Visual Computing for Industry,Biomedicine,and Art 2022年第1期5卷 1-11页

作者： Gengsheng l.zeng Department of Computer Science Utah Valley UniversityOremUT 84058USA Department of radiology and Imaging Sciences University of UtahSalt Lake CityUT 84108USA

Metal objects in X-ray computed tomography can cause severe *** state-of-the-art metal artifact reduction methods are in the sinogram inpainting category and are iterative *** paper proposes a projectiondomain algorithm to reduce the metal *** this algorithm,the unknowns are the metal-affected projections,while the objective function is set up in the image *** data fidelity term is not utilized in the objective *** objective function of the proposed algorithm consists of two terms:the total variation of the metalremoved image and the energy of the negative-valued pixels in the *** the metal-affected projections are modified,the final image is reconstructed via the filtered backprojection *** feasibility of the proposed algorithm has been verified by real experimental data.

关键词： Analytical image reconstruction Metal artifact reduction Projection-domain iterative algorithm X-ray computed tomography

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ANAlYSIS OF STrESS CONCENTrATIONS IN UNIDIrECTIONAl COMPOSITES TAKING INTO ACCOUNT THE TENSIlE lOAD IN THE MATrIX

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Acta Mechanica Solida Sinica 1998年第4期11卷 318-328页

作者： ling, l zeng, QD Guangdong Univ Technol Dept Mechatron Engn Guangzhou 510643 Peoples R China S China Univ Technol Dept Engn Mech Canton 510641 Peoples R China

A modified shear-lag model accounting for the effect of the tensile stiffness of the ma, trix is proposed for solving the stress redistribution due to the failure of fibers and matrix in unidirectionally fibre-reinforced composites. The advantages of this model are simple, reasonable and accurate by comparison with the other similar modified shear-lag models. It can be further extended to study the stress redistribution with interfacial damage between fibres and matrix This paper quantitatively dis cusses the influence of the tensile stiffness ratio of matrix to fibre and of the fibre volume fraction on the stress concentration in the fibres and ma trix adjacent to cut fibres and matrix, and suggests that the influence of the matrix stiffness on the stress concentration can be neglected when the matrix stiffness is low, such as polymer matrix composites, and the fibre volume fraction is high. For other cases such as ceramic and metal matrix composites, the tensile load of the matrix cannot be neglected in the shear-lag analysis.

关键词： unidirectional composites stress concentration matrix stiffness shear-lag analysis

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Projection-domain iteration to estimate unreliable measurements

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Visual Computing for Industry,Biomedicine,and Art 2020年第1期3卷 168-178页

作者： Gengsheng l.zeng Department of radiology and Imaging Sciences University of Utah729 Arapeen DriveSalt Lake CityUT 84108USA Department of Computer Science Utah Valley University800 West University ParkwayOremUT 84058USA

Due to the beam-hardening effect of the broad energy spectrum of the X-ray source in computed tomography,the reconstructed images usually suffer from severe artifacts when metallic objects are being *** artifact correction methods are usually sophisticated and not practical,especially in some non-medical applications,in which the linear attenuation coefficients are *** paper suggests a simple and effective algorithm to estimate the unreliable *** proposed algorithm is an iterative algorithm,in which the iteration is performed in the projection domain,while the objective function is set up in the image *** final image is reconstructed with the conventional filtered backprojection *** feasibility of the proposed method is verified with airport bags that contain some unknown metals.

关键词： Computed tomography artifacts Metal artifact reduction Beam-hardening effects X-ray computed tomography

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Sparse-view tomography via displacement function interpolation

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Visual Computing for Industry,Biomedicine,and Art 2019年第1期2卷 109-118页

作者： Gengsheng l.zeng Department of Engineering Utah Valley University800 West University ParkwayOremUT 84058USA Department of radiology and Imaging Sciences University of Utah729 Arapeen DriveSalt Lake CityUT 84108USA

Sparse-view tomography has many applications such as in low-dose computed tomography(CT).Using undersampled data,a perfect image is not *** goal of this paper is to obtain a tomographic image that is better than the naïve filtered backprojection(FBP)reconstruction that uses linear interpolation to complete the *** paper proposes a method to estimate the un-measured projections by displacement function *** function estimation is a non-linear procedure and the linear interpolation is performed on the displacement function(instead of,on the sinogram itself).As a result,the estimated measurements are not the linear transformation of the measured *** proposed method is compared with the linear interpolation methods,and the proposed method shows superior performance.

关键词： limited data imaging Tomography Estimation

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