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TAN Keyu, CHEN Baitong, HUO Zongze, ZHANG Pengyan, WANG Zhiyong*
2025,40(2):143-149 ,DOI: 10.7520/1001-4888-24-052
Abstract:
Metamaterials are a current research hotspot in the terahertz (THz) field. To address the high manufacturing costs of existing strain sensors composed of metamaterial structures, this paper proposes a periodic circular hole array structure. The strain sensing mechanism based on this structure was investigated through experimental methods and numerical simulations. The THz transmission spectrum of the periodic circular hole array structure was measured under no load conditions. Furthermore, the effect of strain on the THz transmission spectrum of this structure was explored through loading experiments. Simulations of mechanics-electromagnetics coupling were conducted to simulate the modulation effect of strain on the THz transmission spectrum of the periodic circular hole array structure, thereby validating the experimental results. Both experimental and simulation results consistently demonstrate that the periodic circular hole array structure can modulate THz waves, resulting in a characteristic absorption valley in the THz transmission spectrum. When the THz waves are linearly polarized and the loading direction is parallel to the polarization direction, the strain can modulate the horizontal position of the characteristic absorption valley, causing a regular frequency shift. This paper establishes a linear relationship between strain and the frequency shift of the characteristic absorption valley, enabling strain sensing. Utilizing this periodic circular hole array structure, a cost-effective strain sensor with excellent strain sensing performance can be designed.
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ZHOU Gaowei, HOU Yu*, ZHAO Zhixiang, WANG Xi
2025,40(2):150-162 ,DOI: 10.7520/1001-4888-24-064
Abstract:
The friction torque inside the rolling bearing will intensify the friction wear and fatigue peeling of the contact surface between the rolling element and the raceway. This article is based on the line tension method and develops an improved line tension method suitable for measuring the friction torque of rolling bearings under large radial loads. The method solves the contradiction between large radial loading and high-precision testing of friction moment by connecting multiple pairs of force sensors in parallel. Using cylindrical roller bearings as experimental bearings, a special sensor was applied to the bearing seat, and a set of experimental systems was designed and constructed to discuss the practicality and effectiveness of this testing method. Finally, an analysis and study were conducted on the influence of different shaft speeds, external loads, and types of lubricating grease on the friction torque. The results showed that under most operating conditions, the friction torque of cylindrical roller bearings increases with the increase of external loads, shaft speeds, and lubricating oil viscosity. However, under slipping conditions, the slip rate becomes the dominant factor affecting the friction torque.
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PENG Qingyue, WANG Kun, NI Ke, WANG Zhengzhi*
2025,40(2):163-171 ,DOI: 10.7520/1001-4888-24-047
Abstract:
Photopolymerizable resins are commonly used in various fields, including 3D printing, surface coatings, and dental restorations, due to their simple reaction conditions and ease of use. However, the shrinkage stresses that occur within the material and at the substrate interface during the polymerization process can significantly impact the performance of photopolymerized resins. Therefore, it is crucial to accurately measure the shrinkage stress in these resins to enhance their performance. Existing testing methods for the shrinkage stress are limited in the uniaxial or axisymmetric conditions, which makes it challenging to test three-dimensional stresses in practical applications. The correlation between the counts of acoustic emission events and the mean stress predicted by the finite element model was demonstrated, which validated the reliability of the numerical model established in this work. Furthermore, the stress distribution within the resin and on the resin-substrate interface was accurately predicted by the numerical model. It is shown that the mass fraction of inorganic filler affects the three-dimensional shrinkage stress during the curing process of photopolymerization resins, which is related to external stiffness. Enhancing the filler mass fraction can significantly reduce resin shrinkage stress when the environmental stiffness is low. However, in conditions of high stiffness, the impact of filler mass fraction on resin shrinkage stress is marginal. The integration of acoustic emission testing and finite element analysis provides a new approach to evaluating the three-dimensional shrinkage stress of photopolymerized materials. These test findings can provide valuable insights for improving processing methods and increasing material productivity.
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WANG Lei*, HUANG Yifeng, WANG Zixia, ZHANG Wei
2025,40(2):172-182 ,DOI: 10.7520/1001-4888-24-102
Abstract:
Double-L-shaped high-rise building is a new form of high-rise building, this type of building has many facades and relatively complex wind loads, however, the related research is very scarce. Therefore, a series of numerical simulations and wind tunnel tests were conducted to systematically investigate the shape coefficient and wind force coefficient of double L-shaped high-rise buildings, and the influences of wind direction, L-angle, aspect ratio, and thickness ratio on wind loads were analyzed in this work. Meanwhile, the shape coefficient and wind coefficient under various parameters were quantitatively analyzed and summarized. The results shows that the shape coefficients of outer surfaces reach maximum at orthogonal wind direction, and the shape coefficients of all inner surfaces are negative, the maximum absolute value of the shape coefficient is significantly greater than that of conventional high-rise buildings. The thickness ratio and L-angle of the double L-shaped section have a slight influence on the wind force coefficient, while the aspect ratio has a significant influence. The cross-wind and torsional wind force coefficients of double L-shaped high-rise buildings are much greater than those of conventional high-rise buildings at specific aspect ratios. The relevant results can provide reference for the wind-resistant design of similar high-rise buildings.
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CHEN Yuying, HE Lingkong, LI Liu, LI Yanjie*, HE Jin
2025,40(2):183-192 ,DOI: 10.7520/1001-4888-24-056
Abstract:
To investigate the reduction effect of air-jetting on the penetration resistance of objects moving in sandy soil, experimental studies were conducted to examine the influences of key factors such as airflow velocity, number and distribution of airflow outlets, and soil moisture content on horizontal penetration resistance, using the penetration test platform with adjustable functions of penetration speed and airflow velocity. The results with air-jetting were compared with the penetration resistance without air-jetting. During jetting penetration in dry sand, only sand particles at and above the jet outlet’s position are dispersed by the airflow, while the lower particles are almost undisturbed. Under the influence of airflow, local fluidization of dry sand particles occurs, leading to a significant reduction in penetration resistance, with a more obvious effect at higher airflow velocity. For wet sand, air-jetting can also reduce the penetration resistance. Without air-jetting, the penetration resistance in dry sand linearly increases as moisture content is in the range of 0 to 20%, while the increase of moisture content leads to an exponential growth in penetration resistance with air-jetting. In the experiments, the maximum drag reduction percentage for dry sand is 63.5%, and it is 35.5% for wet sand penetration with 20% moisture content. We kept the total air pressure as a constant and changed the number and distribution of jet outlets. The drag reduction percentage for dry sand is around 20%, while it is within 10% for wet sand. Optimal drag reduction is achieved with a single outlet jetting at the front of the intruder.
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CHEN Lianxi, HU Chenchen, QIAN Wen, LAI Junnan, WANG Xiaojian*, ZHAO Chunwang*
2025,40(2):193-207 ,DOI: 10.7520/1001-4888-25-007
Abstract:
Magnesium (Mg) and its alloys, due to their excellent mechanical properties and in vivo degradability, have attracted widespread attention from biomedical device researchers. However, the rapid degradation rate of Mg alloys in physiological environment limits their application. As a load-bearing implant, Mg device is prone to stress corrosion cracking (SCC) under the combined effect of physiological load and corrosive media, leading to premature material fracture failure. Therefore, this paper intends to prepare various surface modification coatings, such as ceramic micro-arc oxidation (MAO) film, poly(lactic-co-glycolic acid) (PLGA) polymer coating with good biocompatibility and degradability, and MgF2 conversion layer, to improve the corrosion resistance and SCC behavior of biomedical Mg alloys. The microstructure, corrosion resistance, and phase composition of the AZ31 and ZK40 substrates, as well as the surface modified layers, were measured by scanning electron microscopy (SEM), optical microscopy (OM), and X-ray diffraction (XRD). The corrosion behavior of uncoated and surface modified Mg substrates were analyzed by potentiodynamic polarization (PDP). Slow strain rate tensile (SSRT) testing was performed in Hank’s solution to obtain the engineer stress-strain curves, and the fracture morphology characteristics of different samples were analyzed. The results indicate that although the same modified layers on the surface of AZ31 and ZK40 substrates exhibit similar corrosion rate, there are significant differences in the resistance to SCC. PLGA coating shows the best corrosion resistance, while lowest resistance to SCC in all surface coated samples. Compared the data of SCC susceptible indices, the MAO film is the best inhibitor of SCC for AZ31 alloy, while the MgF2 conversion layer is preferable for ZK40 alloy.
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HU Jicen, XU Jingchao, ZHANG Ruyue, LAI Lizhao, MIAO Hong*
2025,40(2):208-220 ,DOI: 10.7520/1001-4888-24-063
Abstract:
In using subset-based digital image correlation (DIC) to detect non-uniform deformation, systematic errors caused by undermatched shape functions have always been the primary source of error compared with other factors like noise and grey-level interpolation. The current Quasi-Gauss Point Method is based on one-dimensional displacement assumption, whereas the heterogeneous complex deformation field in the real case is generally two-dimensional. Based on this situation, the Improved Quasi-Gauss Point Method is proposed. Based on the undermatched systematic error function in the subset under two-dimensional displacement, the method deduces the more universal zero-undermatched-systematic-error locations inside subsets, and uses these points as the calculation points of subsets. The results of experiments show that the proposed method has better stability and reliability than the traditional Quasi-Gauss Point Method in the compensation of undermatched systematic errors in two-dimensional complex deformation fields.
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TANG Jupeng*, ZHANG Xiao, LAI Tangrui, YU Honghao
2025,40(2):221-232 ,DOI: 10.7520/1001-4888-24-023
Abstract:
During the injection of carbon dioxide (CO2) in different phases into hard-to-reach coal seams, complex physical and chemical reactions occur, and the variation laws of the seepage characteristics of the coal seam reservoirs caused by this remain significant research gaps. To address these issues, this paper took the mining area of Mindong No.1 Mine in Inner Mongolia as the research object. Coal samples from Mindong No.1 Mine were placed in a self-made triaxial adsorption and permeability instrument. The adsorption experiments of different phases of CO2 on the coal samples were conducted by regulating temperature and pressure to simulate the adsorption process of different phases of CO2 in coal seams with poor storage conditions under complex in-situ stress conditions. Firstly, the relationship of permeability with pore pressure and effective stress was obtained by measuring the permeability and wave velocity of the coal samples after adsorption. Then, based on the fracture isolation effect, the deterioration degree of the coal body caused by CO2 was characterized by the wave velocity attenuation rate. The experimental results show that: 1)The evolution of the permeability of the coal samples is controlled by the coupling effect of the matrix expansion effect caused by the phase difference of adsorbed CO2 and the fracture closure behavior caused by the change of effective stress. 2)As the phase of CO2 adsorbed by the coal samples transitions from gaseous to liquid and then to supercritical, the permeability gradually increases due to the enhanced coupling effect of the matrix and fractures. 3)When the coal body adsorbs CO2, internal fractures expand and connect, resulting in a negative correlation between the acoustic wave propagation velocity of the coal body and the injection pressure of CO2. 4)As the phase changes from gaseous to liquid and then to supercritical, the acoustic wave attenuation rate of the coal body gradually increases, improving the internal seepage channels of the coal body.
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WANG Manman, HE Wen*, SHI Wenfang, ZHU Siyu, SHU Wenqi
2025,40(2):233-244 ,DOI: 10.7520/1001-4888-24-015
Abstract:
To investigate the propagation characteristics of guided waves in Basalt Fiber Reinforced Polymer (BFRP) bolts and assess the anchoring quality of BFRP bolts, this study conducted guided wave testing and analyzed the characteristics of guided waveforms, guided wave velocities, and attenuation in both free BFRP bolts and anchored BFRP bolt structures. The experimental results showed that: 1)When guided waves propagate in free BFRP bolts of different diameters, the wave velocity is higher and the attenuation is lower in the 16 mm bolt compared to the 20 mm bolt. 2)When guided waves propagate in the anchored BFRP bolt structures, the trends of wave velocity and attenuation vary with the curing time: there is a significant decrease during the first 7 days, followed by a stabilization. 3)In the frequency range from 35 to 70 kHz, the attenuation of guided waves in anchored models with anchor debond defects is larger than in models without debond defects, and the farther the defect is from the excitation end, the greater the attenuation. 4)By introducing the concept of attenuation difference ratio, an exponential relationship equation between the attenuation difference ratio and the debond location is obtained, by which the quantitative evaluation of the debond location in the anchoring structure of BFRP bolts can be realized.
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YE Zhongbao, WANG Xueru, ZHAO Wen*, CHEN Xudong, PAN Rui, ZHOU Xingui
2025,40(2):245-255 ,DOI: 10.7520/1001-4888-24-035
Abstract:
In order to study the dynamic mechanical properties of concrete under freeze-thaw cycles, a 75 mm split Hopkinson compression bar (SHPB) device was used to conduct a series of tests on concrete specimens subjected to 0, 5, 10, 15, and 20 freeze-thaw cycles. The crack propagation, fracture morphology, energy dissipation, and characterization of concrete damage degree were analyzed. The experimental results show that under the same number of freeze-thaw cycles, the peak stress and energy absorbed during fragmentation of the material increase with the increase of strain rate; as the strain rate increases, the failure characteristics of the specimen transition from more severe damage on the rear end face compared to the front end face to more severe damage on the front end face compared to the rear end face; under the same strain rate, the more freeze-thaw cycles there are, the lower the compressive strength and greater the degree of damage of the material.
Volume 40,2025 Issue 2
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Mechanical behavior and deformation mechanisms of dual-phase cobalt under the combined influence of temperature and strain rate
MI Changhao, CAI Yang, LI Lingxiao, LU Lei
Abstract:
The compression deformation of dual-phase polycrystalline cobalt are investigated across wide ranges of temperatures (173-473 K) and strain rates (0.001-3000 s^(-1)). The stress-strain data of cobalt are obtained. The microstructure of deformed cobalt after different cases are characterized by electron back-scatter diffraction, multiple types of deformation twinning and HCP-FCC transformation are observed, revealing the individual effects of temperature and strain rate on deformation twinning and phase transition. High temperature suppresses deformation twinning and phase transition. High strain rate promotes deformation twinning, but has no significant effect on phase transformation. A Johnson Cook Cowper Symonds (JC-CS) constitutive model is established based on experimental results. The model predictions show good agreement with the experimental data.
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Deformation and Damage Behavior of 7075 Aluminum Alloy under High Strain Rate Loading
Zhang WuJi, Li LingXiao, Cai Yang, Lu Lei
Abstract:
This paper conducts thin-plate perforation experiments on 7075 aluminum alloy to investigate its deformation and damage mechanisms under different impact loads. First, elemental composition analysis and multi-scale microscopic characterization are performed on the initial samples. A 304 stainless steel spherical projectile is launched from the two-stage gas gun to impact the 7075 aluminum alloy thin plate. The experimental process is recorded by a high-speed camera. Combined with the recovered target plate samples after the experiment, three-dimensional laser scanning and microscopic characterization are carried out on the morphology of the bullet holes and projectiles.Ballistic impact experiments show that the main failure modes of the 7075Al alloy thin plate under the perforation of spherical projectiles are dimples, bulges, and plugging. Meanwhile, phenomena such as projectile wear and debris shedding occur. On the impact side of the target plate, numerous metal melting phenomena are observed, along with brittle fracture. The side walls of the bullet holes exhibit failure modes under the combined action of tension and shear.Based on the Johnson?Cook and Cowper-Symonds constitutive models, finite element simulations are conducted for the high-speed penetration, high-speed perforation processes. By comparing and integrating the simulation results with the experimental data, the distribution of numerical values such as equivalent plastic strain and shear stress at different times during the experimental process in the finite element simulations is analyzed. The simulations well reflect the perforation process of the projectiles.
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Anand Asundi, Vijay Raj Singh*, Pinghua Zhong
2006,21(1):1-10
Abstract:
Digital Holography (DH) has brought a new impetus to the field of holography. The fields of imaging, microscopy and metrology have all benefited from these developments. In this paper some of these developments will be described with some applications in the fields of color imaging, amplitude and phase microscopy and dynamic metrology. It is envisaged that this field will rapidly advance in the next couple of years and become an expected imaging and measurement modality especially in the field of micro, nano and bio sciences.
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WANG Zhenshan, LI Yakun, WEI Jun*, LU Junlong, GUO Hongchao, TIAN Jianbo
2020,35(6):1060-1070 ,DOI: 10.7520/1001-4888-19-189
Abstract:
Basalt fiber concrete has been widely used in the engineering field in our country. In order to study its corrosion resistance and mechanical property degradation in chloride environment, 10 kinds of mix proportion are designed and tested in 5% NaCl solution. The size of the test block is 100mm×100mm×100mm. The apparent cracks, effective porosity, water absorption and mass of the block are measured every 30 days; the axial compressive strength test is conducted every 90 days to determine the change of mechanical properties. It is found that the addition of basalt fiber can effectively inhibit the generation and development of concrete cracks and reduce the migration rate of chloride ions. Compared with the ordinary concrete, adding proper amount of basalt fiber can better improve the compressive strength and deformation ability of concrete. When the volume fraction of fiber is 0.1%, it is the most favorable, while when the parameter is more than 0.2%, the performance is reduced. In addition, it is found that the addition of fly ash is not ideal to reduce the effective porosity of basalt fiber concrete and slow down the migration of chloride ions. It is suggested that the thickness of basalt concrete protective layer should not be less than 30mm in chloride corrosion environment. Finally, on the basis of experiments, the strength degradation model of basalt fiber concrete under chloride erosion is proposed. This study will provide some technical support for the application of basalt fiber concrete in chloride environment.
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HUANG Cheng, GUAN Banglei, SU Zhilong*, ZHANG Dongsheng, YU Qifeng
2021,36(4):429-439 ,DOI: 10.7520/1001-4888-21-039
Abstract:
Non-contact motion tracking based on image and vision is currently an active research field in photomechanics, and it has been widely used in scientific research and engineering measurement. This paper introduces a long-range multi-point 3D real-time motion measuring instrument based on the principle of stereo vision. The system is composed of two independently working stations. Each station has complete high-speed image acquisition, distance measurement, attitude perception, motion control and data processing function. To realize remote measurement, the stations communicate and exchange data through network cables or wireless transmission to form a cooperative measurement mode of “main station + secondary station”. In the three-dimensional calculation, the automatic calibration of the dual-station camera is realized by using scene features, and the stereo matching and temporal tracking are performed based on the efficient digital image correlation principles, realizing the real-time measurement of multi-point three-dimensional motion. The accuracy of the measurement system is verified by the indoor rigid body translation experiment; the feasibility of the measurement device in the long-distance large field of view measurement is proved through the measurement of the actual wind turbine blade movement trajectory.
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FAN Yu-jiang*, YU Bin-shan, LU Yuan-long, WU Qiang-feng, SUN Ke-qing
2020,35(1):159-166 ,DOI: 10.7520/1001-4888-18-146
Abstract:
Three full-featured reinforced interior joints of enhanced recycled aggregate concrete(EC-RAC) frame were considered in the low-cyclic loading test. The evolution process of seismic damage was studied, in which actual damage state and damage index were also determined. Meanwhile, a modified Park-Ang dual-parameter damage model was proposed, since the traditional model could not accurately describe the damage evolution and cumulative behavior of the EC-RAC frame joints after loading displacement greater than 100mm. The coefficients of fiber term, displacement term and energy term were fitted based on the above test results. Finally, taking HF-RAC2 as an example, the error of the damage index was analyzed based on the developed model. The results show that the average error is within 6%, which means the damage model can be applied to the EC-RAC frame joints for seismic damage and evaluation analysis.
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LI He-wan*, WANG Lai-gui, ZHANG Chun-hui, DU Wei, LI Jian-peng
2016,31(1):119-126 ,DOI: 10.7520/1001-4888-15-069
Abstract:
In order to analyze the influence of liquid nitrogen immersion on the fatigue crack extension in water cut coal seam, dry coal samples, 50% water saturated coal samples and 100% water saturated coal samples were collected respectively, and a cyclic fatigue liquid nitrogen immersion experiment was carried out in laboratory. The changes of crack structure on coal sample surface before and after liquid nitrogen immersion was observed by laser microscope and the crack extension velocity was measured by sound wave tester. Results show that 1)liquid nitrogen immersion has no obvious effect on the dry coal samples, which were still intact after 10 immersion cycles; 2)the crack extension is mainly along the vertical direction to joint;3)the higher the water saturated degree is, the more obvious the crack extension of coal sample; 4) the higher the water saturated degree is, the shorter the immersion period required by liquid nitrogen immersion. The water saturation percentage of coal specimen has remarkable effect on the coal crack growth due to liquid nitrogen immersion.
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CHAI Hai-wei, LI Hai-yang, FAN Duan, HUANG Jun-yu*
2020,35(2):225-233 ,DOI: 10.7520/1001-4888-18-263
Abstract:
In order to reveal the relationship between the microstructures and properties of polyurethane foam, an in-situ CT system is built on the 2BM line of APS light source in the US. The deformation and damage of a closed-cell rigid polyurethane foam under quasi-static compression loading is characterized in a three-dimensional (3D), real-time manner, with a resolution of 0.87μm. The stress-strain curve of the rigid polyurethane foam and the evolution of 3D structures in three deformation stages (elastic, platform and densification) are obtained via the in-situ CT test. 3D images show that the local compression bands are observed to propagate from the ends of sample to the center in the platform stage, and the band propagation velocity exceeds the platern velocity. The axial deformation fields of polyurethane foam are calculated accurately using the digital volume image correlation technique, showing that the compression deformation is mainly concentrated in the deformation bands. The deformation process of cells is tracked and the micro deformation of cell walls is quantified with the curvedness index. It is found that the collapse of cells is mainly originated from the folds formed by the buckling of cell walls.
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XU Shan-hua*, ZHANG Hai-jiang, BAI Ye
2019,34(6):1061-1067 ,DOI: 10.7520/1001-4888-18-073
Abstract:
The effects of corrosion on bending performance of channel steel beams were studied through the bending test of 7 corroded channel steel members. The experimental results show that the bearing capacity of corroded channel steel beam has a good linear relationship with the residual flange thickness, and the residual flange thickness can be used to characterize the degree of corrosion. The load-deflection curves and moment-curvature curves can be roughly divided into two stages: elastic stage and elastic-plastic stage. The curves of some specimens have small slopes at the beginning of loading. According to the experimental study, the formula of bearing capacity based on residual flange thickness and corrosion ratio is proposed. The formula has enough reliability.
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ZHANG Yan-bo*, LI Kun, LIU Xiang-xin, TIAN Bao-zhu, YAO Xu-long, LIANG Peng, SUN Lin
2018,33(6):902-910 ,DOI: 10.7520/1001-4888-17-099
Abstract:
In this paper, in order to investigate the effect of the acoustic emission sensor on rock fracture monitoring, biaxial loading experiment of granite with holes was carried out. Selecting two types of sensor: R6α (narrow band) and Nano30 (broad band) to simultaneously monitor rock failure process, the similarities and differences of the time-frequency characteristics received by two types of sensor were analyzed. The applicability of two types of sensors from the working frequency band and sensitivity is discussed in this paper, and then the selection principle of AE sensors in rock fracture monitoring is put forward.Study results show that in time domain, the energy evolution pattern of acoustic emission signals received by two types of sensor is consistent. In frequency domain, the main frequency of R6α sensor received signals is concentrated in 33~110kHz, while the main frequency of Nano30 sensor received signals is uniformly distributed within 0 ~ 500kHz. The signal received by R6α narrow frequency sensor has high intensity and large data amount, which can insulate the interference of noise signal in other frequency bands. So it is suitable for analyzing the timing pattern of rock rupture. Nano30 broad band sensor can guarantee signal integrity in frequency, and can be used to analyze acoustic emission signal waveform and frequency characteristics of rock.
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ZHANG Ye*, SHANG Ke-ming, DU Jian, QI Kai-wen, TIAN Hong-lei, LIN Peng
2020,35(4):659-668 ,DOI: 10.7520/1001-4888-18-249
Abstract:
According to the geometrical characteristics of high-speed train bogie cabins, five design variables are extracted and six schemes are designed. The 1∶8 scaled high-speed train model with subgrade, track and bogie cabin is tested in wind tunnel, and the side slip angles of 0° and -19.8° are used in experiments. The aerodynamic drag characteristics of high-speed train corresponding to different design variables of bogie cabins are analyzed, and the drag reduction effect of each design parameter is obtained. The results show that the aerodynamic drag of the train can be reduced when the top surface of the cabin adopts the curved transition, the front and rear walls adopt inclined walls, the skirt adopts the fully enclosed skirt plate, and the longitudinal length of the inner wall is reduced. The influence of different design variables on the aerodynamic drag is analyzed, which indicates that the inner top chamfer and the longitudinal length of the inner wall have important influences on the aerodynamic drag of the train with side slip angles of 0° and -19.8°. The results have great significance for understanding the local drag reduction and the shape optimization of the train.
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A universal measurement technology for material mechanical properties under aero-thermal environment
WANG Mei-ling*, SUN Dong-bai, ZHAO Fei, YANG Jian-hong, WANG Feng-ping
2019,34(2):275-283 ,DOI: 10.7520/1001-4888-18-118
Abstract:
The “thermal barrier” caused by aerodynamic heating during flight of the aircraft has the characteristics of transient(short-term) high temperature. In this transient high-temperature environment, the strength of the structural material of the aircraft becomes extremely complicated due to temperature and time effects. Conventional steady-state (long-term) high-temperature mechanical properties can no longer reflect the characteristics of the material “thermal barrier” environment. In this paper, a test technique for mechanical properties of materials under aerodynamic thermal environment is proposed and systematically verified with the GH3039 alloy. Actual aero-thermal environment can be simulated, mechanical performance of the structural materials at transient high temperatures can be tested, and the real strength information in the “thermal barrier” service environment can be obtained. This technology provides a new idea and development direction for testing the high temperature mechanical properties of aircraft structural materials.
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MA Yu, LEI Zhen-kun*, FENG Yang, BAI Rui-xiang*
2019,34(4):563-573 ,DOI: 10.7520/1001-4888-18-243
Abstract:
The impregnation of flexible fabric with shear thickening fluid (STF) is a potential method for surface modification of bullet-proof fabrics, which can significantly increase the pullout force and pullout energy of yarns, thereby increasing the impact resistance of flexible fabrics. In this work, the STF-impregnated Kevlar 49 plain fabric with SiO2 as the disperse phase and ethylene glycol (EG) as the dispersant is prepared. The yarn pullout tests are performed on the neat fabric and the STF-impregnated fabric respectively, showing that the load-displacement curves of the neat fabric and the STF-impregnated fabric present similar tendency and can be divided into two stages of static friction and dynamic friction. Unlike the neat fabric, the ultimate pullout load of the STF-impregnated fabric occurs in the dynamic friction stage and is significantly larger than that of the neat fabric. In addition, the pullout energy and the in-plane shear deformation of the STF-impregnated fabric are significantly improved, which are related to the mass fraction of STF and the yarn pullout rates.
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CHEN Bing, SHI Xun-xian, ZHANG Guo-wen, WANG Wen-xiu, YU Qiao-yan, ZHAO Hui-jun, YUAN Xiong-jun, ZHOU Ning
2019,34(2):267-274 ,DOI: 10.7520/1001-4888-18-131
Abstract:
Based on the gas cloud deflagration experimental platform, the propane-air premixed gas blasting experiments inside curved pipelines of different length are carried out. The curved pipeline length effect on the combustible gas explosion in pipeline and the explosion shock wave effect on thin-walled pipeline loading are investigated. Photoelectric, pressure and strain sensors are used to evaluate the explosion parameters within the pipeline and the stress-strain relation of the thin-walled pipeline, respectively. The results indicate that a longer pipeline corresponds to the higher wall overpressure and the bigger maximum strain of the pipeline wall. The pressure-time curve is in good agreement with the thin-walled pipeline strain-time history curve. The curved shape of the pipeline accelerates the flame propagation to a certain extent, and the flame propagation rate decreases to the minimum value at the 90 degree inflexion. The pipeline length has global effects on the flame deflagration within the pipeline. A longer pipeline results in higher pressure and flame speed. The maximum explosion pressure appears at the end of the pipeline, and the loading of the shock wave to the pipeline wall belongs to the dynamic loading.
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ZHANG Hui*, LI Guo-sheng, JIANG Shuai-qi
2018,33(6):979-986 ,DOI: 10.7520/1001-4888-17-107
Abstract:
Aiming at the difficult problem of large deformation and destruction of surrounding rock in super-kilometer deep shaft roadway, the influence of surrounding rock stress and strain evolution and rock dip angle on roadway stability was analyzed by similar simulation experiment. The time-space evolution pattern of deformation and destruction in super-kilometer deep shaft roadway is revealed. Experimental results indicate that due to the existence of rock dip angle, stress concentration appears at the two corners of roadway bottom floor. With the increase of external load, the upper left corner of arch and roadway bottom right corner are destroyed at first, and then extend to deep surrounding rock. Large scale deformation and destruction appear in surrounding rock of roadway. The stress concentration on both left and right sides of roadway intensifies. The displacement quantity of roadway surrounding rock at each position is quite different, the displacement quantity of both arch and roadway floor is larger, the displacement quantity at both sides is relatively small, the maximum deformation quantity is more than 30mm. The deformation and destruction characteristics of surrounding rock in super-kilometer deep shaft roadway can be divided into three stages: slow deformation stage, severe deformation stage and severe deformation and destruction stage. The surrounding rock of roadway produces large deformation and asymmetric destruction, and the destruction range is large. The maximum damage depth of roof and floor is up to 34mm, the surrounding rock of roadway loses its bearing capacity, and roadway space is completely closed. By applying above experimental results to engineering practice, the scheme of full section high strength prestressed bolting net support and strengthening support in special part of super-kilometer deep shaft roadway in Huafeng Coal Mine was put forward, which has achieved an ideal effect.
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HANG Chao*, SU Er-dun, YAN Qun, HUANG Wen-chao
2019,34(1):157-165 ,DOI: 10.7520/1001-4888-17-111
Abstract:
Dynamic characteristic parameters of two kinds of phenyl silicone rubber vibration isolator in aeroengine were studied experimentally. Firstly, the theoretical model of experimental measurement method was established, and the error of engineering approximate formula used in dynamic characteristic parameters calculation of isolator was analyzed. The accurate formulas and iterative algorithm were given. The dynamic stiffness and damping ratio of two isolators were measured by sweep vibration method at room temperature along three axes, and the dynamic stiffness and damping ratios of two isolators along x direction and at different ambient temperatures were also measured by same method. Experimental results show that at room temperature, the dynamic stiffness of two isolators along x direction is much larger than that along y and z direction. With the increase of ambient temperature, the dynamic stiffness of two isolators along x direction decreases gradually. The dynamic stiffness and damping ratio of the improved isolator with damping additive are greater than that of ordinary isolator.
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LI Sa*, LIU Fu-shi, DAI Xu, ZHANG Yan-long
2019,34(1):88-94 ,DOI: 10.7520/1001-4888-17-192
Abstract:
The influence of calcium carbonate content on particle breakage and macroscopic mechanical properties of calcareous sand was systematically studied by indoor experiment. Experimental results show that the calcium carbonate content of the calcareous sand taken from the South China Sea is 95.8% and the calcareous sand is characterized by the angularity, and high void ratio. The breakage of calcareous sand is essentially result from stress concentration between particles; with the increase of calcium carbonate content and particle size, the friction angles and relative breakage index of calcareous sand increase significantly. Particle breakage not only leads to the particle size distribution into good gradation, but also caused the shear strength envelope expressed nonlinear characteristic under higher normal stress; and with the change of the normal stress and the calcium carbonate content, a set of two variables hyperbola function can be used to describe the change rule of relative breakage index.
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SHAN Jun-fang, XU Song-lin*, ZHANG Lei, CHEN Li-na, WANG Peng-fei
2020,35(1):41-57 ,DOI: 10.7520/1001-4888-19-121
Abstract:
Dynamic friction slip of rock joint is prevalent in seismic wave propagation and plate sliding. At present, great attention has been paid to revealing the sliding friction characteristics under large displacement, but the related characteristics at initial stage of friction-slip are seldom studied. The measurement techniques including the multi-point acoustic emission method and the infrared temperature method are established based on the modified split Hopkinson pressure device (SHPB), and the characteristics of acoustic emission and heat production at initial stage of friction sliding on the joint surfaces with five joint angles are investigated. The results show that wave profiles corresponding to the wave-induced micro slip is located at the higher frequency domain of the acoustic emission signals, e.g., frequencies ranging from 78.1kHz to 312.5kHz for granite specimens with size 50×50×50mm3. While the signal measured at the lower frequency domain originates from the disturbances impacting the interface. Wave profiles corresponding to the heat radiation information is located at the lower frequency domain in the temperature signals, and the measured amplitudes of elevated temperature of five joint surfaces are obviously lower. To reveal the intrinsic rules of these measured signals, a reasonable analysis model based on the numerical method is established. The numerical results show that with increasing the joint angle, the joint surface slides more easily, and the amplitude of elevated temperature on the joint surface increases, which is always lower than 0.1℃. The calculations are in good agreement with the experimental results.
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KANG Pu, JIN Jia-xu*, LIANG Bing, ZHANG Ping-yi, SUN Yang
2019,34(3):526-536 ,DOI: 10.7520/1001-4888-18-189
Abstract:
Hydraulic erosion indoor experiments are conducted by considering the soil erosion of the iron tailings pond and the restoration of the ecological environment of the reservoir area. The time-varying law of runoff modulus, the time-varying law of erosion modulus, the rate of total infiltration and vegetation interception and full interception of vegetation of the tailings pond slope are studied under the four working conditions of tall fescue, star grass, bison grass and bare slope. Based on the indoor direct shear test of root-tailing sand complex, the variation of cohesion and internal friction angle of buffalo root-tailing sand complex under different root contents and growth times are studied. Furthermore, the effects of root content and growth time of the buffalo grass on the erosion resistance of iron tailings sand are analyzed. The optimum root content and root growth time of the root-tailing sand shear strength and slope erosion resistance are determined. The results show that the buffalo grass is the preferred grass species in the soilless vegetation slope protection project of iron tailings reservoir. The buffalo grass root serving as the reinforcement material of iron tailings sand can dramatically improve the cohesive force of tailings sand and the slope erosion resistance. The cohesive force of root-tailing sand gradually increases and then decreases with the increase of root growth time and root content, which is always higher than that without buffalo grass. The optimal growth time of the buffalo grass is three months, and the optimal root amount is about 0.20%, which has little effect on the internal friction angle of iron tailings reservoir.
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QIAO Mei-xia, PAN Zhi-wei, HUANG Sheng-hong*, SU Yong, ZHANG Qing-chuan
2020,35(4):557-566 ,DOI: 10.7520/1001-4888-19-066
Abstract:
The mechanical behavior of tungsten under high temperature conditions has great significance and important reference value in fusion reactor engineering as tungsten is currently the first choice of plasma facing materials of the divertor and the first walls.. In this paper, the thermal expansion deformation of tungsten material in temperature range of 25℃ and 2000℃ is measured by a digital image correlation (DIC) equipment based on a vacuum high-heat-flux comprehensive experimental platform, in which a special speckle preparation technique using tantalum carbide powder is developed and two kinds of DIC light path arrangements with external and self-radiation blue light source respectively are designed and realized. The measurement results are in good agreement with those calculated by an empirical correlation equation provided from material handbook (the general error is less than 1%), validating the feasibility and accuracy of adopted measuring techniques. The techniques developed in present investigation lay good foundation for further development of measurement technology of materials under high heat flux shock in fusion engineering.
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GUO Bao-qiao*, CHEN Peng-wan, XIE Hui-min, DAI Fu-long, Fabrice PIERRON
2011,26(5):565-572
Abstract:
Optical full-field measurement is now widely applied in modern experimental mechanics. Mechanical constitutive parameters measurement, such as Young's modulus and Poisson's ratio are first focused on displacement values based on typical loading experiment including tension test or bending test combined with optical measurement (Moire technique and digital image correlation technique) , then the parameters can be identified by calculation by using the load and the strain informations. In this paper, a so-called virtual displacement field method for graphite material constitutive parameters identification is presented. Non-uniform deformation field on specimen surface were measured by the digital image correlation technique, based on three-point bending test of graphite material specimen. By selecting two groups of different virtual displacement field, elastic parameters (Young's Moduls and Poisson's ratio) can be inversed. Results show that the elastic parameters of graphite can be successfully identified by this method. Virtual displacement field method has a good potential in further application of material mechanical behavior inspection.
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SUN Ke-ming*, JI Hong-jie, ZHANG Shu-cui
2020,35(2):343-348 ,DOI: 10.7520/1001-4888-18-153
Abstract:
In order to study the influences of shale natural bedding inclination angle and strength on hydraulic fracturing crack growth, indoor hydraulic fracturing experiment was performed. Real-time monitoring of crack growth and water injection pressure information and sample cutting after fracturing were conducted through monitoring holes to analyze the influence of bedding inclination angle and strength on fracturing crack growth. The results indicate that in the hydraulic fracturing process, when the main crack with stable expansion of minimum vertical ground stress is encountered with the bedding plane, the smaller the angle between the bedding plane and the initial fracture expansion direction is, the more easily the main crack will be expanded along the direction of the bedding plane. The greater the angle between the bedding plane and the initial fracture expansion direction is, the more easily the main crack will be expended through the bedding plane in the original direction. When the bedding azimuth, the ground stress and the tensile strength do not change, and the tensile strength of bedding plane is far weaker than the tensile strength of the matrix, the main crack encountering the bedding plane is much easier to extend in the direction of the bedding plane. The closer the tensile strength of bedding plane approaches to that of the matrix, the more easily the main crack will be extended through the bedding plane along the original direction. When the bedding azimuth and strength do not change, the main crack is much easier to expend through the bedding plane along the original direction for the greater ground stress and stress difference.
