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1

The influence of loading rate on the mechanical behavior and energy evolution characteristics of hard and soft rock under triaxial compression

Deng Jihui, Chen Chao, Wu Xiaoning

Journal of Theoretical and Applied Mechanics

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2022

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Vol. 60 nr 3

495--508

EN

To investigate the influence of loading rate and confining pressure on the mechanical behavior and energy evolution characteristics of hard and soft rock, high strength sandstone and low strength granite were subjected to triaxial compression tests with different loading rates. The results show that significant differences exist in the stress-strain curves for sandstone and granite. The confining pressure has a significant effect on the stress-strain curve, while the loading rate has a smaller effect on the stress-strain curve. As the confining pressure increases, the peak axial strain, peak axial stress, total energy, elastic energy and dissipated energy of sandstone and granite increase, the proportion of dissipated energy to total energy of sandstone and the proportion of elastic energy to total energy of granite are reduced. As the loading rate goes up, the peak axial stress, total energy and elastic energy increase in both sandstone and granite. The ultimate failure pattern of sandstone is a typical single inclined plane shear failure, while the ultimate failure pattern of granite consists of a single inclined plane shear failure and a vertical split failure. The loading rate has no significant effect on the macroscopic failure pattern, the elastic and dissipated energies are proportional to the total energy of sandstone and granite.

2

Experimental investigation of the novel dieless clinching process free of blank holder

Qin Denglin, Chen Chao, Zhang Huiyang, Ren Xiaoqiang, Wu Jinliang

Archives of Civil and Mechanical Engineering

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2022

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Vol. 22, no. 1

art. no. e28, 2022

EN

A novel dieless clinching process free of blank holder was proposed in this study. This novel clinching process applied to joining Al5052 sheets under the forming forces from 24 to 54 kN was investigated experimentally. The joint geometrical characteristics, static mechanical strength, energy absorption and failure modes were revealed. From the results, the sound joints can be produced under various forming forces from 24 to 54 kN. With the forming force increasing, the neck thickness was increased continually while the interlock value remained almost constant. On the other hand, the protrusion height of clinched joint was reduced continually with the forming force increasing. Both the tensile strength and shear strength were enhanced with the forming force increasing. Under the forming force of 54 kN, the tensile strength and the shear strength were 1249 and 1107 kN, respectively. In general, a larger joining force leads to a better clinched joint with lower protrusion height and higher mechanical strength.

3

Finite beam element with 22 DOF for curved composite box girders considering torsion, distortion, and biaxial slip

Zhu Li, Wang Jia-Ji, Li Ming-Jie, Chen Chao, Wang Guang-Ming

Archives of Civil and Mechanical Engineering

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2020

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Vol. 20, no. 4

16--34

EN

Experimental and numerical study on the mechanical performance of curved steel–concrete composite box girders is reported in this research. First, this research establishes a theoretical model for curved composite girders with 11° of freedoms (DOFs) for each node. The DOFs include the longitudinal displacement, transverse displacement, deflection, torsion angle, warping angle, and interface biaxial slip between steel and concrete. Based on the virtual work theorem, the equilibrium function, the stiffness matrix, the node displacement matrix and the external load matrix are proposed for the curved composite girders using the FE spatial discretization. Second, the authors conduct an experimental program on three large-scale curved composite girders with various interface shear connectors and central angles. The comparison between the developed finite beam element, the elaborate FE model and the test results indicates the developed finite beam element has an adequate level of accuracy in predicting the deflection, the torsion angle and the axial strain distribution of test specimens. Third, based on the developed finite beam element model, the effect of initial curvature, number of diaphragms, and the interface connector stiffness on the curved composite girder is examined. The simulation results showed that the initial curvature significantly contributes to the displacement and stress of composite girders. Applying more diaphragms can notably reduce the distortion angle and distortion displacement. The interface shear connector stiffness has a significant influence on the curved composite girder. With the increasing shear connector stiffness, the displacement and stress of curved composite girders decrease notably. Based on the parametric analyses, it is recommended to limit the central angle of simply supported composite girder below 45°, to apply an adequate number of diaphragms, and to design curved composite girders as fully shear connection specimens.

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Feasibility study on preparation of magnesium titanate in carbonthermic reduction of vanadium titanomagnetite concentrates

Chen Chao, Sun Ti-Chang, Kou Jue, Wang Xiao-Ping, Zhao Yong-Qiang

Physicochemical Problems of Mineral Processing

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2019

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Vol. 55, iss. 2

417--425

EN

Effect of temperature and Mg:Ti ratio on phase composition and microstructure of reduced pellets was investigated to verify the feasibility of preparation of magnesium titanate by adding MgO in carbonthermic reduction of the vanadium titanomagnetite concentrates (VTC). Thermodynamic analysis results showed that magnesium titanate is more easily generated than FeTi2O5 or TiO2 by the reaction of FeTiO3 and MgO under the reductive atmosphere, which was confirmed by the discovery of magnesium titanate at roast experiment. It was found that the optimum conditions for reduction of VTC pellets were temperature of 1250 ºC and Mg:Ti ratio of 2, and the main phases of reduction product were metallic Fe and magnesium titanate (Mg2TiO4). However, trace iron impurities in Mg2TiO4 particles were found by energy-dispersive spectroscopy (EDS), so further purification is required.

5

Structural and electrical properties of Nb-doped Bi7Ti4.5W0.5O21 intergrowth piezoelectric ceramics

Zhuang Junsheng, Jiang Xiangping, Chen Chao, Jiang Xingan, Huang Xiaokun, Nie Xin, Jiang Yujian

Materiały Ceramiczne

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2019

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T. 71, nr 4

341--349

EN

New layer-structured lead-free piezoelectric ceramics Bi7Ti4.5-xW0.5NbxO21 (BTW-BIT-xNb) (0.00 ≤ x ≤ 0.50) with high Curie temperature TC (up to 690 ℃) have great potential for high temperature applications. However, this material system receives far less attention by researchers due to its poor piezoelectric performance. In the present study, the crystal structure, microstructure and electrical properties of samples with different content of Nb were studied detailedly. The structural characterization by XRD patterns Rietveld refinements and Raman scattering analysis shows that Nb5+ substituted for B-site Ti4+ ion located in the pseudo perovskite blocks and enhanced the orthorhombic distortion, leading to the increasing Curie temperature in the range of 692-762 ℃. The substitution of Nb5+ for Ti4+ acts as donor doping, which effectually reduces the amount of oxygen vacancies, and consequently lowers dielectric loss tgδ. The piezoelectric properties of Nb-doped samples were improved with a maximum piezoelectric constant d33 of 14.3 pC/N obtained in BTW-BIT-0.05Nb sample, which is approximately double that of pure BTW-BIT (~7.3 pC/N). Above results reveal that Nb doped BTW-BIT ceramic system overcomes the difficult coordination between piezoelectric performances and Curie temperature, and realizes the common enhancement of piezoelectric performances and Curie temperature, which is of great value for promoting the practical application of high-temperature piezoelectric ceramics

PL

Nowa bezołowiowa ceramika piezoelektryczna o strukturze warstwowej Bi7Ti4,5-xW0,5NbxO21 (BTW-BIT-xNb) (0,00 ≤ x ≤ 0,50) z wysoką temperaturą Curie TC (do 690 ℃) ma ogromny potencjał do zastosowań w wysokich temperaturach. Jednak ten system materiałowy cieszy się znacznie mniejszym zainteresowaniem ze względu na słabą wydajność piezoelektryczną. W niniejszym badaniu szczegółowo zbadano strukturę krystaliczną, mikrostrukturę i właściwości elektryczne próbek o różnej zawartości Nb. Charakterystyka strukturalna za pomocą analizy Rietvelda dyfraktogramów rentgenowskich i analiza rozpraszania Ramana pokazują, że Nb5+ zastąpił jon Ti4+ w miejscu B znajdujący się w blokach pseudoperowskitu i zwiększył zniekształcenie rombowe, prowadząc do wzrostu temperatury Curie w zakresie 692-762 ℃. Zastąpienie Ti4+ przez Nb5+ działa jak domieszkowanie donorowe, co skutecznie zmniejsza ilość wakancji tlenowych, a tym samym obniża straty dielektryczne tanδ. Właściwości piezoelektryczne próbek domieszkowanych Nb zostały poprawione dzięki maksymalnej stałej piezoelektrycznej d33 wynoszącej 14,3 pC/N, uzyskanej w próbce BTW-BIT-0,05Nb, która jest w przybliżeniu dwukrotnie większa niż czystej BTW-BIT (~7,3 pC/N). Powyższe wyniki pokazują, że system ceramiczny BTW-BIT z domieszką Nb przezwycięża trudne koordynowanie wydajności piezoelektrycznej z temperaturą Curie i realizuje równoczesne polepszenie właściwości piezoelektrycznych i temperatury Curie, co ma wielkie znaczenie dla promowania praktycznego zastosowania wysokotemperaturowej ceramiki piezoelektrycznej