Inspired by the thermal stability mechanism of thermophilic protein,which presents ionic bonds that have better stability at higher temperatures,this paper proposes the introduction of electrostatic interactions by ad...Inspired by the thermal stability mechanism of thermophilic protein,which presents ionic bonds that have better stability at higher temperatures,this paper proposes the introduction of electrostatic interactions by adding carboxyl-modified silica(C-SiO2),PAA,and CaCl_(2) to achieve higher viscosity over 25℃.The rheological behavior of C-SiO_(2)-based shear thickening fluid(CS-STF)was investigated at a temperature range of 25–55℃.Unlike SiO_(2)-based STF,which exhibits single-step thickening and a negative correlation between viscosity and temperature.As the C-SiO_(2) content was 41%(w/w)and the mass ratio of PAA:CaCl_(2):C-SiO_(2) was 3:1:10,the CS-STF displayed a double-thickening behavior,and the peak viscosity reached 1330 Pa·s at 35℃.From the yarn pull-out test,the inter-yarn force was significantly increased with the increasing CS-STF content.Treating UHMWPE fabrics with CS-STF improved the impact resistance effectively.In the blunt impact test,the U-CS fabrics with high CS-STF content(121.45 wt%)experienced penetration failure under high impact energy(18 J)due to stress concentration caused by the shear thickening behavior.The knife stabbing test demonstrated that U-CS fabrics with appropriate content(88.38 wt%)have the best stabbing resistance in various impact energies.Overall,this study proposed a high-performence STF showing double-thickening and enhancing shear-thickening behavior at a wide temperature range,the composite fabrics with the performance of resisting both the blunt and stab impact had broad application prospects in the field of personal protection.展开更多
The advancement of rail transportation necessitates energy absorption structures that not only ensure safety but also optimize space utilization,a critical yet often overlooked aspect in existing designs.This study pr...The advancement of rail transportation necessitates energy absorption structures that not only ensure safety but also optimize space utilization,a critical yet often overlooked aspect in existing designs.This study presents a compact energy absorption structure(CE)that integrates the advantages of cutting rings and thin-walled tube modules,offering a solution with the high space utilization and the superior crashworthiness.Through theoretical modeling and experimental validation using a drop-weight test system,we analyzed the dynamic response and energy absorption characteristics of the CE.Comparative analysis with existing structures,namely the cutting shear rings(CSR)energy absorption structure and thin-walled tube structure(TW),revealed that the CE significantly improves specific energy absorption(SEA)by 102.76%and 61.54%,respectively,and optimizes crush force efficiency(CFE)by increasing 8.23%and 5.49%compared to CSR and TW.The innovative design of the CE,featuring deformation gradient and delay response strategies,showcases its potential for practical application in engineering,advancing the field of crashworthiness engineering.展开更多
In order to study the influence of the bolt joint mode on low-velocity projectiles penetrating the composite protective structure,two bolt joint models which connect the composite target to the fixed frame were design...In order to study the influence of the bolt joint mode on low-velocity projectiles penetrating the composite protective structure,two bolt joint models which connect the composite target to the fixed frame were designed,the ballistic test of the bolted composite protective structure with limited span was carried out,and the bearing and failure characteristics of the bolted region,as well as the energy dissipation of each part of the structure,were analyzed.The results show that in the condition of lowvelocity impact,there are three failure modes for the bolted composite protective structure subjected to projectile penetration,including failure of the impact point of the composite target,failure of protective structure connecting components and failure of the holes in the bolted region of the composite target;the failure mode of bolt holes in the bolted region has a great influence on the protection performance,and the allowable value of the bearing capacity of the bolted region depends on the sum of the minimum failure load in the failure modes and the friction force;shear-out failure occurring in the bolt holes in the bolted region exerts the greatest effect on ballistic performance,which should be avoided;When simultaneous failure occurs in the bolted region and the free deformation region of the composite protective structure,the energy absorption per unit surface density of the composite protective structure reaches the maximum,which can give full play to its anti-penetration efficiency.展开更多
Failure of rock under impact loadings involves complex micro-fracturing and progressive damage. Strength increase and splitting failure have been observed during dynamic tests of rock materials. However, the failure m...Failure of rock under impact loadings involves complex micro-fracturing and progressive damage. Strength increase and splitting failure have been observed during dynamic tests of rock materials. However, the failure mechanism still remains unclear. In this work, based on laboratory tests, numerical simulations with the particle flow code(PFC) were carried out to reproduce the micro-fracturing process of granite specimens. Shear and tensile cracks were both recorded to investigate the failure mode of rocks under different loading conditions. At the same time, a dynamic damage model based on the Weibull distribution was established to predict the deformation and degradation behavior of specimens. It is found that micro-cracks play important roles in controlling the dynamic deformation and failure process of rock under impact loadings. The sharp increase in the number of cracks may be the reason for the strength increase of rock under high strain rates. Tensile cracks tend to be the key reason for splitting failure of specimens. Numerical simulation of crack propagation by PFC can give vivid description of the failure process. However, it is not enough for evaluation of material degradation. The dynamic damage model is able to predict the stress-strain relationship of specimens reasonably well, and can be used to explain the degradation of specimens under impact loadings at macro-scale. Crack and damage can describe material degradation at different scales and can be used together to reveal the failure mechanism of rocks.展开更多
The high variability of shock in terrorist attacks poses a threat to people's lives and properties,necessitating the development of more effective protective structures.This study focuses on the angle gradient and...The high variability of shock in terrorist attacks poses a threat to people's lives and properties,necessitating the development of more effective protective structures.This study focuses on the angle gradient and proposes four different configurations of concave hexagonal honeycomb structures.The structures'macroscopic deformation behavior,stress-strain relationship,and energy dissipation characteristics are evaluated through quasi-static compression and Hopkinson pressure bar impact experiments.The study reveals that,under varying strain rates,the structures deform starting from the weak layer and exhibit significant interlayer separation.Additionally,interlayer shear slip becomes more pronounced with increasing strain rate.In terms of quasi-static compression,symmetric gradient structures demonstrate superior energy absorption,particularly the symmetric negative gradient structure(SNG-SMS)with a specific energy absorption of 13.77 J/cm~3.For dynamic impact,unidirectional gradient structures exhibit exceptional energy absorption,particularly the unidirectional positive gradient honeycomb structure(UPG-SML)with outstanding mechanical properties.The angle gradient design plays a crucial role in determining the structure's stability and deformation mode during impact.Fewer interlayer separations result in a more pronounced negative Poisson's ratio effect and enhance the structure's energy absorption capacity.These findings provide a foundation for the rational design and selection of seismic protection structures in different strain rate impact environments.展开更多
The present work is aimed at studying the mechanic properties of the extra-wide concrete self-anchored suspension bridge under static and dynamic vehicle loads. Based on the field test using 12 heavy trucks and finite...The present work is aimed at studying the mechanic properties of the extra-wide concrete self-anchored suspension bridge under static and dynamic vehicle loads. Based on the field test using 12 heavy trucks and finite element simulations, the static deformations of different components, stress increments and distributions of the girder, as well as the vibration characteristics and damping ratio of the Hunan Road Bridge were analyzed, which is the widest self-anchored suspension bridge in China at present. The dynamic responses were calculated using the Newmark-β integration method assisted by the simulation models of bridge and vehicles, the influences on the dynamic impact coefficient(DIC) brought by the vehicle parameters, girder width, eccentricity travel and deck flatness were also researched. The spatial effect of the girder is obvious due to the extra width, which performs as the stress increments distribute unevenly along the transverse direction, and the girder deflections and stress increments of the upper plate change as a "V" and "M" shape respectively under the symmetrical vehicle loads affected by the shear lag effect, cross slope and local effect of the wheels, the maximum of stress increments are located in the junctions with the inner webs. The obvious girder torsional deformation and the apparent unevenness of the hanger forces between the two cable planes under the eccentric vehicle loads, together with the mode shapes such as the girder transverse bending and torsion which appear relatively earlier, all reflect the weakened torsional rigidity of the extra-wide girder. The transverse displacements of towers are more obvious than the longitudinal ones. As for the influences on the DIC, the static effect of the heavier vehicles plays a major role when pass through with a higher speed and the changes of vehicle suspension stiffness generate greater impacts than the suspension damp. The values of DIC in the vehicle-running side during the eccentric travel, affected by the restricts from the static effects of the eccentric moving trucks, are significantly smaller than the vehicle-free side, the increase in the road roughness is the most sensitive one among the above influential factors. The results could provide references for the design, static and dynamic response analysis of the similar extra-wide suspension bridges.展开更多
To explore the influence of double liquid quenching on the cutting performance of the 7A09 aluminum alloy,quasi-static compression and dynamic impact tests were carried out on the 7A09 aluminum alloy after double liqu...To explore the influence of double liquid quenching on the cutting performance of the 7A09 aluminum alloy,quasi-static compression and dynamic impact tests were carried out on the 7A09 aluminum alloy after double liquid quenching using an MTS810.23 universal testing machine and split-Hopkinson pressure bar(SHPB).The experimental data were fitted to obtain the Johnson–Cook constitutive model parameters of the alloy.Simulations of the machining process were carried out using the Deform-3D finite element software.The results showed that the rheological stress increased with the increase in strain rate and the decrease in temperature.The increase in the cutting speed and feed caused the cutting temperature to rise sharply,whereas the influence of the cutting amount on the cutting temperature was weak.Because of the presence of chip nodules,there was extremum in the cutting force vs cutting speed curves.The increase in the feed and cutting depth increased the cutting area Ac,so the cutting force also increased.The simulation results were verified by experiments.The simulation predictions were in good agreement with the test values,and the cutting force and temperature variations with the cutting parameters were the same.Thus,the correctness of the 7A09 aluminum alloy finite element model was verified.展开更多
基金the Major Science and Technology Demonstration Projects in Jiangsu Province(Grant No.BE2022608).
文摘Inspired by the thermal stability mechanism of thermophilic protein,which presents ionic bonds that have better stability at higher temperatures,this paper proposes the introduction of electrostatic interactions by adding carboxyl-modified silica(C-SiO2),PAA,and CaCl_(2) to achieve higher viscosity over 25℃.The rheological behavior of C-SiO_(2)-based shear thickening fluid(CS-STF)was investigated at a temperature range of 25–55℃.Unlike SiO_(2)-based STF,which exhibits single-step thickening and a negative correlation between viscosity and temperature.As the C-SiO_(2) content was 41%(w/w)and the mass ratio of PAA:CaCl_(2):C-SiO_(2) was 3:1:10,the CS-STF displayed a double-thickening behavior,and the peak viscosity reached 1330 Pa·s at 35℃.From the yarn pull-out test,the inter-yarn force was significantly increased with the increasing CS-STF content.Treating UHMWPE fabrics with CS-STF improved the impact resistance effectively.In the blunt impact test,the U-CS fabrics with high CS-STF content(121.45 wt%)experienced penetration failure under high impact energy(18 J)due to stress concentration caused by the shear thickening behavior.The knife stabbing test demonstrated that U-CS fabrics with appropriate content(88.38 wt%)have the best stabbing resistance in various impact energies.Overall,this study proposed a high-performence STF showing double-thickening and enhancing shear-thickening behavior at a wide temperature range,the composite fabrics with the performance of resisting both the blunt and stab impact had broad application prospects in the field of personal protection.
基金Project(12272414)supported by the National Natural Science Foundation of ChinaProject(2023RC3045)supported by the Science and Technology Innovation Plan of Hunan Province,China。
文摘The advancement of rail transportation necessitates energy absorption structures that not only ensure safety but also optimize space utilization,a critical yet often overlooked aspect in existing designs.This study presents a compact energy absorption structure(CE)that integrates the advantages of cutting rings and thin-walled tube modules,offering a solution with the high space utilization and the superior crashworthiness.Through theoretical modeling and experimental validation using a drop-weight test system,we analyzed the dynamic response and energy absorption characteristics of the CE.Comparative analysis with existing structures,namely the cutting shear rings(CSR)energy absorption structure and thin-walled tube structure(TW),revealed that the CE significantly improves specific energy absorption(SEA)by 102.76%and 61.54%,respectively,and optimizes crush force efficiency(CFE)by increasing 8.23%and 5.49%compared to CSR and TW.The innovative design of the CE,featuring deformation gradient and delay response strategies,showcases its potential for practical application in engineering,advancing the field of crashworthiness engineering.
基金the financial support of the National Natural Science Foundation of China(Grant nos.51679246)。
文摘In order to study the influence of the bolt joint mode on low-velocity projectiles penetrating the composite protective structure,two bolt joint models which connect the composite target to the fixed frame were designed,the ballistic test of the bolted composite protective structure with limited span was carried out,and the bearing and failure characteristics of the bolted region,as well as the energy dissipation of each part of the structure,were analyzed.The results show that in the condition of lowvelocity impact,there are three failure modes for the bolted composite protective structure subjected to projectile penetration,including failure of the impact point of the composite target,failure of protective structure connecting components and failure of the holes in the bolted region of the composite target;the failure mode of bolt holes in the bolted region has a great influence on the protection performance,and the allowable value of the bearing capacity of the bolted region depends on the sum of the minimum failure load in the failure modes and the friction force;shear-out failure occurring in the bolt holes in the bolted region exerts the greatest effect on ballistic performance,which should be avoided;When simultaneous failure occurs in the bolted region and the free deformation region of the composite protective structure,the energy absorption per unit surface density of the composite protective structure reaches the maximum,which can give full play to its anti-penetration efficiency.
基金Projects(51274254,51322403)supported by the National Natural Science Foundation of ChinaProject(NCET-11-0528)supported by theProgram for New Century Excellent Talents in University,ChinaProject(2013SK2011)supported by Hunan Province Science andTechnology Plan,China
文摘Failure of rock under impact loadings involves complex micro-fracturing and progressive damage. Strength increase and splitting failure have been observed during dynamic tests of rock materials. However, the failure mechanism still remains unclear. In this work, based on laboratory tests, numerical simulations with the particle flow code(PFC) were carried out to reproduce the micro-fracturing process of granite specimens. Shear and tensile cracks were both recorded to investigate the failure mode of rocks under different loading conditions. At the same time, a dynamic damage model based on the Weibull distribution was established to predict the deformation and degradation behavior of specimens. It is found that micro-cracks play important roles in controlling the dynamic deformation and failure process of rock under impact loadings. The sharp increase in the number of cracks may be the reason for the strength increase of rock under high strain rates. Tensile cracks tend to be the key reason for splitting failure of specimens. Numerical simulation of crack propagation by PFC can give vivid description of the failure process. However, it is not enough for evaluation of material degradation. The dynamic damage model is able to predict the stress-strain relationship of specimens reasonably well, and can be used to explain the degradation of specimens under impact loadings at macro-scale. Crack and damage can describe material degradation at different scales and can be used together to reveal the failure mechanism of rocks.
基金financially supported by National Natural Science Foundation of China,China (Grant No.52022012)National Key R&D Program for Young Scientists of China,China (Grant No.2022YFC3080900)。
文摘The high variability of shock in terrorist attacks poses a threat to people's lives and properties,necessitating the development of more effective protective structures.This study focuses on the angle gradient and proposes four different configurations of concave hexagonal honeycomb structures.The structures'macroscopic deformation behavior,stress-strain relationship,and energy dissipation characteristics are evaluated through quasi-static compression and Hopkinson pressure bar impact experiments.The study reveals that,under varying strain rates,the structures deform starting from the weak layer and exhibit significant interlayer separation.Additionally,interlayer shear slip becomes more pronounced with increasing strain rate.In terms of quasi-static compression,symmetric gradient structures demonstrate superior energy absorption,particularly the symmetric negative gradient structure(SNG-SMS)with a specific energy absorption of 13.77 J/cm~3.For dynamic impact,unidirectional gradient structures exhibit exceptional energy absorption,particularly the unidirectional positive gradient honeycomb structure(UPG-SML)with outstanding mechanical properties.The angle gradient design plays a crucial role in determining the structure's stability and deformation mode during impact.Fewer interlayer separations result in a more pronounced negative Poisson's ratio effect and enhance the structure's energy absorption capacity.These findings provide a foundation for the rational design and selection of seismic protection structures in different strain rate impact environments.
基金Project(51278104)supported by the National Natural Science Foundation of ChinaProject(2011Y03)supported by Jiangsu Province Transportation Scientific Research Programs,China+1 种基金Project(20133204120015)supported by the Research Fund for the Doctoral Program of Higher Education of ChinaProject(12KJB560003)supported by Jiangsu Province Universities Natural Science Foundation,China
文摘The present work is aimed at studying the mechanic properties of the extra-wide concrete self-anchored suspension bridge under static and dynamic vehicle loads. Based on the field test using 12 heavy trucks and finite element simulations, the static deformations of different components, stress increments and distributions of the girder, as well as the vibration characteristics and damping ratio of the Hunan Road Bridge were analyzed, which is the widest self-anchored suspension bridge in China at present. The dynamic responses were calculated using the Newmark-β integration method assisted by the simulation models of bridge and vehicles, the influences on the dynamic impact coefficient(DIC) brought by the vehicle parameters, girder width, eccentricity travel and deck flatness were also researched. The spatial effect of the girder is obvious due to the extra width, which performs as the stress increments distribute unevenly along the transverse direction, and the girder deflections and stress increments of the upper plate change as a "V" and "M" shape respectively under the symmetrical vehicle loads affected by the shear lag effect, cross slope and local effect of the wheels, the maximum of stress increments are located in the junctions with the inner webs. The obvious girder torsional deformation and the apparent unevenness of the hanger forces between the two cable planes under the eccentric vehicle loads, together with the mode shapes such as the girder transverse bending and torsion which appear relatively earlier, all reflect the weakened torsional rigidity of the extra-wide girder. The transverse displacements of towers are more obvious than the longitudinal ones. As for the influences on the DIC, the static effect of the heavier vehicles plays a major role when pass through with a higher speed and the changes of vehicle suspension stiffness generate greater impacts than the suspension damp. The values of DIC in the vehicle-running side during the eccentric travel, affected by the restricts from the static effects of the eccentric moving trucks, are significantly smaller than the vehicle-free side, the increase in the road roughness is the most sensitive one among the above influential factors. The results could provide references for the design, static and dynamic response analysis of the similar extra-wide suspension bridges.
基金Projects(51575289,51705270)supported by the National Natural Science Foundation of ChinaProject(2019GHY112068)supported by the Key Research and Development of Shandong,China
文摘To explore the influence of double liquid quenching on the cutting performance of the 7A09 aluminum alloy,quasi-static compression and dynamic impact tests were carried out on the 7A09 aluminum alloy after double liquid quenching using an MTS810.23 universal testing machine and split-Hopkinson pressure bar(SHPB).The experimental data were fitted to obtain the Johnson–Cook constitutive model parameters of the alloy.Simulations of the machining process were carried out using the Deform-3D finite element software.The results showed that the rheological stress increased with the increase in strain rate and the decrease in temperature.The increase in the cutting speed and feed caused the cutting temperature to rise sharply,whereas the influence of the cutting amount on the cutting temperature was weak.Because of the presence of chip nodules,there was extremum in the cutting force vs cutting speed curves.The increase in the feed and cutting depth increased the cutting area Ac,so the cutting force also increased.The simulation results were verified by experiments.The simulation predictions were in good agreement with the test values,and the cutting force and temperature variations with the cutting parameters were the same.Thus,the correctness of the 7A09 aluminum alloy finite element model was verified.
