To disclose the grain crushing effects on the weathered granular soil rheological behavior,a series of rheological tests (odometer compression and triaxial shearing) were carried out.At the same time,the sieving analy...To disclose the grain crushing effects on the weathered granular soil rheological behavior,a series of rheological tests (odometer compression and triaxial shearing) were carried out.At the same time,the sieving analysis tests of these specimens were also executed before and after tests,and the grain crushing degree,Br and n5,were collectively adopted to estimate the grain crushing.The grain crushing degree depends on the stress path,stress level,and load time,especially,the longer load time and more intensive gradient shearing path will increase the grain crushing quantity.The Hardin crushing degrees Br are 0.191,0.118 and 0.085 in the ordinary compression,rheological compression and triaxial rheological shearing,respectively;The grain crushing degrees n5 are 1.9,1.4 and 1.32,respectively.The strain softening phase indicates the grain crushing and diffusive collapse,and the strain hardening phase indicates the rearrangement of these crushed grains and formation of new bearing soil skeleton.The rheological deformation of granular soil can be attributed to the coarse grain crushing and the filling external porosity with crushed fragments.展开更多
The mechanical behavior of sand is very complex, and depends on factors including confining pressure, density, and drainage condition. A soil mass can be contractive or dilative when subjected to shear loading, and ev...The mechanical behavior of sand is very complex, and depends on factors including confining pressure, density, and drainage condition. A soil mass can be contractive or dilative when subjected to shear loading, and eventually reaches an ultimate state, referred to as the critical state in soil mechanics. Conventional approach to explore the mechanical behavior of sand mainly relies on the experimental tests in laboratory. This paper gives an alternative view to this subject using discrete element method (DEM), which has attracted much attention in recent years. The implementation of the DEM is carried out by a series of numerical tests on granular assemblies with varying initial densities and confining pressures, under different test configurations. The results demonstrate that such numerical simulations can produce correct responses of the sand behavior in general, including the critical state response, as compared to experimental observations. In addition, the DEM can further provide details of the microstructure evolutions during shearing processes, and the resulting induced anisotropy can be fully captured and quantified in the particle scale.展开更多
The impact energy decay in a step-up chain containing two sections is numerically studied.There is a marked biphasic behavior of energy decay in the first section.Two sections close to the interface are in compression...The impact energy decay in a step-up chain containing two sections is numerically studied.There is a marked biphasic behavior of energy decay in the first section.Two sections close to the interface are in compression state.The degree of compression of the first section first decreases and becomes weakest at ＂crossing＂ time of biphasic behavior of energy,then increases.The further calculations provide the dependence of the character time on mass ratio（m1/m2）,where m1 and m2are the particle mass in the first and second section respectively.The bigger the α（α = [（？ m1-m2）/（？ m1＋ m2）]2 with？ = 1.345）,the bigger the energy ratio is.The multipulse structure restricts the transport of energy.展开更多
The vesicant problem during the process of preparing closed-cell aluminum foam by molten body transitional foaming process was discussed and the effect of granularity and addition of TiH2on porosity of closed-cell alu...The vesicant problem during the process of preparing closed-cell aluminum foam by molten body transitional foaming process was discussed and the effect of granularity and addition of TiH2on porosity of closed-cell aluminum foam was investigated. The static compressive behavior of closed-cell aluminum foam and the influence of porosity on static compressive property of closed-cell aluminum foam were researched as well. The results show that with increasing granularity of TiH2,the porosity of closed-cell aluminum foam firstly increases and then decreases gradually, the granularity should be controlled in the range of 38-74μm which can result in higher porosity. The porosity of closed-cell aluminum foam increases with the increasing addition of TiH2, and the addition of TiH2 should be controlled from 1.5% to 2.5% which can result in homogeneous cell and moderate strength of closed-cell aluminum foam. The compressive process of closed-cell aluminum foam obviously displays linear elastic phase, plastic collapse phase, and densification phase, and the compressive strength grows with decreasing porosity.展开更多
Granular precipitate that was a new kind ofβ-Mg17Al12 phase found in aged AZ80 wrought Mg alloy at all aging temperature was studied. The structure and precipitation behavior of this granularβ-Mg17Al12 precipitate w...Granular precipitate that was a new kind ofβ-Mg17Al12 phase found in aged AZ80 wrought Mg alloy at all aging temperature was studied. The structure and precipitation behavior of this granularβ-Mg17Al12 precipitate were studied by environmental scanning electron microscopy (ESEM) and transmission electron microscopy (TEM). The effect of the granular precipitate on mechanical properties of AZ80 alloy was also studied. The new precipitate that was granular and nucleated both on grain boundaries (GBs) and twin boundaries, has the same crystal structure and lattice parameter as those of the continuous or discontinuous precipitatedβ-Mg17Al12. And the nucleation and growth of the granular precipitate are faster than those of the other two precipitates at higher temperatures (above 583 K), but are suppressed at lower temperatures (below 423 K). At lower temperatures, the discontinuousβ-Mg17Al12 precipitates firstly and the granularβ-Mg17Al12 precipitates after aged more than 40 h. The crack is easily nucleated on the phase boundaries of granular phase and matrix because of the weak binding force. As a result, the strength and ductility of AZ80 Mg alloy are decreased by the granularyβ-Mg17Al12 precipitate.展开更多
The resilient modulus (Mr) is an important parameter which describes the mechanical behavior of unbound granular materials. However, this parameter can be determined from physical properties. This paper presents the r...The resilient modulus (Mr) is an important parameter which describes the mechanical behavior of unbound granular materials. However, this parameter can be determined from physical properties. This paper presents the relationship between resilient modulus and physical properties of Quartzite from Bakel (GB), Basalt from Diack and Bargny and Bandia limestones. Simple and multiple regression method by stepwise are used to establish linear and nonlinear relations to predict the resilient modulus. The results showed no significant correlation for Basalt, a weak estimation of the modulus for GB and good prediction of resilient modulus for limestone. These results also showed that the model of Uzan is more suitable to predict the resilient modulus than NCHRP model and the resilient modulus is better predicted in nonlinear relationship.展开更多
基金Project(50908233) supported by the National Natural Science Foundation of ChinaProject(200413) supported by Communication Science and Technology Fund of Hunan Province,China
文摘To disclose the grain crushing effects on the weathered granular soil rheological behavior,a series of rheological tests (odometer compression and triaxial shearing) were carried out.At the same time,the sieving analysis tests of these specimens were also executed before and after tests,and the grain crushing degree,Br and n5,were collectively adopted to estimate the grain crushing.The grain crushing degree depends on the stress path,stress level,and load time,especially,the longer load time and more intensive gradient shearing path will increase the grain crushing quantity.The Hardin crushing degrees Br are 0.191,0.118 and 0.085 in the ordinary compression,rheological compression and triaxial rheological shearing,respectively;The grain crushing degrees n5 are 1.9,1.4 and 1.32,respectively.The strain softening phase indicates the grain crushing and diffusive collapse,and the strain hardening phase indicates the rearrangement of these crushed grains and formation of new bearing soil skeleton.The rheological deformation of granular soil can be attributed to the coarse grain crushing and the filling external porosity with crushed fragments.
基金the National Natural Science Foundation of China (Nos. 10725210 and 50509021)the Postdoctoral Foundations in China (No. 20070421202)+1 种基金the Program for New Century Excellent Talents in University in China (No. NCET-05-05010)the Com-petitive Postdoctoral Research Project in Zhejiang Province, China
文摘The mechanical behavior of sand is very complex, and depends on factors including confining pressure, density, and drainage condition. A soil mass can be contractive or dilative when subjected to shear loading, and eventually reaches an ultimate state, referred to as the critical state in soil mechanics. Conventional approach to explore the mechanical behavior of sand mainly relies on the experimental tests in laboratory. This paper gives an alternative view to this subject using discrete element method (DEM), which has attracted much attention in recent years. The implementation of the DEM is carried out by a series of numerical tests on granular assemblies with varying initial densities and confining pressures, under different test configurations. The results demonstrate that such numerical simulations can produce correct responses of the sand behavior in general, including the critical state response, as compared to experimental observations. In addition, the DEM can further provide details of the microstructure evolutions during shearing processes, and the resulting induced anisotropy can be fully captured and quantified in the particle scale.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61174007 and 61307041)the Natural Science Foundation of Shandong Province,China(Grant No.ZR2013AL014)
文摘The impact energy decay in a step-up chain containing two sections is numerically studied.There is a marked biphasic behavior of energy decay in the first section.Two sections close to the interface are in compression state.The degree of compression of the first section first decreases and becomes weakest at ＂crossing＂ time of biphasic behavior of energy,then increases.The further calculations provide the dependence of the character time on mass ratio（m1/m2）,where m1 and m2are the particle mass in the first and second section respectively.The bigger the α（α = [（？ m1-m2）/（？ m1＋ m2）]2 with？ = 1.345）,the bigger the energy ratio is.The multipulse structure restricts the transport of energy.
基金Project (2002AA334060) supported by the Hi-tech Research and Development Program of China
文摘The vesicant problem during the process of preparing closed-cell aluminum foam by molten body transitional foaming process was discussed and the effect of granularity and addition of TiH2on porosity of closed-cell aluminum foam was investigated. The static compressive behavior of closed-cell aluminum foam and the influence of porosity on static compressive property of closed-cell aluminum foam were researched as well. The results show that with increasing granularity of TiH2,the porosity of closed-cell aluminum foam firstly increases and then decreases gradually, the granularity should be controlled in the range of 38-74μm which can result in higher porosity. The porosity of closed-cell aluminum foam increases with the increasing addition of TiH2, and the addition of TiH2 should be controlled from 1.5% to 2.5% which can result in homogeneous cell and moderate strength of closed-cell aluminum foam. The compressive process of closed-cell aluminum foam obviously displays linear elastic phase, plastic collapse phase, and densification phase, and the compressive strength grows with decreasing porosity.
基金Project (2001AA331050) supported by the Hi-Tech Research And Development Program Of China
文摘Granular precipitate that was a new kind ofβ-Mg17Al12 phase found in aged AZ80 wrought Mg alloy at all aging temperature was studied. The structure and precipitation behavior of this granularβ-Mg17Al12 precipitate were studied by environmental scanning electron microscopy (ESEM) and transmission electron microscopy (TEM). The effect of the granular precipitate on mechanical properties of AZ80 alloy was also studied. The new precipitate that was granular and nucleated both on grain boundaries (GBs) and twin boundaries, has the same crystal structure and lattice parameter as those of the continuous or discontinuous precipitatedβ-Mg17Al12. And the nucleation and growth of the granular precipitate are faster than those of the other two precipitates at higher temperatures (above 583 K), but are suppressed at lower temperatures (below 423 K). At lower temperatures, the discontinuousβ-Mg17Al12 precipitates firstly and the granularβ-Mg17Al12 precipitates after aged more than 40 h. The crack is easily nucleated on the phase boundaries of granular phase and matrix because of the weak binding force. As a result, the strength and ductility of AZ80 Mg alloy are decreased by the granularyβ-Mg17Al12 precipitate.
文摘The resilient modulus (Mr) is an important parameter which describes the mechanical behavior of unbound granular materials. However, this parameter can be determined from physical properties. This paper presents the relationship between resilient modulus and physical properties of Quartzite from Bakel (GB), Basalt from Diack and Bargny and Bandia limestones. Simple and multiple regression method by stepwise are used to establish linear and nonlinear relations to predict the resilient modulus. The results showed no significant correlation for Basalt, a weak estimation of the modulus for GB and good prediction of resilient modulus for limestone. These results also showed that the model of Uzan is more suitable to predict the resilient modulus than NCHRP model and the resilient modulus is better predicted in nonlinear relationship.
