Oct 2024, Volume 31 Issue 7
    

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  • Xu-jie Chen, Qiao-ling Xing, Xuan Tang, Yong Cai, Ming Zhang

    In practical applications, noble metal doping is often used to prepare high performance gas sensors, but more noble metal doping will lead to higher preparation costs. In this study, CeO2/ZnO-Pd with low palladium content was prepared by ultrasonic method with fast response and high selectivity for acetone sensing. With the same amount of palladium added, the selectivity coefficient of CeO2/ZnO-Pd is 1.88 times higher than that of the stirred sensor. Compared with the pure PdO-doped CeO2/ZnO-PdO material, the content of Pd in CeO2/ZnO-PdO is about 30% of that in CeO2/ZnO-PdO, but the selectivity coefficient for acetone is 2.56 times higher. The CeO2/ZnO-Pd sensor has a higher response (22.54) to 50×10−6 acetone at 300 °C and the selectivity coefficient is 2.57 times that of the CeO2/ZnO sensor. The sensor has a sub-second response time (0.6 s) and still has a 2.36 response to 330×10−9 of acetone. Ultrasonic doping makes Pd particles smaller and increases the contact area with gas. Meanwhile, the composition of n-p-n heterojunction and the synergistic effect of Pd/PdO improve the sensor performance. It shows that ultrasonic Pd doping provides a way to improve the utilization rate of doped metals and prepare highly selective gas sensors.

  • Fei-peng Yang, Tao Wen, Lei Zhang, Jian-ying Wang, Shi-long Huang, Shou-xun Ji, Hai-lin Yang

    In this study, the effect of inclination angles relative to the building direction in the additively manufactured eutectic Al-5Mg-2Si alloy was investigated through the laser powder bed fusion (LPBF). The microstructures and mechanical properties of the Al-5Mg-2Si alloy manufactured with different inclination angles (0°, 30°, 45°, 60° and 90°) were reported and discussed. It is found that the “semicircular” melt pool (MP) in the load bearing face of 0° sample was eventually transformed into “stripe-like” MP in the 90° sample, accompanied by an increased fraction of melt pool boundaries (MPBs). Moreover, the microstructural analysis revealed that the columnar-to-equiaxed transition (CET) of the α-Al grains and eutectic Mg2Si was completed in the 90° sample, which were significantly refined with the average size of 9.5 µm and 0.44 µm, respectively. It is also found that the 90° sample exhibited good combination of strength and elongation (i. e. yield strength (YS) of 393 MPa, ultimate tensile strength (UTS) of 483 MPa and elongation (El) of 8.1%). The anisotropic mechanical properties were highly associated with the refined microstructures, thermal stress, and density of MPBs. Additionally, the CET driven by inclination angles were attributed to the variation of thermal conditions inside the local MPs.

  • Ke Huang, You-ping Yi, Shi-quan Huang, Hai-lin He, Jie Liu, Hong-en Hua, Yun-jian Tang

    In this study, the cooling rate was manipulated by quenching with water of different temperatures (30, 60 and 100 °C). Surface and internal residual stresses in the quenched 6061 aluminum alloy samples were measured using hole-drilling and crack compliance methods, respectively. Then, the processability of the quenched samples was evaluated at cryogenic temperatures. The mechanical properties of the as-aged samples were assessed, and microstructure evolution was analyzed. The surface residual stresses of samples W30°C, W60°C and W100°C is −178.7, −161.7 and −117.2 MPa, respectively along x-direction, respectively; and −191.2, −172.1 and −126.2 MPa, respectively along y-direction. The sample quenched in boiling water displaying the lowest residual stress (∼34 % and ∼60% reduction in the surface and core). The generation and distribution of quenching residual stress could be attributed to the lattice distortion gradient. Desirable plasticity was also exhibited in the samples with relatively low quenching cooling rates at cryogenic temperatures. The strengthes of the as-aged samples are 291.2 to 270.1 MPa as the quenching water temperature increase from 30 °C to 100 °C. Fine and homogeneous β″ phases were observed in the as-aged sample quenched with boiling water due to the clusters and Guinier-Preston zones (GP zones) premature precipitated during quenching process.

  • Tao Zhang, Zhen-yang Qin, Hai Gong, Yun-xin Wu, Xin Chen

    Wire-arc additive manufacture (WAAM) has great potential for manufacturing of Al-Cu components. However, inferior mechanical properties of WAAM deposited material restrict its industrial application. Inter-layer cold rolling and thermo-mechanical heat treatment (T8) with pre-stretching deformation between solution and aging treatment were adopted in this study. Their effects on hardness, mechanical properties and microstructure were analyzed and compared to the conventional heat treatment (T6). The results show that cold rolling increases the hardness and strengths, which further increase with T8 treatment. The ultimate tensile strength (UTS) of 513 MPa and yield stress (YS) of 413 MPa can be obtained in the inter-layer cold-rolled sample with T8 treatment, which is much higher than that in the as-deposited samples. The cold-rolled samples show higher elongation than that of as-deposited ones due to significant elimination of porosity in cold rolling; while both the T6 and T8 treatments decrease the elongation. The cold rolling and pre-stretching deformation both contribute to the formation of dense and dispersive precipitated θ′ phases, which inhibits the dislocation movement and enhances the strengths; as a result, T8 treatment shows better strengthening effect than the T6 treatment. The strengthening mechanism was analyzed and it was mainly related to work hardening and precipitation strengthening.

  • Shuo Wei, Pei-pei Ma, Long-hui Chen, Jian-shi Yang, Li-hua Zhan, Chun-hui Liu

    The creep strain of conventionally treated 2195 alloy is very low, increasing the difficulty of manufacturing Al-Cu-Li alloy sheet parts by creep age forming. Therefore, finding a solution to improve the creep formability of Al-Cu-Li alloy is vital. A thorough comparison of the effects of cryo-deformation and ambient temperature large pre-deformation (LPD) on the creep ageing response in the 2195 alloy sheet at 160 °C with different stresses has been made. The evolution of dislocations and precipitates during creep ageing of LPD alloys are revealed by X-ray diffraction and transmission electron microscopy. High-quality 2195 alloy sheet largely pre-deformed by 80% without edge-cracking is obtained by cryo-rolling at liquid nitrogen temperature, while severe edge-cracking occurs during room temperature rolling. The creep formability and strength of the 2195 alloy are both enhanced by introducing pre-existing dislocations with a density over 1.4×1015 m−2. At 160 °C and 150 MPa, creep strain and creep-aged strength generally increases by 4–6 times and 30–50 MPa in the LPD sample, respectively, compared to conventional T3 alloy counterpart. The elongation of creep-aged LPD sample is low but remains relevant for application. The high-density dislocations, though existing in the form of dislocation tangles, promote the formation of refined T 1 precipitates with a uniform dispersion.

  • Rajeev Verma, Vijay Kumar, Saurabh Kango, Amindra Khilla, Rajeev Gupta

    The study investigated the application of radiofrequency (RF)-sputtered TiO2 coatings at various temperatures to enhance the hydrophobicity and corrosion resistance of Al6061 alloy. The research aimed to establish a correlation between the coating process and the resulting surface properties. Surface roughness and wettability were quantified with a surface profilometer and goniometer. Additionally, chemical boiling and salt spray corrosion tests were conducted to evaluate any topographical changes during these procedures. The analysis further involved the use of field-emission scanning electron microscopy (FESEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD) techniques to characterize the deposited coatings. The findings indicated that the TiO2 coating applied at 500 °C exhibited the highest water contact angle and superior corrosion resistance compared to other temperatures. Surface characterization confirmed that this specific TiO2 coating at 500 °C effectively delays corrosion due to its hydrophobic behavior, making it durable for industrial applications.

  • Ke-da Jiang, Ze-xin Liao, Ming-yang Chen, Sheng-dan Liu, Jian-guo Tang

    The impact of cooling rate after solution heat treatment on exfoliation corrosion resistance of a Li-containing 7xxx aluminum alloy was investigated by accelerated immersion and electrochemical impedance spectroscopy test, optical microscope, electron backscatter diffraction and scanning transmission electron microscope. With the decrease of cooling rate from 1700 °C/s to 4 °C/s, exfoliation corrosion resistance of the aged specimens decreases with rating changing from EA to EC and the maximum corrosion depth increasing from about 169.4 µm to 632.1 µm. Exfoliation corrosion tends to develop along grain boundaries in the specimens with cooling rates higher than about 31 °C/s and along both grain boundaries and sub-grain boundaries in the specimens with lower cooling rates. The reason has been discussed based on the changes of the microstructure and microchemistry at grain boundaries and sub-grain boundaries due to slow cooling.

  • Saeed Vazirian, Mohammad Moshkbar Bakhshayesh, Ali Farzadi

    One of the challenges for bimetal manufacturing is the joining process. Hence, transient liquid phase (TLP) bonding was performed between 304L stainless steel and Cp-Ti using an Ag-Cu interlayer with a thickness of 75 µm for bonding time of 20, 40, 60, and 90 min. The bonding temperature of 860 °C was considered, which is under the β transus temperature of Cp-Ti. During TLP bonding, various intermetallic compounds (IMCs), including Ti5Cr7Fe17, (Cr, Fe)2Ti, Ti(Cu, Fe), Ti2(Cu, Ag), and Ti2Cu from 304L toward Cp-Ti formed in the joint. Also, on the one side, with the increase in time, further diffusion of elements decreases the blocky IMCs such as Ti5Cr7Fe17, (Cr, Fe)2Ti, Ti(Cu, Fe) in the 304L diffusion-affected zone (DAZ) and reaction zone, and on the other side, Ti2(Cu, Ag) IMC transformed into fine morphology toward Cp-Ti DAZ. The microhardness test also demonstrated that the (Cr, Fe)2Ti + Ti5Cr7Fe17 IMCs in the DAZ on the side of 304L have a hardness value of HV 564, making it the hardest phase. The maximum and minimum shear strength values are equal to 78.84 and 29.0 MPa, respectively. The cleavage pattern dominated fracture surfaces due to the formation of brittle phases in dissimilar joints.

  • Xu-rui Chen, Jun Wu, Li Gu, Xue-bo Cao

    Carbon nanotubes (CNTs) have garnered significant attention in the fields of science, engineering, and medicine due to their numerous advantages. The initial step towards harnessing the potential of CNTs involves their macroscopic assembly. The present study employed a gentle and direct self-assembly technique, wherein controlled growth of CNT sheaths occurred on the metal wire’s surface, followed by etching of the remaining metal to obtain the hollow tubes composed of CNTs. By controlling the growth time and temperature, it is possible to alter the thickness of the CNTs sheath. After immersing in a solution containing 1 g/L of CNTs at 60 °C for 24 h, the resulting CNTs layer achieved a thickness of up to 60 µm. These hollow CNTs tubes with varying inner diameters were prepared through surface reinforcement using polymers and sacrificing metal wires, thereby exhibiting exceptional attributes such as robustness, flexibility, air tightness, and high adsorption capacity that effectively capture CO2 from the gas mixture.

  • Wei-fang Liu, Zi-han Hu, Qi Zhang

    Aqueous zinc ion hybrid capacitors (ZIHCs) are considered one of the most promising electrochemical energy storage systems due to their high safety, environmental friendliness, low cost, and high power density. However, the low energy density and the lack of sustainable design strategies for the cathodes hinder the practical application of ZIHCs. Herein, we design the N and O co-doped porous carbon cathode by annealing metal-organic framework (ZIF-8). ZIF-8 retains the original dodecahedral structure with a high specific surface (2814.67 m2/g) and I G/I D ratio of 1.0 during carbonization and achieves self-doping of N and O heteroatoms. Abundant defect sites are introduced into the porous carbon to provide additional active sites for ion adsorption after the activation of carbonized ZIF-8 by KOH treatment. The ZIHCs assembled with modified ZIF-8 as the cathode and commercial zinc foil as the anode show an energy density of 125 W · h/kg and a power density of 79 W/kg. In addition, this ZIHCs device achieves capacity retention of 77.8% after 9000 electrochemical cycles, which is attributed to the diverse pore structure and plentiful defect sites of ZIF-8-800(KOH). The proposed strategy may be useful in developing high-performance metal-ion hybrid capacitors for large-scale energy storage.

  • Gülşah Güven, Berivan Tunç, Ş. Beste Aydin, Gülay Bulut

    Frothers facilitate the reduction of bubbles size by preventing bubbles coalescence and produce more stable froths. The collision probability of the bubbles and particles substantially increases by decreasing bubble size. For the same volume system, fewer bubbles result from a distribution of large-sized bubbles, and more bubbles result from a distribution of small-sized bubbles. In this research, fundamental two-phase frother characterization parameters were aimed to link with three-phase coal and talc flotation behavior. For this purpose, the effect of single and dual frother systems on inhibiting bubble coalescence was investigated with methyl isobutyl carbinol (MIBC), isooctanol (2 ethyl hexanol), pine oil, and Dowfroth 250. Based on the results of single frothers, isooctanol at the lowest critical coalescence concentration (CCC) value of 6×10−6 achieved the smallest bubbles with Sauter mean diameter of 0.80 mm. By blending Dowfroth 250 and pine oil, the bubbles size decreased significantly, reaching 0.45 mm. While the highest recoveries in coal flotation were obtained in single and frother blends where the bubbles size was measured as the smallest in two-phase system, and such a relationship was not found for talc flotation.

  • Zi-long Zhou, Zhen Wang, Rui-shan Cheng, Xin Cai, Ri-yan Lan

    Water-coupled charge blasting is a promising technique to efficiently break rock masses. In this study, numerical models of double boreholes with water-coupled charge are established using LS-DYNA and are calibrated by the tests of rock masses subjected to explosion loads to examine its performance. The crack levels of rock mass induced by water-coupled charge blasting and air-coupled charge blasting are first compared. It is found that water-coupled charge blasting is more appropriate to fracture deep rock mass than air-coupled charge blasting. In addition, the effects of rock properties, water-coupled charge coefficients, and borehole connection angles on the performance of water-coupled charge blasting are investigated. The results show that rock properties and water-coupled charge coefficients can greatly influence the crack and fragmentation levels of rock mass induced by water-coupled charge blasting under uniform and non-uniform in-situ stresses. However, changing borehole-connection angles can only affect crack and fragmentation levels of rock mass under non-uniform in-situ stresses but barely affect those under uniform in-situ stresses. A formula is finally proposed by considering the above-mentioned factors to provide the design suggestion of water-coupled charge blasting to fracture rock mass with different in-situ stresses.

  • Rui Zhao, Ming Tao, Gong-liang Xiang, Shao-feng Wang, Hua-tao Zhao

    In this study, the dynamic stress concentration factors (DSCF) around a straight-wall arch tunnel (SWAT) were solved analytically utilizing the complex variable function methods and Duhamel’s integral. The effects of wavelength, incident angle, and blasting rising time on the DSCF distribution were analyzed. Theoretical results pointed out dynamic disturbances resulting in compressive stress concentration in the vertical direction and tensile stress in the incident direction. As the wavelength and rising time increased, there was a tendency for the amplitude of stress concentration to initially rise and then converge. Moreover, a series of 3D FEM models were established to evaluate the effect of different initial stress states on the dynamic failure of the tunnel surrounding rock. The results indicated that the failure of the surrounding rock was significantly influenced by the direction of the static maximum principal stress and the direction of the dynamic disturbance. Under the coupling of static and blasting loading, damage around the tunnel was more prone to occur in the dynamic and static stress concentration coincidence zone. Finally, the damage modes of rock tunnel under static stress and blasting disturbance from different directions were summarized and a proposed support system was presented. The results reveal the mechanisms of deep-buried rock tunnel destruction and dynamically triggered rockburst.

  • Liang Li, Jia-jun Chen, Lian-heng Zhao, Ke-pei He, Shi-hong Hu, Hua-long Li

    Blasting-induced cracks in the rock surrounding deeply buried tunnels can result in water gushing and rock mass collapse, posing significant safety risks. However, previous theoretical studies on the range of blasting-induced cracks often ignore the impact of the in-situ stress, especially that of the intermediate principal stress. The particle displacement−crack radius relationship was established in this paper by utilizing the blasthole cavity expansion equation, and theoretical analytical formulas of the stress−displacement relationship and the crack radius were derived with unified strength theory to accurately assess the range of cracks in deep surrounding rock under a blasting load. Parameter analysis showed that the crushing zone size was positively correlated with in-situ stress, intermediate principal stress, and detonation pressure, whereas negatively correlated with Poisson ratio and decoupling coefficient. The dilatancy angle-crushing zone size relationship exhibited nonmonotonic behavior. The relationships in the crushing zone and the fracture zone exhibited opposite trends under the influence of only in-situ stress or intermediate principal stress. As the in-situ stress increased from 0 to 70 MPa, the rate of change in the crack range and the attenuation rate of the peak vibration velocity gradually slowed.

  • Cheng-han Zhang, Hong-guang Ji, Peng Jiang, Shuang You, Qian-cheng Geng, Chen-jiang Jiao

    The macroscopic mechanical properties of rocks are significantly influenced by their microstructure. As a material bonded by mineral grains, the grain morphology of crystalline rock is the primary factor influencing the strength. However, most strength criteria neglect the strength variations caused by different grain characteristics in rocks. Furthermore, the traditional linear criteria tend to overestimate tensile strength and exhibit apex singularity. To address these shortcomings, a piecewise strength criterion that considers the grain size effect has been proposed. A part of an ellipse was employed to construct the envelope of the tensive-shear region on the meridian plane, to accurately reproduce the low tensile-compressive strength ratio. Based on the analysis of experimental data, both linear and exponential modification functions that account for grain size effects were integrated into the proposed criterion. The corresponding finite element algorithm has been implemented. The accuracy and applicability of the proposed criterion were validated by comparing with the experimental data.

  • Chen-chen Feng, Zhi-liang Wang, Jian-guo Wang, Zhi-tang Lu, Song-yu Li

    This paper developed a statistical damage constitutive model for deep rock by considering the effects of external load and thermal treatment temperature based on the distortion energy. The model parameters were determined through the extremum features of stress – strain curve. Subsequently, the model predictions were compared with experimental results of marble samples. It is found that when the treatment temperature rises, the coupling damage evolution curve shows an S-shape and the slope of ascending branch gradually decreases during the coupling damage evolution process. At a constant temperature, confining pressure can suppress the expansion of micro-fractures. As the confining pressure increases the rock exhibits ductility characteristics, and the shape of coupling damage curve changes from an S-shape into a quasi-parabolic shape. This model can well characterize the influence of high temperature on the mechanical properties of deep rock and its brittleness-ductility transition characteristics under confining pressure. Also, it is suitable for sandstone and granite, especially in predicting the pre-peak stage and peak stress of stress – strain curve under the coupling action of confining pressure and high temperature. The relevant results can provide a reference for further research on the constitutive relationship of rock-like materials and their engineering applications.

  • Qiang Zhu, Qian Yin, Zhi-gang Tao, Man-chao He, Bo-wen Zheng, Hong-wen Jing, Shu-lin Ren, Qiang Zhang, Bo Meng, Dong-feng Bai, Sai-sai Wu, Jiang-yu Wu

    A comprehensive understanding of the dynamic frictional characteristics in rock joints under high normal load and strong confinement is essential for ensuring the safety of deep engineering construction and mitigating geological disasters. This study conducted shear experiments on rough rock joints under displacement-controlled dynamic normal loads, investigating the shear behaviors of joints across varying initial normal loads, normal loading frequencies, and normal loading amplitudes. Experimental results showed that the peak/valley shear force values increased with initial normal loads and normal loading frequencies but showed an initial increase followed by a decrease with normal loading amplitudes. Dynamic normal loading can either increase or decrease shear strength, while this study demonstrates that higher frequencies lead to enhanced friction. Increased initial normal loading and normal loading frequency result in a gradual decrease in joint roughness coefficient (JRC) values of joint surfaces after shearing. Positive correlations existed between frictional energy dissipation and peak shear forces, while post-shear joint surface roughness exhibited a negative correlation with peak shear forces through linear regression analysis. This study contributes to a better understanding of the sliding responses and shear mechanical characteristics of rock joints under dynamic disturbances.

  • Dong-qiao Liu, Yun-peng Guo, Kai Ling, Jie-yu Li

    Bedding structural planes significantly influence the mechanical properties and stability of engineering rock masses. This study conducts uniaxial compression tests on layered sandstone with various bedding angles (0°, 15°, 30°, 45°, 60°, 75° and 90°) to explore the impact of bedding angle on the deformational mechanical response, failure mode, and damage evolution processes of rocks. It develops a damage model based on the Logistic equation derived from the modulus’s degradation considering the combined effect of the sandstone bedding dip angle and load. This model is employed to study the damage accumulation state and its evolution within the layered rock mass. This research also introduces a piecewise constitutive model that considers the initial compaction characteristics to simulate the whole deformation process of layered sandstone under uniaxial compression. The results revealed that as the bedding angle increases from 0° to 90°, the uniaxial compressive strength and elastic modulus of layered sandstone significantly decrease, slightly increase, and then decline again. The corresponding failure modes transition from splitting tensile failure to slipping shear failure and back to splitting tensile failure. As indicated by the modulus’s degradation, the damage characteristics can be categorized into four stages: initial no damage, damage initiation, damage acceleration, and damage deceleration termination. The theoretical damage model based on the Logistic equation effectively simulates and predicts the entire damage evolution process. Moreover, the theoretical constitutive model curves closely align with the actual stress – strain curves of layered sandstone under uniaxial compression. The introduced constitutive model is concise, with fewer parameters, a straightforward parameter determination process, and a clear physical interpretation. This study offers valuable insights into the theory of layered rock mechanics and holds implications for ensuring the safety of rock engineering.

  • Ke-yue Zheng, Cheng-hua Shi, Qian-jin Zhao, Ming-feng Lei, Chao-jun Jia, Zhu Peng

    Due to the long-term plate tectonic movements in southwestern China, the in-situ stress field in deep formations is complex. When passing through deep soft-rock mass under non-hydrostatic high in-situ stress field, tunnels will suffer serious asymmetric deformation. There is no available support design method for tunnels under such a situation in existing studies to clarify the support time and support stiffness. This study first analyzed the mechanical behavior of tunnels in non-hydrostatic in-situ stress field and derived the theoretical equations of the ground squeezing curve (GSC) and ground loosening curve (GLC). Then, based on the convergence confinement theory, the support design method of deep soft-rock tunnels under non-hydrostatic high in-situ stress field was established considering both squeezing and loosening pressures. In addition, this method can provide the clear support time and support stiffness of the second layer of initial support. The proposed design method was applied to the Wanhe tunnel of the China-Laos railway in China. Monitoring data indicated that the optimal support scheme had a good effect on controlling the tunnel deformation in non-hydrostatic high in-situ stress field. Field applications showed that the secondary lining could be constructed properly.

  • Ming-xiao Hou, Bing-xiang Huang, Xing-long Zhao, Xue-jie Jiao, Chen-yang Zheng

    Roof disaster has always been an important factor restricting coal mine safety production. Acidic effect can reform the rock mass structure to weaken the macroscopic strength characteristics, which is an effective way to control the hard limestone roof. In this study, the effects of various factors on the reaction characteristics and mechanical properties of limestone were analyzed. The results show that the acid with stronger hydrogen production capacity after ionization (pK a<0) has more prominent damage to the mineral grains of limestone. When pK a increases from −8.00 to 15.70, uniaxial compressive strength and elastic modulus of limestone increase by 117.22% and 75.98%. The influence of acid concentration is manifested in the dissolution behavior of mineral crystals, the crystal defects caused by large-scale acid action will lead to the deterioration of limestone strength, and the strength after 15% concentration reformation can be reduced by 59.42%. The effect of acidification time on limestone has stages and is the most obvious in the initial metathesis reaction stage (within 60 min). The key to the strength damage of acidified limestone is the participation of hydrogen ions in the reaction system. Based on the analytic hierarchy process method, the influence weights of acid type, acid concentration and acidification time on strength are 24.30%, 59.54% and 16.16%, respectively. The research results provide theoretical support for the acidification control of hard limestone roofs in coal mines.

  • Bei Jiang, Ming-zi Wang, Qi Wang, Zhong-xin Xin, Xue-yang Xing, Yu-song Deng, Liang-di Yao

    Non-pillar mining technology with automatically formed roadway is a new mining method without coal pillar reservation and roadway excavation. The stability control of automatically formed roadway is the key to the successful application of the new method. In order to realize the stability control of the roadway surrounding rock, the mechanical model of the roof and rib support structure is established, and the influence mechanism of the automatically formed roadway parameters on the compound force is revealed. On this basis, the roof and rib support structure technology of confined lightweight concrete is proposed, and its mechanical tests under different eccentricity are carried out. The results show that the bearing capacity of confined lightweight concrete specimens is basically the same as that of ordinary confined concrete specimens. The bearing capacity of confined lightweight concrete specimens under different eccentricities is 1.95 times higher than those of U-shaped steel specimens. By comparing the test results with the theoretical calculated results of the confined concrete, the calculation method of the bearing capacity for the confined lightweight concrete structure is selected. The design method of confined lightweight concrete support structure is established, and is successfully applied in the extra-large mine, Ningtiaota Coal Mine, China.

  • Heng-zhong Zhu, Lei Xu, Zhi-jie Wen

    This study is the result of long-term efforts of the authors’ team to assess ground response of gob-side entry by roof cutting (GSERC) with hard main roof, aiming at scientific control for GSERC deformation. A comprehensive field measurement program was conducted to determine entry deformation, roof fracture zone, and anchor bolt (cable) loading. The results indicate that GSERC deformation presents asymmetric characteristics. The maximum convergence near roof cutting side is 458 mm during the primary use process and 1120 mm during the secondary reuse process. The entry deformation is closely associated with the primary development stage, primary use stage, and secondary reuse stage. The key block movement of roof cutting structure, a complex stress environment, and a mismatch in the supporting design scheme are the failure mechanism of GSERC. A controlling ideology for mining states, including regional and stage divisions, was proposed. Both dynamic and permanent support schemes have been implemented in the field. Engineering practice results indicate that the new support scheme can efficiently ensure long-term entry safety and could be a reliable approach for other engineering practices.

  • Duo-jia Shi, Cai-you Zhao, Xin-hao Zhang, Jun-yuan Zheng, Na-chao Wei, Ping Wang

    The problems associated with vibrations of viaducts and low-frequency structural noise radiation caused by train excitation continue to increase in importance. A new floating-slab track vibration isolator-non-obstructive particle damping-phononic crystal vibration isolator is proposed herein, which uses the particle damping vibration absorption technology and bandgap vibration control theory. The vibration reduction performance of the NOPD-PCVI was analyzed from the perspective of vibration control. The paper explores the structure-borne noise reduction performance of the NOPD-PCVIs installed on different bridge structures under varying service conditions encountered in practical engineering applications. The load transferred to the bridge is obtained from a coupled train-FST-bridge analytical model considering the different structural parameters of bridges. The vibration responses are obtained using the finite element method, while the structural noise radiation is simulated using the frequency-domain boundary element method. Using the particle swarm optimization algorithm, the parameters of the NOPD-PCVI are optimized so that its frequency bandgap matches the dominant bridge structural noise frequency range. The noise reduction performance of the NOPD-PCVIs is compared to the steel-spring isolation under different service conditions.

  • Jian-feng Mao, Dao-hang Li, Zhi-wu Yu, Wen-feng Cai, Wei Guo, Guang-wen Zhang

    Running safety assessment and tracking irregularity parametric sensitivity analysis of high-speed maglev train-bridge system are of great concern, especially need perfect refinement models in which all properties can be well characterized based on various stochastic excitations. A three-dimensional refined spatial random vibration analysis model of high-speed maglev train-bridge coupled system is established in this paper, in which multi-source uncertainty excitation can be considered simultaneously, and the probability density evolution method (PDEM) is adopted to reveal the system-specific uncertainty dynamic characteristic. The motion equation of the maglev vehicle model is composed of multi-rigid bodies with a total 210-degrees of freedom for each vehicle, and a refined electromagnetic force-air gap model is used to account for the interaction and coupling effect between the moving train and track beam bridges, which are directly established by using finite element method. The model is proven to be applicable by comparing with Monte Carlo simulation. By applying the proposed stochastic framework to the high maglev line, the random dynamic responses of maglev vehicles running on the bridges are studied for running safety and stability assessment. Moreover, the effects of track irregularity wavelength range under different amplitude and running speeds on the coupled system are investigated. The results show that the augmentation of train speed will move backward the sensitive wavelength interval, and track irregularity amplitude influences the response remarkably in the sensitive interval.