This paper relates to the fabrication of aluminium matrix composites with various amounts of Al 2O 3 fiber and SiC whiskers by rheocasting, powder metallurgy process and liquid metal infiltration process. To analy...This paper relates to the fabrication of aluminium matrix composites with various amounts of Al 2O 3 fiber and SiC whiskers by rheocasting, powder metallurgy process and liquid metal infiltration process. To analyze wetting characteristics, the cross sections of composites are examined by scanning electron microscopy(SEM). The bending tests and microhardness tests are performed to evaluate mechanical properties of composites. The results show that the composites produced by liquid metal infiltration give better properties than those produced by rheocasting or powder metallurgy process, primarily due to the decrease of porosity and reinforcement cluster. For liquid metal infiltration composites, a good adhesion between the fiber and matrix is found. Three points bending test results show that there is an increase in flexural modulus with reinforcement contents. In addition, a series of microhardness tests are conducted to determine the effect of heat treatment on the mechanical property of Al 2O 3/Al composites.展开更多
In the recent past,the potential benefits of wraparound geosynthetic reinforcement technique for constructing the reinforced soil foundations have been reported.This paper presents the experimental study on the behavi...In the recent past,the potential benefits of wraparound geosynthetic reinforcement technique for constructing the reinforced soil foundations have been reported.This paper presents the experimental study on the behaviour of model strip footing resting on sandy soil bed reinforced with geosynthetic in wraparound and planar forms under monotonic and repeated loadings.The geosynthetic layers were laid according to the reinforcement ratio to minimise the scale effect.It is found that for the same amount of reinforcement material,the wraparound reinforced model resulted in less settlement in comparison to planar reinforced models.The efficiency of wraparound reinforced model increased with the increase in load amplitude and the rate of total cumulative settlement substantially decreased with the increase in number of load cycles.The wraparound reinforced model has shown about 45% lower average total settlement in comparison to unreinforced model,while the double-layer reinforced model has about 41% lower average total settlement at the cost of approximately twice the material and 1.5 times the occupied land width ratio.Moreover,wraparound models have shown much greater stability in comparison to their counterpart models when subjected to incremental repeated loading.展开更多
Electrochemical techniques of the corrosion measurements of reinforcing steeI in concrete have been evaluated. These techniques include half-cell potential measurements, impressed voltage method, impressed current met...Electrochemical techniques of the corrosion measurements of reinforcing steeI in concrete have been evaluated. These techniques include half-cell potential measurements, impressed voltage method, impressed current method and potentiostatic polarization technique. The results of corrosion behaviour of the steel in both 5%NaCl and 5%MgSO4 show that each electrochemical technique provides some information about the condition of the steel bar or the corrosivity of the environment being evaluated, yet none provides a complete data regarding the corrosion resistance of reinforcing steel in aggressive media展开更多
This paper lists difficult railway construction conditions that are typical for the northern areas of the Russian Far East.Permafrost-bound issues of railway and highway construction and operation are described.Some o...This paper lists difficult railway construction conditions that are typical for the northern areas of the Russian Far East.Permafrost-bound issues of railway and highway construction and operation are described.Some of the authors'developments for subgrade stabilization in the foregoing conditions are given as examples.展开更多
Based on the shear wave tracing(SWT) technique proposed by Tang Z P, particle velocity gauge and the dual internal measurement for pressure and shear waves (IMPS) system are applied to investigate the responses of fib...Based on the shear wave tracing(SWT) technique proposed by Tang Z P, particle velocity gauge and the dual internal measurement for pressure and shear waves (IMPS) system are applied to investigate the responses of fiber reinforced cement subjected to impact loading. Series of experiments are conducted. The results show that there exist four critical points, A, B, C, D, in p-V Hugoniot curves. They correspond to the Hugoniot elastic limit (HEL) of the material, the critical point for shear strength limit and transition from damage state to failure state, void collapse, and solid compression, respectively. The critical point B is difficult to be aware of and never reported. However, it can be clearly disclosed with SWT method. Based on the analyses of shear strength, it can be concluded that the transversal wave, especially the unloading transversal wave, is especially important for the dynamic damage investigation of brittle materials.展开更多
Aluminum matrix composites(AMCs), reinforced with novel pre-synthesized Al/Cu Fe multi-layered coreshell particles, were fabricated by different consolidation techniques to investigate their effect on microstructure a...Aluminum matrix composites(AMCs), reinforced with novel pre-synthesized Al/Cu Fe multi-layered coreshell particles, were fabricated by different consolidation techniques to investigate their effect on microstructure and mechanical properties. To synthesize multi-layered Al/Cu Fe core-shell particles, Cu and Fe layers were deposited on Al powder particles by galvanic replacement and electroless plating method, respectively. The core-shell powder and sintered compacts were characterized by using X-ray diffraction(XRD), scanning electron microscopy(SEM) equipped with energy dispersive spectroscopy(EDX), pycnometer, microhardness and compression tests. The results revealed that a higher extent of interfacial reactions, due to the transformation of the deposited layer into intermetallic phases in spark plasma sintered composite, resulted in high relative density(99.26%), microhardness(165 HV0.3) and strength(572 MPa). Further, the presence of un-transformed Cu in the shell structure of hot-pressed composite resulted in the highest fracture strain(20.4%). The obtained results provide stronger implications for tailoring the microstructure of AMCs through selecting appropriate sintering paths to control mechanical properties.展开更多
Nonlinear solution of reinforced concrete structures, particularly complete load-deflection response, requires tracing of the equilibrium path and proper treatment of the limit and bifurcation points. In this regard, ...Nonlinear solution of reinforced concrete structures, particularly complete load-deflection response, requires tracing of the equilibrium path and proper treatment of the limit and bifurcation points. In this regard, ordinary solution techniques lead to instability near the limit points and also have problems in case of snap-through and snap-back. Thus they fail to predict the complete load-displacement response. The arc-length method serves the purpose well in principle, received wide acceptance in finite element analysis, and has been used extensively. However modifications to the basic idea are vital to meet the particular needs of the analysis. This paper reviews some of the recent developments of the method in the last two decades, with particular emphasis on nonlinear finite element analysis of reinforced concrete structures.展开更多
为了研究20 W纳秒激光对碳纤维复合材料(CFRP)烧蚀的工艺质量,采用单因素实验方法及光切法进行了理论分析和实验验证,得到了扫描速率、峰值功率、离焦量对材料表面加工质量的影响规律,并对0.5 mm CFRP材料板进行了烧蚀实验。结果表明,...为了研究20 W纳秒激光对碳纤维复合材料(CFRP)烧蚀的工艺质量,采用单因素实验方法及光切法进行了理论分析和实验验证,得到了扫描速率、峰值功率、离焦量对材料表面加工质量的影响规律,并对0.5 mm CFRP材料板进行了烧蚀实验。结果表明,调整激光器的离焦量,让激光的焦点与材料平面在同一高度,可使扫描线宽最小,减少了材料烧蚀的热影响区,提高了激光能量利用率;设定激光扫描速率为220 mm/s和峰值功率为10 W,可得到大小为3.50μm的CFRP最小表面粗糙度平均值,其中粗糙度数据稳定性样本方差最佳,约为0.133μm 2,在此条件下可得到良好的加工表现。此研究为脉冲激光加工CFRP材料工艺研究提供一定参考,并为脉冲激光加工复合材料工艺应用打下了一定的实践基础。展开更多
Tungsten inert gas （TIG） welded joints for 2219-T87 aluminum alloy are often used in the fuel tanks of large launch vehicles. Because of the massive loads these vehicles carry, dealing with weld reinforcement on TIG...Tungsten inert gas （TIG） welded joints for 2219-T87 aluminum alloy are often used in the fuel tanks of large launch vehicles. Because of the massive loads these vehicles carry, dealing with weld reinforcement on TIG joints represents an important issue in their manufacturing and strength evaluation. Experimental and numerical simulation methods were used to investigate the effects of weld toe shape and weld toe position on the tensile behavior and mechanical properties of these joints. The simulation results indicated that the relative difference in elongation could be as large as 96.9% caused by the difference in weld toe shape. The joints with weld toes located in the weld metal or in the partially melted zone （PMZ） exhibited larger elongation than joints with weld toes located at the juncture of the weld metal and the PMZ.展开更多
A series of direct shear tests under constant normal loading conditions were carried out on specimens of bolted sandstone single-joint treated with different numbers of dryewet cycles.The experimental results show tha...A series of direct shear tests under constant normal loading conditions were carried out on specimens of bolted sandstone single-joint treated with different numbers of dryewet cycles.The experimental results show that the peak shear strength and shear stiffness of bolted sandstone joints were significantly reduced after 12 dryewet cycles.The decrease in the shear strength of rough joints is more significant than that of flat joints.Due to the decrease in the strength of the surrounding rock,the deformation characteristics of the bolts are significantly affected by the number of dryewet cycles performed.With an increase in the number of dryewet cycles,the plastic hinge length of the bolt gradually increases,resulting in an increase in the corresponding shear displacement when the bolt breaks.Compared with the tensileeshear failure mode of the bolts in flat joints,the tensileebending failure mode arises for bolts in rough joints.A shear curve model describing the whole process of bolted rock joints is established based on the deterioration of rock mechanical parameters caused by dry‒wet cycles.The model proposed considers the change in the friction angle of the joint surface with the shear displacement,which is applied to the derivation of the model by introducing the dynamic evolutionary friction angle parameter.The reasonably good agreement between a predicted curve and the corresponding experimental curve indicates that this method can effectively predict the shear strength of a bolted rock joint involving rough joint under dryewet cycling conditions.展开更多
Underground geotechnical engineering encounters persistent challenges in ensuring the stability and safety of surrounding rock structures, particularly within rocky tunnels. Rock reinforcement techniques, including th...Underground geotechnical engineering encounters persistent challenges in ensuring the stability and safety of surrounding rock structures, particularly within rocky tunnels. Rock reinforcement techniques, including the use of steel mesh, are critical to achieving this goal. However, there exists a knowledge gap regarding the comprehensive understanding of the mechanical behavior and failure mechanisms exhibited by steel mesh under diverse loading conditions. This study thoroughly explored the steel mesh's performance throughout the entire loading-failure process, innovating with detailed analysis and modeling techniques. By integrating advanced numerical modeling with laboratory experiments, the study examines the influence of varying reinforcement levels and geometric parameters on the steel mesh strength and deformation characteristics. Sensitivity analysis, employing gray correlation theory, identifies the key factors affecting the mesh performance, while a BP (Backpropagation) neural network model predicts maximum vertical deformation with high accuracy. The findings underscore the critical role of steel diameter and mesh spacing in optimizing peak load capacity, displacement, and energy absorption, offering practical guidelines for design improvements. The use of a Bayesian Regularization (BR) algorithm further enhances the predictive accuracy compared to traditional methods. This research provides new insights into optimizing steel mesh design for underground applications, offering an innovative approach to enhancing structural safety in geotechnical projects.展开更多
环氧树脂是古建筑木构件修复加固的常用材料,为了科学合理地使用环氧树脂,基于多准则决策理论建立古建筑木构件修复加固用环氧树脂性能评价模型。参考古建筑木构件修复加固工程对环氧树脂的要求与相关标准确定环氧树脂的性能指标集合,...环氧树脂是古建筑木构件修复加固的常用材料,为了科学合理地使用环氧树脂,基于多准则决策理论建立古建筑木构件修复加固用环氧树脂性能评价模型。参考古建筑木构件修复加固工程对环氧树脂的要求与相关标准确定环氧树脂的性能指标集合,采用熵权法与层次分析法分别得到各性能指标客观权重与主观权重,综合主客观权重对各性能指标赋权,使用优序法与逼近理想解排序法(technique for order preference similar to an ideal solution,TOPSIS法)结合各性能指标复合权重构建两种综合性能评价模型。通过验证试验对十组环氧树脂进行综合性能评价,结果表明复合加权TOPSIS综合性能评价模型更全面客观,更适用于古建筑木构件修复加固用环氧树脂,可作为选择和使用环氧树脂的参考方法。展开更多
文摘This paper relates to the fabrication of aluminium matrix composites with various amounts of Al 2O 3 fiber and SiC whiskers by rheocasting, powder metallurgy process and liquid metal infiltration process. To analyze wetting characteristics, the cross sections of composites are examined by scanning electron microscopy(SEM). The bending tests and microhardness tests are performed to evaluate mechanical properties of composites. The results show that the composites produced by liquid metal infiltration give better properties than those produced by rheocasting or powder metallurgy process, primarily due to the decrease of porosity and reinforcement cluster. For liquid metal infiltration composites, a good adhesion between the fiber and matrix is found. Three points bending test results show that there is an increase in flexural modulus with reinforcement contents. In addition, a series of microhardness tests are conducted to determine the effect of heat treatment on the mechanical property of Al 2O 3/Al composites.
基金funded by the Higher Education Commission(HEC),Government of the Islamic Republic of Pakistan and Edith Cowan University,Perth,Australia。
文摘In the recent past,the potential benefits of wraparound geosynthetic reinforcement technique for constructing the reinforced soil foundations have been reported.This paper presents the experimental study on the behaviour of model strip footing resting on sandy soil bed reinforced with geosynthetic in wraparound and planar forms under monotonic and repeated loadings.The geosynthetic layers were laid according to the reinforcement ratio to minimise the scale effect.It is found that for the same amount of reinforcement material,the wraparound reinforced model resulted in less settlement in comparison to planar reinforced models.The efficiency of wraparound reinforced model increased with the increase in load amplitude and the rate of total cumulative settlement substantially decreased with the increase in number of load cycles.The wraparound reinforced model has shown about 45% lower average total settlement in comparison to unreinforced model,while the double-layer reinforced model has about 41% lower average total settlement at the cost of approximately twice the material and 1.5 times the occupied land width ratio.Moreover,wraparound models have shown much greater stability in comparison to their counterpart models when subjected to incremental repeated loading.
文摘Electrochemical techniques of the corrosion measurements of reinforcing steeI in concrete have been evaluated. These techniques include half-cell potential measurements, impressed voltage method, impressed current method and potentiostatic polarization technique. The results of corrosion behaviour of the steel in both 5%NaCl and 5%MgSO4 show that each electrochemical technique provides some information about the condition of the steel bar or the corrosivity of the environment being evaluated, yet none provides a complete data regarding the corrosion resistance of reinforcing steel in aggressive media
文摘This paper lists difficult railway construction conditions that are typical for the northern areas of the Russian Far East.Permafrost-bound issues of railway and highway construction and operation are described.Some of the authors'developments for subgrade stabilization in the foregoing conditions are given as examples.
文摘Based on the shear wave tracing(SWT) technique proposed by Tang Z P, particle velocity gauge and the dual internal measurement for pressure and shear waves (IMPS) system are applied to investigate the responses of fiber reinforced cement subjected to impact loading. Series of experiments are conducted. The results show that there exist four critical points, A, B, C, D, in p-V Hugoniot curves. They correspond to the Hugoniot elastic limit (HEL) of the material, the critical point for shear strength limit and transition from damage state to failure state, void collapse, and solid compression, respectively. The critical point B is difficult to be aware of and never reported. However, it can be clearly disclosed with SWT method. Based on the analyses of shear strength, it can be concluded that the transversal wave, especially the unloading transversal wave, is especially important for the dynamic damage investigation of brittle materials.
文摘Aluminum matrix composites(AMCs), reinforced with novel pre-synthesized Al/Cu Fe multi-layered coreshell particles, were fabricated by different consolidation techniques to investigate their effect on microstructure and mechanical properties. To synthesize multi-layered Al/Cu Fe core-shell particles, Cu and Fe layers were deposited on Al powder particles by galvanic replacement and electroless plating method, respectively. The core-shell powder and sintered compacts were characterized by using X-ray diffraction(XRD), scanning electron microscopy(SEM) equipped with energy dispersive spectroscopy(EDX), pycnometer, microhardness and compression tests. The results revealed that a higher extent of interfacial reactions, due to the transformation of the deposited layer into intermetallic phases in spark plasma sintered composite, resulted in high relative density(99.26%), microhardness(165 HV0.3) and strength(572 MPa). Further, the presence of un-transformed Cu in the shell structure of hot-pressed composite resulted in the highest fracture strain(20.4%). The obtained results provide stronger implications for tailoring the microstructure of AMCs through selecting appropriate sintering paths to control mechanical properties.
文摘Nonlinear solution of reinforced concrete structures, particularly complete load-deflection response, requires tracing of the equilibrium path and proper treatment of the limit and bifurcation points. In this regard, ordinary solution techniques lead to instability near the limit points and also have problems in case of snap-through and snap-back. Thus they fail to predict the complete load-displacement response. The arc-length method serves the purpose well in principle, received wide acceptance in finite element analysis, and has been used extensively. However modifications to the basic idea are vital to meet the particular needs of the analysis. This paper reviews some of the recent developments of the method in the last two decades, with particular emphasis on nonlinear finite element analysis of reinforced concrete structures.
文摘Tungsten inert gas （TIG） welded joints for 2219-T87 aluminum alloy are often used in the fuel tanks of large launch vehicles. Because of the massive loads these vehicles carry, dealing with weld reinforcement on TIG joints represents an important issue in their manufacturing and strength evaluation. Experimental and numerical simulation methods were used to investigate the effects of weld toe shape and weld toe position on the tensile behavior and mechanical properties of these joints. The simulation results indicated that the relative difference in elongation could be as large as 96.9% caused by the difference in weld toe shape. The joints with weld toes located in the weld metal or in the partially melted zone （PMZ） exhibited larger elongation than joints with weld toes located at the juncture of the weld metal and the PMZ.
基金the Natural Science Foundation of China(Grant Nos.42302314 and 52078427)the Open foundation of State Key Laboratory of Geohazard Prevention and Geoenvironment Protection(Grant No.SKLGP2022K001).
文摘A series of direct shear tests under constant normal loading conditions were carried out on specimens of bolted sandstone single-joint treated with different numbers of dryewet cycles.The experimental results show that the peak shear strength and shear stiffness of bolted sandstone joints were significantly reduced after 12 dryewet cycles.The decrease in the shear strength of rough joints is more significant than that of flat joints.Due to the decrease in the strength of the surrounding rock,the deformation characteristics of the bolts are significantly affected by the number of dryewet cycles performed.With an increase in the number of dryewet cycles,the plastic hinge length of the bolt gradually increases,resulting in an increase in the corresponding shear displacement when the bolt breaks.Compared with the tensileeshear failure mode of the bolts in flat joints,the tensileebending failure mode arises for bolts in rough joints.A shear curve model describing the whole process of bolted rock joints is established based on the deterioration of rock mechanical parameters caused by dry‒wet cycles.The model proposed considers the change in the friction angle of the joint surface with the shear displacement,which is applied to the derivation of the model by introducing the dynamic evolutionary friction angle parameter.The reasonably good agreement between a predicted curve and the corresponding experimental curve indicates that this method can effectively predict the shear strength of a bolted rock joint involving rough joint under dryewet cycling conditions.
基金funded by the National Natural Science Foundation of China(Grant No.52178396).
文摘Underground geotechnical engineering encounters persistent challenges in ensuring the stability and safety of surrounding rock structures, particularly within rocky tunnels. Rock reinforcement techniques, including the use of steel mesh, are critical to achieving this goal. However, there exists a knowledge gap regarding the comprehensive understanding of the mechanical behavior and failure mechanisms exhibited by steel mesh under diverse loading conditions. This study thoroughly explored the steel mesh's performance throughout the entire loading-failure process, innovating with detailed analysis and modeling techniques. By integrating advanced numerical modeling with laboratory experiments, the study examines the influence of varying reinforcement levels and geometric parameters on the steel mesh strength and deformation characteristics. Sensitivity analysis, employing gray correlation theory, identifies the key factors affecting the mesh performance, while a BP (Backpropagation) neural network model predicts maximum vertical deformation with high accuracy. The findings underscore the critical role of steel diameter and mesh spacing in optimizing peak load capacity, displacement, and energy absorption, offering practical guidelines for design improvements. The use of a Bayesian Regularization (BR) algorithm further enhances the predictive accuracy compared to traditional methods. This research provides new insights into optimizing steel mesh design for underground applications, offering an innovative approach to enhancing structural safety in geotechnical projects.
文摘环氧树脂是古建筑木构件修复加固的常用材料,为了科学合理地使用环氧树脂,基于多准则决策理论建立古建筑木构件修复加固用环氧树脂性能评价模型。参考古建筑木构件修复加固工程对环氧树脂的要求与相关标准确定环氧树脂的性能指标集合,采用熵权法与层次分析法分别得到各性能指标客观权重与主观权重,综合主客观权重对各性能指标赋权,使用优序法与逼近理想解排序法(technique for order preference similar to an ideal solution,TOPSIS法)结合各性能指标复合权重构建两种综合性能评价模型。通过验证试验对十组环氧树脂进行综合性能评价,结果表明复合加权TOPSIS综合性能评价模型更全面客观,更适用于古建筑木构件修复加固用环氧树脂,可作为选择和使用环氧树脂的参考方法。
