For the Guanshui Road Station tunnel project of Guiyang Metro Line 2,the wind pavilion group was moved out of the main tunnel to reduce the number of openings in the main tunnel,and the wind pavilion group was excavat...For the Guanshui Road Station tunnel project of Guiyang Metro Line 2,the wind pavilion group was moved out of the main tunnel to reduce the number of openings in the main tunnel,and the wind pavilion group was excavated in a triangular configuration at the entrance of the main tunnel.Based on the finite element software ABAQUS,a three-dimensional model is established to study the influence of different triangular-distribution tunnels excavation schemes on the surface settlement and tunnel stability.The objective of this study is to reveal the change rules of surface settlement,deformation and force in the support structures and the surrounding rock and identify the best excavation scheme for this tunnel configuration.Results show that to control the surface settlement and the deformation of the support structures,the optimal excavation sequence involves excavating the upper fresh air exhaust tunnel before the lower running tunnel.To control the stress of the support structures,the optimal excavation involves excavating the lower running tunnel before the upper fresh air exhaust tunnel.In this project,the most reasonable excavation sequence of the tunnel is from top to bottom.The most reasonable thickness of tunnel penetration is 5 m.展开更多
Based on the nonlinear Mohr-Coulomb failure criterion and the associated flow rules,the three-dimensional(3-D)axisymmetric failure mechanism of shallow horizontal circular plate anchors that are subjected to the ultim...Based on the nonlinear Mohr-Coulomb failure criterion and the associated flow rules,the three-dimensional(3-D)axisymmetric failure mechanism of shallow horizontal circular plate anchors that are subjected to the ultimate pullout capacity(UPC)is determined.A derivative function of the projection function for projecting the 3-D axisymmetric failure surface on plane is deduced using the variation theory.By using difference principle,the primitive function of failure surface satisfying boundary condition and numerical solution to its corresponding ultimate pullout capacity function are obtained.The influences of nonlinear Mohr-Coulomb parameters on UPC and failure mechanism are studied.The result shows that UPC decreases with dimensionless parameter m and uniaxial tensile strength increases but increases when depth and radius of plate anchor,surface overload,initial cohesion,geomaterial density and friction angle increase.The failure surface is similar to a symmetrical spatial funnel,and its shape is mainly determined by dimensionless parameter m;the surface damage range expands with the increase of radius and depth of the plate anchor as well as initial cohesion but decreases with the increase of dimensionless parameter m and uniaxial tensile strength as well as geomaterial density.As the dimensionless parameter m=2.0,the numerical solution of UPC based on the difference principle is proved to be feasible and effective through the comparison with the exact solution.In addition,the comparison between solutions of UPC computed by variation method and those computed by upper bound method indicate that variation method outperforms upper bound method.展开更多
In this study,the effect of influencing parameters on the stress distribution around a polygonal cutout within a laminated composite under uniform heat flux was analytically examined.The analytical method was develope...In this study,the effect of influencing parameters on the stress distribution around a polygonal cutout within a laminated composite under uniform heat flux was analytically examined.The analytical method was developed based on the classical laminated plate theory and two-dimensional thermo-elastic method.A mapping function was employed to extend the solution of a perforated symmetric laminate with a circular cutout to the solution of polygonal cutouts.The effect of significant parameters such as the cutout angular position,bluntness and aspect ratio,the heat flux angle and the laminate stacking sequence in symmetric composite laminate containing triangular,square and pentagonal cutouts was studied.The Neumann boundary condition was used at the edges of the thermally insulated polygonal cutout.The laminate was made of graphite/epoxy(AS/3501) material with two different stacking sequences of [30/45]sand[30/0/-30]_(s).The analytical solutions were well validated against finite element results.展开更多
The drawn copper wires have been analyzed by differential scanning calorimeter(DSC) and a new method, which uses DSC measurements to determine the Johnson-Mehl-Avrami-Kolmogorov(JMAK) exponent via introducing Arrheniu...The drawn copper wires have been analyzed by differential scanning calorimeter(DSC) and a new method, which uses DSC measurements to determine the Johnson-Mehl-Avrami-Kolmogorov(JMAK) exponent via introducing Arrhenius behavior and modifying the baseline of DSC curves, has been proposed. The results show that JMAK exponent and recrystallization activation energy of the drawn copper wires with a strain of 2.77 are about 2.39 and 125 k J/mol, respectively. The line linking the tangency points of DSC curve hypotenuse can be used as the baseline when calculating recrystallization fraction. The JMAK exponent obtained by the DSC method is in a good agreement with that obtained by microhardness measurements. Compared to traditional methods to measure the exponent, the proposed method is faster and less labor intensive.展开更多
基金Projects(B200204032,2019B07914)supported by the Fundamental Research Funds for the Central Universities,ChinaProjects(51878667,51678571,51808193)supported by the National Natural Science Foundation of China。
文摘For the Guanshui Road Station tunnel project of Guiyang Metro Line 2,the wind pavilion group was moved out of the main tunnel to reduce the number of openings in the main tunnel,and the wind pavilion group was excavated in a triangular configuration at the entrance of the main tunnel.Based on the finite element software ABAQUS,a three-dimensional model is established to study the influence of different triangular-distribution tunnels excavation schemes on the surface settlement and tunnel stability.The objective of this study is to reveal the change rules of surface settlement,deformation and force in the support structures and the surrounding rock and identify the best excavation scheme for this tunnel configuration.Results show that to control the surface settlement and the deformation of the support structures,the optimal excavation sequence involves excavating the upper fresh air exhaust tunnel before the lower running tunnel.To control the stress of the support structures,the optimal excavation involves excavating the lower running tunnel before the upper fresh air exhaust tunnel.In this project,the most reasonable excavation sequence of the tunnel is from top to bottom.The most reasonable thickness of tunnel penetration is 5 m.
基金Project(51478477)supported by the National Natural Science Foundation of ChinaProject(2016CX012)supported by the Innovation-driven Project of Central South University,ChinaProject(2014122006)supported by the Guizhou Provincial Department of Transportation Foundation,China
文摘Based on the nonlinear Mohr-Coulomb failure criterion and the associated flow rules,the three-dimensional(3-D)axisymmetric failure mechanism of shallow horizontal circular plate anchors that are subjected to the ultimate pullout capacity(UPC)is determined.A derivative function of the projection function for projecting the 3-D axisymmetric failure surface on plane is deduced using the variation theory.By using difference principle,the primitive function of failure surface satisfying boundary condition and numerical solution to its corresponding ultimate pullout capacity function are obtained.The influences of nonlinear Mohr-Coulomb parameters on UPC and failure mechanism are studied.The result shows that UPC decreases with dimensionless parameter m and uniaxial tensile strength increases but increases when depth and radius of plate anchor,surface overload,initial cohesion,geomaterial density and friction angle increase.The failure surface is similar to a symmetrical spatial funnel,and its shape is mainly determined by dimensionless parameter m;the surface damage range expands with the increase of radius and depth of the plate anchor as well as initial cohesion but decreases with the increase of dimensionless parameter m and uniaxial tensile strength as well as geomaterial density.As the dimensionless parameter m=2.0,the numerical solution of UPC based on the difference principle is proved to be feasible and effective through the comparison with the exact solution.In addition,the comparison between solutions of UPC computed by variation method and those computed by upper bound method indicate that variation method outperforms upper bound method.
文摘In this study,the effect of influencing parameters on the stress distribution around a polygonal cutout within a laminated composite under uniform heat flux was analytically examined.The analytical method was developed based on the classical laminated plate theory and two-dimensional thermo-elastic method.A mapping function was employed to extend the solution of a perforated symmetric laminate with a circular cutout to the solution of polygonal cutouts.The effect of significant parameters such as the cutout angular position,bluntness and aspect ratio,the heat flux angle and the laminate stacking sequence in symmetric composite laminate containing triangular,square and pentagonal cutouts was studied.The Neumann boundary condition was used at the edges of the thermally insulated polygonal cutout.The laminate was made of graphite/epoxy(AS/3501) material with two different stacking sequences of [30/45]sand[30/0/-30]_(s).The analytical solutions were well validated against finite element results.
基金Projects(51171135,51371132,51471123) supported by the National Natural Science Foundation of ChinaProjects(2012K07-08,2013KJXX-61) supported by Key Science and Technology Program of Shaanxi Province,ChinaProject(2013JC14) supported by the Education Department Foundation of Shaanxi Province,China
文摘The drawn copper wires have been analyzed by differential scanning calorimeter(DSC) and a new method, which uses DSC measurements to determine the Johnson-Mehl-Avrami-Kolmogorov(JMAK) exponent via introducing Arrhenius behavior and modifying the baseline of DSC curves, has been proposed. The results show that JMAK exponent and recrystallization activation energy of the drawn copper wires with a strain of 2.77 are about 2.39 and 125 k J/mol, respectively. The line linking the tangency points of DSC curve hypotenuse can be used as the baseline when calculating recrystallization fraction. The JMAK exponent obtained by the DSC method is in a good agreement with that obtained by microhardness measurements. Compared to traditional methods to measure the exponent, the proposed method is faster and less labor intensive.
