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Electrical and Piezoresistive Properties of Steel Fiber Cement-based Composites Aligned by a Magnetic Field

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Journal of Wuhan University of Technology(materials Science) 2022年第2期37卷 229-240页

作者：刘力源徐金霞 WANG Yang YIN Tianjiao CHU Hongqiang College of Mechanics and Materials Hohai UniversityNanjing 211100China

Directionally distributed steel fiber cement-based composites(SFCCs)were prepared by magnetic field(MF)induction technology.The orientation factor of steel fibers in the as-obtained SFCCs was determined.Besides,the electrical resistivity and piezoresistive responses in two directions of aligned steel fiber cement-based composites,i e,parallel and perpendicular to MF,were measured.The effects of several variables,eg,steel fiber content,curing age,humidity,and temperature,on anisotropic electrical property were studied.The cyclic and failure piezoresistive responses in different directions were tested.It is found that the aligned steel fibers in the as-obtained SFCCs have a high orientation factor more than 0.88.Besides,SFCCs with aligned steel fibers exhibit an obvious anisotropic conductivity and piezoelectric sensitivity.The electrical conductivity of SFCCs with aligned steel fibers is less affected by temperature and humidity.At the steel fiber content of 2.5wt%,the piezoelectric sensitivity coefficient of SFCCs in the direction parallel to MF has the highest value of 324.14.In addition,the piezoresistive properties of SFCCs with aligned steel fibers in the direction parallel to MF indicate excellent sensitivity and stability under cyclic loading and monotonic loading.

关键词： electrical resistivity aligned steel fiber piezoresistivity cement-based composites

Evaluation of Corrosion Inhibition of NO_(2)^(-) Intercalated LDHs on Steel Coated by Cement Paste

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Journal of Wuhan University of Technology(materials Science) 2022年第3期37卷 399-409页

作者：吴悠徐金霞 MEI Youjin College of Mechanics and Materials Hohai UniversityNanjing 210098China

The purpose of this study is to apply the steel coated by cement paste to evaluate the corrosion inhibition of NO_(2)^(-) intercalated Mg-Al layered double hydroxides(LDHs),which was prepared by a conventional calcination-rehydration method.The chloride equilibrium isotherm,open-circuit potential(OCP)and electrochemical impedance spectroscopy(EIS)of steel in the saturated Ca(OH)_(2) solution contaminated by chloride ions were measured.The microstructures of as-obtained LDHs and cement paste containing the LDHs were observed by scanning electron microscope(SEM),X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FT-IR)and mercury intrusion porosimetry(MIP).It is found that the technique using the steel coated by the cement paste layer containing the LDHs to represent the steel in real concrete can be applied to accurately evaluate the corrosion inhibition performance of NO_(2)^(-) intercalated LDHs in a short duration.The addition of NO_(2)^(-) intercalated Mg-Al LDHs can improve the absorption capacity of Cl^(-) and the anti-corrosion property of cement paste layer.The combination actions of the refinement of pore structure,uptake of chloride ions and release of inhibitive NO_(2)^(-) contribute to the better corrosion protection property of cement paste layer.Moreover,a schematic mechanism of chloride intrusion for the steel specimen with cement paste layer is developed.

关键词： layered double hydroxides cement paste layer chloride equilibrium isotherm anticorrosion property

Characterization and in-situ formation mechanism of tungsten carbide reinforced Fe-based alloy coating by plasma cladding

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International Journal of Minerals,Metallurgy and materials 2018年第4期25卷 439-443页

作者： Mi-qi Wang Ze-hua Zhou Lin-tao Wu Ying Ding Ze-hua Wang College of Mechanics and Materials Hohai University

The precursor carbonization method was first applied to prepare W–C compound powder to perform the in-situ synthesis of the WC phase in a Fe-based alloy coating. The in-situ formation mechanism during the cladding process is discussed in detail. The results reveal that fine and obtuse WC particles were successfully generated and distributed in Fe-based alloy coating via Fe/W–C compound powders. The WC particles were either surrounded by or were semi-enclosed in blocky M7C3 carbides. Moreover, net-like structures were confirmed as mixtures of M23C6 and α-Fe; these structures were transformed from M7C3. The coarse herringbone M6C carbides did not only derive from the decomposition of M7C3 but also partly originated from the chemical reaction at the α-Fe/M23C6 interface. During the cladding process, the phase evolution of the precipitated carbides was WC → M7C3 → M23C6 ＋ M6C.

关键词： precursor carbonization tungsten carbide （WC） microstructure in-situ formation mechanism phase evolution

Bond-associated non-ordinary state-based peridynamic model for multiple spalling simulation of concrete

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Acta Mechanica Sinica 2021年第7期37卷 1104-1135,I0002页

作者： Siyang Yang Xin Gu Qing Zhang Xiaozhou Xia Department of Engineering mechanics College of Mechanics and MaterialsHohai UniversityNanjing 211100China

The non-ordinary state-based peridynamic(NOSB PD)model has the capability of incorporating existing constitutive relationships in the classical continuum mechanics.In the present work,we first develop an NOSB PD model corresponding to the Johnson–Holmquist II(JH-2)constitutive damage model,which can describe the severe damage of concrete under intense impact compression.Besides,the numerical oscillation problem of the NOSB PD caused by zero-energy mode is analyzed and hence a bond-associated non-ordinary state-based peridynamic(BA-NOSB PD)model is adopted to remove the oscillation.Then,the elastic deformation of a three-dimensional bar is analyzed to verify the capability of BA-NOSB PD in eliminating the numerical oscillation.Furthermore,concrete spalling caused by the interaction of incident compression wave and reflected tension wave is simulated.The dynamic tensile fracture process of concrete multiple spalling is accurately reproduced for several examples according to the spalling number and spalling thickness analysis,illustrating the approach can well simulate and analyze the concrete spalling discontinuities.

关键词： Non-ordinary state-based peridynamics Bond-associated horizon-Johnson-HolmquistⅡ(JH-2)model Wave propagation Multiple spalling

Is Mg_(17)Al_(12) ductile or brittle?A theoretical insight

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Journal of Magnesium and Alloys 2023年第3期11卷 936-944页

作者： Jiajia Wang Lei Niu Yanglin Zhang Jianqing Chen Jinghua Jiang Dan Song Baosong Li Guobing Ying Jiangbo Cheng Aibin Ma College of Mechanics and Materials Hohai UniversityNanjing 210098P.R.of China

The Mg_(17)Al_(12)-phase,which is common and important in Mg-Al alloy,has long been regarded as a brittle phase in experiments but theoretical calculations report controversial results.To unravel why theoretical calculations report controversial results and determine whether Mg_(17)Al_(12)is brittle or ductile,density functional theory calculations on atomic level are performed to investigate mechanic properties of Mg_(17)Al_(12)without containing alloying elements and without taking the size effect.The results showed that the parameter k-point played critical role in the DFT-based elastic calculations.The convergent G/B ratio of Mg_(17)Al_(12)was about 0.52,suggesting that the Mg_(17)Al_(12)-phase was theoretically ductile although its ductility was poor.The chemical bonding in Mg_(17)Al_(12)was the mixture of metallic Mg-Mg bond and covalent Al-Al bond.The advantage of metallic bonding over covalent bonding provided a possible explanation for the ductility of Mg_(17)Al_(12).Possible reasons for the brittleness of Mg_(17)Al_(12)in experiments are also discussed.

关键词： Mg_(17)Al_(12) Ductile Brittle DFT Elastic properties

Barrier or easy-flow channel: The role of grain boundary acting on vortex motion in type-Ⅱ superconductors

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Chinese Physics B 2021年第9期30卷 499-505页

作者：刘宇苟晓凡薛峰 College of Mechanics and Materials Hohai UniversityNanjing 211100China

Grain boundaries(GBs),as extremely anisotropic pinning defects,have a strong impact on vortex motion in type-Ⅱsuperconductors,and further on the macro level dominates the superconductivity for example the critical current density.Many previous studies indicated that mostly GB plays the role of a strong barrier for vortex motion,while an easy-flow channel just under some certain conditions.In order to thoroughly make clear of the questions of what is exactly the role of GB on vortex motion and how it works,in this article we developed a large scale molecular dynamic model and revealed the action of GB on vortex motion in type-Ⅱsuperconductors.The most significant finding is that the role of GB on vortex motion can be changeable from a barrier to an easy-flow channel,and which is intrinsically determined by the competition effect correlated with its action on vortex between in the GB and no-GB regions.Such the competition effect essentially depends on the attributes of both the GB(described by the GB strength and angleθ)and no-GB pining regions(by the relative disorder strengthα_(p)/α_(v)).Specifically,for a YBa_(2)Cu_(3)O_(7-x)(YBCO)sample,to obtain a clear knowledge of vortex motion in GB region,we visualized the three typical trajectories of vortices during the three vortex movement stages.Further,in order to understand how GB results in the macro current-carrying property,corresponding to the current-voltage relation of the YBCO conductor,we obtained the average velocity v_(y) of vortices varying with their driving force,which is nearly identical with the previous observations.

关键词： type-II superconductors grain boundary(GB) vortex motion competition effect GB strength the relative disorder strengthαp/αv

Analytic calculation of magnetic force between two current-carrying coils

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Applied Mathematics and mechanics(English Edition) 2015年第4期36卷 475-486页

作者： Xiaofan GOU Jian QIN College of Mechanics and Materials Hohai University

Current-carrying coils are basic elements in electromagnetic equipments, for example, in high field magnets from high temperature superconducting wires or tapes. In the assembly of these systems and their current-carrying operation, unavoidable mis- alignment and shift from the original position can be induced by disturbances such as the imbalance of magnetic force due to safety problems. For two current-carrying coils with non-coplanar axes, the analytic expression of the magnetic force between the two coils is presented according to the rule of Ampere circulation and the Biot-Savart law. Based on the expression, the dependence of the magnetic force on the size and the relative position of each other is further investigated, and the variation of the magnetic force is obtained with the above parameters.

关键词： current-carrying coil non-coplanar axis magnetic force analytic calcula-tion

Microstructure and properties of in-situ synthesized Cu-1 wt%TiC alloy followed by ECAP and post-annealing

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Progress in Natural Science:materials International 2016年第6期26卷 643-649页

作者： Shizhan Ni Jinghua Jiang Jianqing Chen Dan Song Aibin Ma College of Mechanics and Materials Hohai University

A dispersion-strengthened copper alloy with 1 wt% TiC for commercial electrical-contact wires was prepared by in-situ reaction casting, grain-ultrafining by equal-channel angular pressing(ECAP) and subsequent annealing with aim to obtain excellent comprehensive performance. The results showed that fine TiC particles were in-situ synthesized in the as-cast Cu matrix and aggregated in clusters, and thus mechanical properties of the as-cast alloy deemed insufficient. Continued ECAP at 473 K significantly refined the grains of the as-cast alloy and improved the distribution of TiC particles. Due to multiple strengthening mechanisms, the ECAP-processed alloys maintained good conductivity with obviously enhanced tensile strength and hardness values. After postECAP annealing, the elongation and conductivity of the fine-grained copper alloy increased with the adequate tensile strength. The novel combined process endows the alloy appropriate performance to serve current highfrequency electrification railway systems.

关键词： Cu-1 wt%TiC alloy In-situ reaction Dispersion strengthen Equal channel angular pressing Annealing Mechanical properties Conductivity

A Modified Lattice Model of the Reversible Effect of Axial Strain on the Critical Current of Polycrystalline REBa2Cu3O7-δ Films

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Chinese Physics Letters 2015年第3期32卷 128-132页

作者：苟晓凡朱光 College of Mechanics and Materials Hohai University

The strain effect on the critical current is one of the most important properties for polycrystalline YBa2 Cu3O7-δ （REBCO, RE： rare earth） films, in which the reversible effect is intrinsic in the range of strain 0 and the irreversible strain εirr. By introducing the applied strain, a modified grain boundaries （GBs） in the REBCO film is developed. lattice model combining the strain and misorientation of A good agreement of the calculation on the lattice model with the experimental data shows that the lattice model is able to well describe the reversible effect of axial strain on the critical current of the REBCO film, and provides a good understanding of the mechanism of the reversible effect of the strain. Moreover, the effects of the crystallographic texture of the REBCO film and the residual strain εr on the variation of the critical current with the applied strain are extensively investigated. Furthermore by using the developed lattice model, the irreversible strain εirr of the REBCO film can be theoretically determined by comparing the calculation of the critical current-strain curve with the experimental data.

关键词： REBCO A Modified Lattice Model of the Reversible Effect of Axial Strain on the Critical Current of Polycrystalline REBa2Cu3O Films Cu