Gravity is the most important load source in mining and geotechnical engineering,which causes both the stress level and stress gradient inside geomaterials.Different from the stress level,the influence of gravity-indu...Gravity is the most important load source in mining and geotechnical engineering,which causes both the stress level and stress gradient inside geomaterials.Different from the stress level,the influence of gravity-induced stress gradient on the behaviour of the material is still unknown.An in-deep study on it will help to promote the understanding of material behaviour,especially for those cases related to unconventional gravity such as terrestrial ng physical modelling and extraterrestrial resource exploitation(g is the terrestrial gravitational acceleration).In this study,a high-order homogenization for granular materials is proposed at first,in which the stress gradient is drawn into the constitutive representation by adopting a representative volume element(RVE).The consolidation and shear strength behaviour of RVE are then investigated by performing numerical biaxial tests.The results show that all the compressibility,shear strength,shear stiffness,volumetric deformation,and critical state behaviour show a stress gradient dependence.A coupling between stress gradient,stress level,and material properties is also observed.These observations suggest that,besides the stress level,extra attention needs to be paid to material responses related to stress gradient during engineering practices.展开更多
Multi-scale finite element method is adopted to simulate wood compression behavior under axial and transverse loading. Representative volume elements (RVE) of wood microfibril and cell are proposed to analyze orthotro...Multi-scale finite element method is adopted to simulate wood compression behavior under axial and transverse loading. Representative volume elements (RVE) of wood microfibril and cell are proposed to analyze orthotropic mechanical behavior. Lignin, hemicellulose and crystalline-amorphous cellulose core of spruce are concerned in spruce nanoscale model. The equivalent elastic modulus and yield strength of the microfibril are gained by the RVE simulation. The anisotropism of the crystalline-amorphous cellulose core brings the microfibril buckling deformation during compression loading. The failure mechanism of the cell-wall under axial compression is related to the distribution of amorphous cellulose and crystalline cellulose. According to the spruce cell observation by scanning electron microscope, numerical model of spruce cell is established using simplified circular hole and regular hexagon arrangement respectively. Axial and transverse compression loadings are taken into account in the numerical simulations. It indicates that the compression stress-strain curves of the numerical simulation are consistent with the experimental results. The wood microstructure arrangement has an important effect on the stress plateau during compression process. Cell-wall buckling in axial compression induces the stress value drops rapidly. The wide stress plateau duration means wood is with large energy dissipation under a low stress level. The numerical results show that loading velocity affects greatly wood microstructure failure modes in axial loading. For low velocity axial compression, shear sliding is the main failure mode. For high velocity axial compression, wood occur fold and collapse. In transverse compression, wood deformation is gradual and uniform, which brings stable stress plateau.展开更多
基金Supported by NSFC(10572028)National Basic Research Program of China(2005CB321702)+4 种基金CAEP(2007B09009)National Hi-Tech Inertial Confinement Fusion Committee of ChinaNSF(DMS-0809086)ARO(W911NF-08-1-0520)DOE(DE-FG02-08ER25863)
基金supported by the National Natural Science Foundation of China(Nos.41902273,41772338)the China Postdoctoral Science Foundation(No.2019M661986)+2 种基金the Natural Science Foundation of Jiangsu Province(No.BK20190637)the Jiangsu Planned Projects for Postdoctoral Research Funds(No.2019K194)financial support by the State Key Laboratory for Geomechanics and Deep Underground Engineering,China University of Mining and Technology(Nos.Z19007,Z19009)。
文摘Gravity is the most important load source in mining and geotechnical engineering,which causes both the stress level and stress gradient inside geomaterials.Different from the stress level,the influence of gravity-induced stress gradient on the behaviour of the material is still unknown.An in-deep study on it will help to promote the understanding of material behaviour,especially for those cases related to unconventional gravity such as terrestrial ng physical modelling and extraterrestrial resource exploitation(g is the terrestrial gravitational acceleration).In this study,a high-order homogenization for granular materials is proposed at first,in which the stress gradient is drawn into the constitutive representation by adopting a representative volume element(RVE).The consolidation and shear strength behaviour of RVE are then investigated by performing numerical biaxial tests.The results show that all the compressibility,shear strength,shear stiffness,volumetric deformation,and critical state behaviour show a stress gradient dependence.A coupling between stress gradient,stress level,and material properties is also observed.These observations suggest that,besides the stress level,extra attention needs to be paid to material responses related to stress gradient during engineering practices.
基金supported by the National Natural Science Foundation of China(Grants Nos 11302211,11390361,and 11572299).
文摘Multi-scale finite element method is adopted to simulate wood compression behavior under axial and transverse loading. Representative volume elements (RVE) of wood microfibril and cell are proposed to analyze orthotropic mechanical behavior. Lignin, hemicellulose and crystalline-amorphous cellulose core of spruce are concerned in spruce nanoscale model. The equivalent elastic modulus and yield strength of the microfibril are gained by the RVE simulation. The anisotropism of the crystalline-amorphous cellulose core brings the microfibril buckling deformation during compression loading. The failure mechanism of the cell-wall under axial compression is related to the distribution of amorphous cellulose and crystalline cellulose. According to the spruce cell observation by scanning electron microscope, numerical model of spruce cell is established using simplified circular hole and regular hexagon arrangement respectively. Axial and transverse compression loadings are taken into account in the numerical simulations. It indicates that the compression stress-strain curves of the numerical simulation are consistent with the experimental results. The wood microstructure arrangement has an important effect on the stress plateau during compression process. Cell-wall buckling in axial compression induces the stress value drops rapidly. The wide stress plateau duration means wood is with large energy dissipation under a low stress level. The numerical results show that loading velocity affects greatly wood microstructure failure modes in axial loading. For low velocity axial compression, shear sliding is the main failure mode. For high velocity axial compression, wood occur fold and collapse. In transverse compression, wood deformation is gradual and uniform, which brings stable stress plateau.
