Adopting the classical theory of hydrocodes,the constitutive relations of concretes are separated into an equation of state(EoS)which describes the volumetric behavior of concrete material and a strength model which d...Adopting the classical theory of hydrocodes,the constitutive relations of concretes are separated into an equation of state(EoS)which describes the volumetric behavior of concrete material and a strength model which depicts the shear properties of concrete.The experiments on the EoS of concrete is always challenging due to the technical difficulties and equipment limitations,especially for the specimen size effect on the EoS.Although some researchers investigate the shock properties of concretes by fly-plate impact tests,the specimens used in their tests are usually in one size.In this paper,the fly-plate impact tests on concrete specimens with different sizes are performed to investigate the size effect on the shock properties of concrete materials.The mechanical background of the size effect on the shock properties are revealed,which is related to the lateral rarefaction effect and the deviatoric stress produced in the specimen.According to the tests results,the modified EoS considering the size effect on the shock properties of concrete are proposed,which the bulk modulus of concrete is unpredicted by up to 20% if size effects are not accounted for.展开更多
In order to improve the overall resilience of the urban infrastructures, it is required to conduct blast resistant design for important building structures in the city. For complex terrain in the city, it is recommend...In order to improve the overall resilience of the urban infrastructures, it is required to conduct blast resistant design for important building structures in the city. For complex terrain in the city, it is recommended to determine the blast load on the structures via numerical simulation. Since the mesh size of the numerical model highly depends on the explosion scenario, there is no generally applicable approach for the mesh size selection. An efficient method to determine the mesh size of the numerical model of near-ground detonation based on explosion scenarios is proposed in this study. The effect of mesh size on the propagation of blast wave under different explosive weights was studied, and the correlations between the mesh size effect and the charge weight or the scaled distance was described. Based on the principle of the finite element method and Hopkinson-Cranz scaling law, a mesh size measurement unit related to the explosive weight was proposed as the criterion for determining the mesh size in the numerical simulation. Finally, the applicability of the method proposed in this paper was verified by comparing the results from numerical simulation and the explosion tests and was verified in AUTODYN.展开更多
The macroscopic mechanical properties of rocks are significantly influenced by their microstructure.As a material bonded by mineral grains,the grain morphology of crystalline rock is the primary factor influencing the...The macroscopic mechanical properties of rocks are significantly influenced by their microstructure.As a material bonded by mineral grains,the grain morphology of crystalline rock is the primary factor influencing the strength.However,most strength criteria neglect the strength variations caused by different grain characteristics in rocks.Furthermore,the traditional linear criteria tend to overestimate tensile strength and exhibit apex singularity.To address these shortcomings,a piecewise strength criterion that considers the grain size effect has been proposed.A part of an ellipse was employed to construct the envelope of the tensive-shear region on the meridian plane,to accurately reproduce the low tensile-compressive strength ratio.Based on the analysis of experimental data,both linear and exponential modification functions that account for grain size effects were integrated into the proposed criterion.The corresponding finite element algorithm has been implemented.The accuracy and applicability of the proposed criterion were validated by comparing with the experimental data.展开更多
Deformation characteristics of light weight soil with different EPS (expanded polystyrene) sizes were investigated by consolidation tests.The results show that the confined stress-strain relation curve is in S shape,w...Deformation characteristics of light weight soil with different EPS (expanded polystyrene) sizes were investigated by consolidation tests.The results show that the confined stress-strain relation curve is in S shape,which has a good homologous relation with e-p curve and e-lgp curve,and three types of curves reflect obvious structural characteristics of light weight soil.When cement mixed ratio and EPS volume ratio are the same for different specimens,structural strength decreases with the increase of EPS size,but compressibility indexes basically keep unchanged within the structural strength.The settlement of light weight soil can be divided into instantaneous settlement and primary consolidation settlement.It has no obvious rheology property,and 90% of total consolidation deformation can be finished in 1 min.Settlement-time relation of light weight soil can be predicted by the hyperbolic model.S-lgt curve of light weight soil is not in anti-S shape.It is proved that there is no secondary consolidation section,so consolidation coefficient cannot be obtained by time logarithm method.Structural strength and unit price decrease with the increase of EPS size,but the reducing rate of the structural strength is lower than that of the unit price,so the cost of mixed soil can be reduced by increasing the EPS size.The EPS beads with 3-5 mm in diameter are suggested to be used in the construction process,and the prescription of mixed soil can be optimized.展开更多
In order to investigate the size effect and other effects on the stress-strain relationship of confined concrete, 42 specimens with different sizes and section shapes were placed under axial compression loading. Effec...In order to investigate the size effect and other effects on the stress-strain relationship of confined concrete, 42 specimens with different sizes and section shapes were placed under axial compression loading. Effects of key parameters such as size of specimens, tie configuration, transverse reinforcement ratio, and concrete cover were studied. The results show that for specimens with the same configuration and the same volumetric ratio of the transverse reinforcement, along with the increasing specimen size, the peak stress, peak strain and deformation of the post-peak show a down trend, however, the volumetric ratio of the transverse reinforcement is lowered, the decreasing of the peak stress is accelerated, but the decreasing of the deformation is slow down. For specimens with the same volumetric ratio but different configurations of transverse reinforcement, though the transverse reinforcement configuration becomes more complicated, the peak stress of the large size specimen does not improve more than that of the small size. However, the deformation occurs before the stress declines to 85% of peak stress, and the improvement with the grid pattern tie configuration is much greater due to size effect.展开更多
Uniaxial compression tests on sandstone samples with five different sizes after high temperature processes were performed in order to investigate the size effect and its evolution. The test results show that the densi...Uniaxial compression tests on sandstone samples with five different sizes after high temperature processes were performed in order to investigate the size effect and its evolution. The test results show that the density, longitudinal wave velocity, peak strength, average modulus and secant modulus of sandstone decrease with the increase of temperature, however, peak strain increases gradually. With the increase of ratio of height to diameter, peak strength of sandstone decreases, which has an obvious size effect. A new theoretical model of size effect of sandstone material considering the influence of temperature is put forward, and with the increase of temperature, the size effect is more apparent. The threshold decreases gradually with the increase of temperature, and the deviations of the experimental values and the theoretical values are between 0.44% and 6.06%, which shows quite a credibility of the theoretical model.展开更多
A series of compression tests were conducted on 150 groups of cement paste specimens with side lengths ranging from 40 mm to 200 mm. The specimens include cube specimens and prism specimens with height to width ratio ...A series of compression tests were conducted on 150 groups of cement paste specimens with side lengths ranging from 40 mm to 200 mm. The specimens include cube specimens and prism specimens with height to width ratio of 2. The experiment results show that size effect exists in the cubic compressive strength and prismatic compressive strength of the cement paste, and larger specimens resist less in terms of strength than smaller ones. The cubic compressive strength and the prismatic compressive strength of the specimens with side length of 200 mm are respectively about 91% and 89% of the compressive strength of the specimens with the side length of 40 mm. Water to binder ratio has a significant influence on the size effect of the compressive strengths of the cement paste. With a decrease in the water to binder ratio, the size effect is significantly enhanced. When the water to binder ratio is 0.2, the size effects of the cubic compressive strength and the prismatic compressive strength of the cement paste are 1.6 and 1.4 times stronger than those of a water to binder ratio of 0.6. Furthermore, a series of formulas are proposed to calculate the size effect of the cubic compressive strength and the prismatic compressive strength of cement paste, and the results of the size effect predicted by the formulas are in good agreement with the experiment results.展开更多
In order to gain a deeper understanding of the effect of pulsed current on the mechanical properties and size effect of nanocrystalline Ni foils,nanocrystalline Ni foils with different grain thickness-to-grain size ra...In order to gain a deeper understanding of the effect of pulsed current on the mechanical properties and size effect of nanocrystalline Ni foils,nanocrystalline Ni foils with different grain thickness-to-grain size ratios(λ)were prepared using pulsed electrodeposition in this paper and unidirectional tensile experiments were carried out at room temperature with different currents and their applied directions.The experimental results show that the nanocrystalline Ni foil produces an obvious electroplasticity effect after applying the current field,and when 300<λ<1100,the current weakens the size effect of nanocrystalline Ni foils to a certain extent,and the angle between the current direction and the deformation direction also affects the mechanical response of nanocrystalline Ni foils,and when the angle between the current direction and the deformation direction is 0°,electroplasticity effect is the best,and the current has the most significant effect of abating the size effect of the material.The mechanism of unidirectional tensile deformation of nanocrystalline Ni foils under the effect of pulsed current was analyzed using TEM and TKD.It was found that the applied pulse current increased the activity of the nanocrystalline boundaries,promoted the movement of dislocations,and reduced the tendency of dislocation entanglement.The higher the peak current density and the smaller the angle between the direction of the current and the direction of deformation,the smaller the grain boundary orientation difference,the more dispersed the grain orientation,and the lower the density of geometrically necessary dislocations(GND)in the deformed nanocrystalline foil,the more significant the effect on material plasticity improvement.展开更多
In order to investigate the mechanism of nanoparticles enhancing the heat and mass transfer of the ammonia-water absorption process,several types of binary nanofluids were prepared by mixing Al2O3 nanoparticles with p...In order to investigate the mechanism of nanoparticles enhancing the heat and mass transfer of the ammonia-water absorption process,several types of binary nanofluids were prepared by mixing Al2O3 nanoparticles with polyacrylic acid(PAA),TiO2 with polyethylene glycol(PEG 1000),and TiN,SiC,hydroxyapatite(noodle-like) with PEG 10000 to ammonia-water solution,respectively.The thermal conductivities were measured by using a KD2 Pro thermal properties analyzer.The influences of surfactant and ammonia on the dispersion stabilities of the binary nanofluids were investigated by the light absorbency ratio index methods.The results show that the type,content and size of nanoparticles,the temperature as well as the dispersion stability are the key parameters that affect the thermal conductivity of nanofluids.For the given nanoparticle material and the base fluid,the thermal conductivity ratio of the nanofluid to the ammonia-water liquid increases as the nanoparticle content and the temperature are increased,and the diameter of nanoparticle is decreased.Furthermore,the thermal conductivity ratio increases significantly by improving the stabilities of nanofluids,which is achieved by adding surfactants or performing the proper ammonia content in the fluid.展开更多
The complete splitting process of steel fiber reinforced concrete （SFRC） at intermediate strain rate was studied by experiment. The basic information of a self-developed SFRC dynamic test system matching with lnstro...The complete splitting process of steel fiber reinforced concrete （SFRC） at intermediate strain rate was studied by experiment. The basic information of a self-developed SFRC dynamic test system matching with lnstron 1342 materials testing machine was given, and the experiment principle and the loading mode of cubic split specimen were introduced. During the experiment, 30 cubes of 150 mm×150 mm×150 mm and 36 cubes of 100 mm×100 mm×100 mm, designed and prepared according to C20 class SFRC with different volume fractions of steel fiber （0, 1%, 2%, 3%, 4%） were tested and analyzed. At the same time, the size effect of SFRC at intermediate strain rate was investigated. The experimental study indicates that SFRC size effect is not influenced by the loading speed or strain rate. When the steel fiber content increases from 0 to 4%, the splitting strength of SFRC increases from 100% to 261%, i.e. increasing by 161% compared with that of the common concrete. The loading rate increases from 1.33 kN/s to 80.00 kN/s, and the splitting tensile strength increases by 43.55%.展开更多
基金supported by the National Natural Science Foundation of China[Grant Nos.51938011 and 51908405]Australian Research Council。
文摘Adopting the classical theory of hydrocodes,the constitutive relations of concretes are separated into an equation of state(EoS)which describes the volumetric behavior of concrete material and a strength model which depicts the shear properties of concrete.The experiments on the EoS of concrete is always challenging due to the technical difficulties and equipment limitations,especially for the specimen size effect on the EoS.Although some researchers investigate the shock properties of concretes by fly-plate impact tests,the specimens used in their tests are usually in one size.In this paper,the fly-plate impact tests on concrete specimens with different sizes are performed to investigate the size effect on the shock properties of concrete materials.The mechanical background of the size effect on the shock properties are revealed,which is related to the lateral rarefaction effect and the deviatoric stress produced in the specimen.According to the tests results,the modified EoS considering the size effect on the shock properties of concrete are proposed,which the bulk modulus of concrete is unpredicted by up to 20% if size effects are not accounted for.
基金the funding supports of the National Key Research and Development Plan,China(Grant No.2022YFC3801800)National Natural Science Foundation of China(Grant Nos.52038010 and 52078368)。
文摘In order to improve the overall resilience of the urban infrastructures, it is required to conduct blast resistant design for important building structures in the city. For complex terrain in the city, it is recommended to determine the blast load on the structures via numerical simulation. Since the mesh size of the numerical model highly depends on the explosion scenario, there is no generally applicable approach for the mesh size selection. An efficient method to determine the mesh size of the numerical model of near-ground detonation based on explosion scenarios is proposed in this study. The effect of mesh size on the propagation of blast wave under different explosive weights was studied, and the correlations between the mesh size effect and the charge weight or the scaled distance was described. Based on the principle of the finite element method and Hopkinson-Cranz scaling law, a mesh size measurement unit related to the explosive weight was proposed as the criterion for determining the mesh size in the numerical simulation. Finally, the applicability of the method proposed in this paper was verified by comparing the results from numerical simulation and the explosion tests and was verified in AUTODYN.
基金Project(2023YFC2907403)supported by the National Key R&D Program of ChinaProject(52074021)supported by the National Natural Science Foundation of China+1 种基金Project(2242045)supported by Beijing Natural Science Foundation,ChinaProject(ZD202216)supported by the Beijing Association of Higher Education,China。
文摘The macroscopic mechanical properties of rocks are significantly influenced by their microstructure.As a material bonded by mineral grains,the grain morphology of crystalline rock is the primary factor influencing the strength.However,most strength criteria neglect the strength variations caused by different grain characteristics in rocks.Furthermore,the traditional linear criteria tend to overestimate tensile strength and exhibit apex singularity.To address these shortcomings,a piecewise strength criterion that considers the grain size effect has been proposed.A part of an ellipse was employed to construct the envelope of the tensive-shear region on the meridian plane,to accurately reproduce the low tensile-compressive strength ratio.Based on the analysis of experimental data,both linear and exponential modification functions that account for grain size effects were integrated into the proposed criterion.The corresponding finite element algorithm has been implemented.The accuracy and applicability of the proposed criterion were validated by comparing with the experimental data.
基金Project(2012JQ7013)supported by the Natural Science Foundation of Shaanxi Province,ChinaProject(QN2012025)supported by the Fundamental Research Funds for the Central Universities of ChinaProject(2011BSJJ084)supported by Research Foundation of Northwest A&F University,China
文摘Deformation characteristics of light weight soil with different EPS (expanded polystyrene) sizes were investigated by consolidation tests.The results show that the confined stress-strain relation curve is in S shape,which has a good homologous relation with e-p curve and e-lgp curve,and three types of curves reflect obvious structural characteristics of light weight soil.When cement mixed ratio and EPS volume ratio are the same for different specimens,structural strength decreases with the increase of EPS size,but compressibility indexes basically keep unchanged within the structural strength.The settlement of light weight soil can be divided into instantaneous settlement and primary consolidation settlement.It has no obvious rheology property,and 90% of total consolidation deformation can be finished in 1 min.Settlement-time relation of light weight soil can be predicted by the hyperbolic model.S-lgt curve of light weight soil is not in anti-S shape.It is proved that there is no secondary consolidation section,so consolidation coefficient cannot be obtained by time logarithm method.Structural strength and unit price decrease with the increase of EPS size,but the reducing rate of the structural strength is lower than that of the unit price,so the cost of mixed soil can be reduced by increasing the EPS size.The EPS beads with 3-5 mm in diameter are suggested to be used in the construction process,and the prescription of mixed soil can be optimized.
基金Project(50838001) supported by the National Natural Science Foundation of China
文摘In order to investigate the size effect and other effects on the stress-strain relationship of confined concrete, 42 specimens with different sizes and section shapes were placed under axial compression loading. Effects of key parameters such as size of specimens, tie configuration, transverse reinforcement ratio, and concrete cover were studied. The results show that for specimens with the same configuration and the same volumetric ratio of the transverse reinforcement, along with the increasing specimen size, the peak stress, peak strain and deformation of the post-peak show a down trend, however, the volumetric ratio of the transverse reinforcement is lowered, the decreasing of the peak stress is accelerated, but the decreasing of the deformation is slow down. For specimens with the same volumetric ratio but different configurations of transverse reinforcement, though the transverse reinforcement configuration becomes more complicated, the peak stress of the large size specimen does not improve more than that of the small size. However, the deformation occurs before the stress declines to 85% of peak stress, and the improvement with the grid pattern tie configuration is much greater due to size effect.
基金Project(2013CB036003)supported by the National Key Basic Research Program of ChinaProjects(51374198,51134001)supported by the National Natural Science Foundation of ChinaProject(CXZZ13_0935)supported by the Jiangsu Province Ordinary College Graduate Research Innovative Program,China
文摘Uniaxial compression tests on sandstone samples with five different sizes after high temperature processes were performed in order to investigate the size effect and its evolution. The test results show that the density, longitudinal wave velocity, peak strength, average modulus and secant modulus of sandstone decrease with the increase of temperature, however, peak strain increases gradually. With the increase of ratio of height to diameter, peak strength of sandstone decreases, which has an obvious size effect. A new theoretical model of size effect of sandstone material considering the influence of temperature is put forward, and with the increase of temperature, the size effect is more apparent. The threshold decreases gradually with the increase of temperature, and the deviations of the experimental values and the theoretical values are between 0.44% and 6.06%, which shows quite a credibility of the theoretical model.
基金Project(51408213)supported by the National Natural Science Foundation of China
文摘A series of compression tests were conducted on 150 groups of cement paste specimens with side lengths ranging from 40 mm to 200 mm. The specimens include cube specimens and prism specimens with height to width ratio of 2. The experiment results show that size effect exists in the cubic compressive strength and prismatic compressive strength of the cement paste, and larger specimens resist less in terms of strength than smaller ones. The cubic compressive strength and the prismatic compressive strength of the specimens with side length of 200 mm are respectively about 91% and 89% of the compressive strength of the specimens with the side length of 40 mm. Water to binder ratio has a significant influence on the size effect of the compressive strengths of the cement paste. With a decrease in the water to binder ratio, the size effect is significantly enhanced. When the water to binder ratio is 0.2, the size effects of the cubic compressive strength and the prismatic compressive strength of the cement paste are 1.6 and 1.4 times stronger than those of a water to binder ratio of 0.6. Furthermore, a series of formulas are proposed to calculate the size effect of the cubic compressive strength and the prismatic compressive strength of cement paste, and the results of the size effect predicted by the formulas are in good agreement with the experiment results.
基金Project(51975167)supported by the National Natural Science Foundation of China。
文摘In order to gain a deeper understanding of the effect of pulsed current on the mechanical properties and size effect of nanocrystalline Ni foils,nanocrystalline Ni foils with different grain thickness-to-grain size ratios(λ)were prepared using pulsed electrodeposition in this paper and unidirectional tensile experiments were carried out at room temperature with different currents and their applied directions.The experimental results show that the nanocrystalline Ni foil produces an obvious electroplasticity effect after applying the current field,and when 300<λ<1100,the current weakens the size effect of nanocrystalline Ni foils to a certain extent,and the angle between the current direction and the deformation direction also affects the mechanical response of nanocrystalline Ni foils,and when the angle between the current direction and the deformation direction is 0°,electroplasticity effect is the best,and the current has the most significant effect of abating the size effect of the material.The mechanism of unidirectional tensile deformation of nanocrystalline Ni foils under the effect of pulsed current was analyzed using TEM and TKD.It was found that the applied pulse current increased the activity of the nanocrystalline boundaries,promoted the movement of dislocations,and reduced the tendency of dislocation entanglement.The higher the peak current density and the smaller the angle between the direction of the current and the direction of deformation,the smaller the grain boundary orientation difference,the more dispersed the grain orientation,and the lower the density of geometrically necessary dislocations(GND)in the deformed nanocrystalline foil,the more significant the effect on material plasticity improvement.
基金Projects(51176029,50876020) supported by the National Natural Science Foundation of ChinaProject(2011BAJ03B00) supported by the 12th Five-Year National Science and Technology Support Key Program of China Project(ybjj1124) supported by the Foundation of Graduate School of Southeast University,China
文摘In order to investigate the mechanism of nanoparticles enhancing the heat and mass transfer of the ammonia-water absorption process,several types of binary nanofluids were prepared by mixing Al2O3 nanoparticles with polyacrylic acid(PAA),TiO2 with polyethylene glycol(PEG 1000),and TiN,SiC,hydroxyapatite(noodle-like) with PEG 10000 to ammonia-water solution,respectively.The thermal conductivities were measured by using a KD2 Pro thermal properties analyzer.The influences of surfactant and ammonia on the dispersion stabilities of the binary nanofluids were investigated by the light absorbency ratio index methods.The results show that the type,content and size of nanoparticles,the temperature as well as the dispersion stability are the key parameters that affect the thermal conductivity of nanofluids.For the given nanoparticle material and the base fluid,the thermal conductivity ratio of the nanofluid to the ammonia-water liquid increases as the nanoparticle content and the temperature are increased,and the diameter of nanoparticle is decreased.Furthermore,the thermal conductivity ratio increases significantly by improving the stabilities of nanofluids,which is achieved by adding surfactants or performing the proper ammonia content in the fluid.
文摘The complete splitting process of steel fiber reinforced concrete （SFRC） at intermediate strain rate was studied by experiment. The basic information of a self-developed SFRC dynamic test system matching with lnstron 1342 materials testing machine was given, and the experiment principle and the loading mode of cubic split specimen were introduced. During the experiment, 30 cubes of 150 mm×150 mm×150 mm and 36 cubes of 100 mm×100 mm×100 mm, designed and prepared according to C20 class SFRC with different volume fractions of steel fiber （0, 1%, 2%, 3%, 4%） were tested and analyzed. At the same time, the size effect of SFRC at intermediate strain rate was investigated. The experimental study indicates that SFRC size effect is not influenced by the loading speed or strain rate. When the steel fiber content increases from 0 to 4%, the splitting strength of SFRC increases from 100% to 261%, i.e. increasing by 161% compared with that of the common concrete. The loading rate increases from 1.33 kN/s to 80.00 kN/s, and the splitting tensile strength increases by 43.55%.
