Particle morphology has been regarded as an important factor affecting shear behaviors of sands,and covers three important aspects,i.e.global form(overall shape),local roundness(large-scale smoothness),and surface tex...Particle morphology has been regarded as an important factor affecting shear behaviors of sands,and covers three important aspects,i.e.global form(overall shape),local roundness(large-scale smoothness),and surface texture(roughness)in terms of different observation scales.Shape features of different aspects can be independent of each other but might have coupled effects on the bulk behavior of sands,which has been not explored thoroughly yet.This paper presents a systematic investigation of the coupled effects of the particle overall regularity(OR)and sliding friction on the shear behavior of dense sands using three-dimensional(3D)discrete element method(DEM).The representative volume elements consisting of ideal spheres and irregular clumps of different mass proportions are prepared to conduct drained triaxial compression simulations.A well-defined shape descriptor named OR is adopted to quantify particle shape differences of numerical samples at both form and roundness aspects,and the particle sliding friction coefficient varies from 0.001 to 1 to consider the surface roughness effect equivalently in DEM.The stress-strain relationships as well as peak and critical friction angles of these assemblies are examined systematically.Moreover,contact network and anisotropic fabric characteristics within different granular assemblies are analyzed to explore the microscopic origins of the multi-scale shape-dependent shear strength.This study helps to improve the current understanding with respect to the influence of the particle shape on the shear behavior of sands from different shape aspects.展开更多
The effect of La addition in Fe-P-N upon Snoek-Ke-Kster(SKK)damping peak was studied.It was found that the damping depends on the atomic concentration ratio between La and P(C_(La)/C_P).When the ratio is comparatively...The effect of La addition in Fe-P-N upon Snoek-Ke-Kster(SKK)damping peak was studied.It was found that the damping depends on the atomic concentration ratio between La and P(C_(La)/C_P).When the ratio is comparatively high in the alloy(for example,4.56 on 2.6),La will appreciably enhance SKK damping,whereas in the alloy saturated with P at a lower C_(La)/C_P ratio of 0.27 La will no longer exert any effect on SKK peak.展开更多
The friction peak that occurs in tire–road sliding when the contact changes from wet to dry was previously attributed to capillary cohesion,van der Waals attraction,and surface roughness,but the detailed mechanisms h...The friction peak that occurs in tire–road sliding when the contact changes from wet to dry was previously attributed to capillary cohesion,van der Waals attraction,and surface roughness,but the detailed mechanisms have yet to be revealed.In this study,friction and static contact experiments were conducted using a custom-built in situ optical microtribometer,which allowed us to investigate the evolution of the friction,normal load,and contact area between a polydimethylsiloxane(PDMS)film and a silicon nitride ball during water volatilization.The friction coefficient increased by 100%,and the normal force dropped by 30%relative to those in the dry condition during the wet-to-dry transition.In static contact experiments,the probe indentation depth increased,and the normal load decreased by~60%as the water evaporated.Combining the friction and static contact results,we propose that the large friction peak that appeared in this study can be attributed to the combined effects of increased adhesive capillary force and increased plowing during the wet-to-dry transition.展开更多
Internal friction and modulus measurements of nano ZrO_2 solids for different particle sizes (including original compacted and annealed samples) were systematically carried out from room temperature to -200℃. It was ...Internal friction and modulus measurements of nano ZrO_2 solids for different particle sizes (including original compacted and annealed samples) were systematically carried out from room temperature to -200℃. It was found that the three peaks (P_1, P_2 and P_3 corresponding to ascending measurement, or P_1~', P_2~' and P_3~' corresponding to descending measurement) appeared. By investigating the behavior of internal friction peaks (P_1, P_2, P_3 orP_1~' P_2~', P_3~'), it is indicated that the origin of peak P_3 or P_3~' can be attributed to grain boundary relaxation, that is, it is caused by slip of the grain boundaries in nano ZrO_2 solids. The peak P_2 (or P_2~')and P_1 (or P_1~') may possibly be associated with phase transformation of nano ZrO_2 solids at low temperature range. The energy dispersion decreases and the modulus increases notably with the increase in annealing temperature of the nano samples.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 42077238 and 41941019)the Guangdong Basic and Applied Basic Research Foundation, China (Grant No. 2020A1515011525)
文摘Particle morphology has been regarded as an important factor affecting shear behaviors of sands,and covers three important aspects,i.e.global form(overall shape),local roundness(large-scale smoothness),and surface texture(roughness)in terms of different observation scales.Shape features of different aspects can be independent of each other but might have coupled effects on the bulk behavior of sands,which has been not explored thoroughly yet.This paper presents a systematic investigation of the coupled effects of the particle overall regularity(OR)and sliding friction on the shear behavior of dense sands using three-dimensional(3D)discrete element method(DEM).The representative volume elements consisting of ideal spheres and irregular clumps of different mass proportions are prepared to conduct drained triaxial compression simulations.A well-defined shape descriptor named OR is adopted to quantify particle shape differences of numerical samples at both form and roundness aspects,and the particle sliding friction coefficient varies from 0.001 to 1 to consider the surface roughness effect equivalently in DEM.The stress-strain relationships as well as peak and critical friction angles of these assemblies are examined systematically.Moreover,contact network and anisotropic fabric characteristics within different granular assemblies are analyzed to explore the microscopic origins of the multi-scale shape-dependent shear strength.This study helps to improve the current understanding with respect to the influence of the particle shape on the shear behavior of sands from different shape aspects.
文摘The effect of La addition in Fe-P-N upon Snoek-Ke-Kster(SKK)damping peak was studied.It was found that the damping depends on the atomic concentration ratio between La and P(C_(La)/C_P).When the ratio is comparatively high in the alloy(for example,4.56 on 2.6),La will appreciably enhance SKK damping,whereas in the alloy saturated with P at a lower C_(La)/C_P ratio of 0.27 La will no longer exert any effect on SKK peak.
基金The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China(Nos.51875152,51875153,and 51975174).
文摘The friction peak that occurs in tire–road sliding when the contact changes from wet to dry was previously attributed to capillary cohesion,van der Waals attraction,and surface roughness,but the detailed mechanisms have yet to be revealed.In this study,friction and static contact experiments were conducted using a custom-built in situ optical microtribometer,which allowed us to investigate the evolution of the friction,normal load,and contact area between a polydimethylsiloxane(PDMS)film and a silicon nitride ball during water volatilization.The friction coefficient increased by 100%,and the normal force dropped by 30%relative to those in the dry condition during the wet-to-dry transition.In static contact experiments,the probe indentation depth increased,and the normal load decreased by~60%as the water evaporated.Combining the friction and static contact results,we propose that the large friction peak that appeared in this study can be attributed to the combined effects of increased adhesive capillary force and increased plowing during the wet-to-dry transition.
基金Project supported by Laboratory of Internal Friction and Defects in Solids, Academia Sinica
文摘Internal friction and modulus measurements of nano ZrO_2 solids for different particle sizes (including original compacted and annealed samples) were systematically carried out from room temperature to -200℃. It was found that the three peaks (P_1, P_2 and P_3 corresponding to ascending measurement, or P_1~', P_2~' and P_3~' corresponding to descending measurement) appeared. By investigating the behavior of internal friction peaks (P_1, P_2, P_3 orP_1~' P_2~', P_3~'), it is indicated that the origin of peak P_3 or P_3~' can be attributed to grain boundary relaxation, that is, it is caused by slip of the grain boundaries in nano ZrO_2 solids. The peak P_2 (or P_2~')and P_1 (or P_1~') may possibly be associated with phase transformation of nano ZrO_2 solids at low temperature range. The energy dispersion decreases and the modulus increases notably with the increase in annealing temperature of the nano samples.
