The fatigue fracture under cyclic dynamic direct tensions of brittle rock is an important mechanical characteristic index for the evaluation of geological disasters and underground engineering safety.However,most stud...The fatigue fracture under cyclic dynamic direct tensions of brittle rock is an important mechanical characteristic index for the evaluation of geological disasters and underground engineering safety.However,most studies focus on macroscopic fracture mechanical properties,and the mechanism linking the macroscopic fracture with the microcrack growth during the cyclic dynamic direct tensile loading of brittle rocks is rarely studied.In this paper,a micro-macro fracture model explaining the stress-strain constitutive relationship is established at the last impact failure after being subjected to multiple cyclic direct tensile impacts of brittle rocks.This model is based on the wing crack extension model under direct tensile loading,the quasi-static and dynamic fracture toughness relationship,the suggested crack rate and strain rate relationship,the relationship of damage and dynamic tensile fatigue life N,the relationship of dynamic fracture toughness and dynamic tensile fatigue life N.The variations of dynamic mechanical properties of rocks with dynamic tensile fatigue life for different initial crack sizes and angles within the rocks are further discussed.The compressive strength,elastic modulus,crack initiation stress,limit crack extension length and crack extension rate descend and the failure strain ascends with an increment of dynamic tensile fatigue life in rocks.This study's results provide help for the safety and stability of the underground surrounding rocks under blasting working or seismic disasters.展开更多
This article presents a micro-macro unified model for predicting the deformation of metal matrix composites （MMCs）. A macro-scale model is developed to obtain the proper boundary conditions for the micro-scale model...This article presents a micro-macro unified model for predicting the deformation of metal matrix composites （MMCs）. A macro-scale model is developed to obtain the proper boundary conditions for the micro-scale model, which is used to assess the microstructural deformation of materials. The usage of the submodel technique in the analysis makes it possible to shed light on the stress and strain field at the microlevel. This is helpful to investigate the linkage between the microscopic and the macroscopic flow behavior of the composites. An iterative procedure is also proposed to find out the optimum parameters. The results show that the convergence can be attained after three iterations in computation. In order to demonstrate the reliability of mi- cro-macro unified model, results based on the continuum composite model are also investigated using the stress-strain relation of composite obtained from the iterations. By comparing the proposed unified model to the continuum composite model, it is clear that the former exhibits large plastic deformation in the case of little macroscopic deformation, and the stresses and strains obtained from the submodel are higher than those from the macroscopic deformation.展开更多
We theoretically study complementarity between micro-micro and micro-macro entanglement in a Bose–Einstein condensate with two Rydberg impurities.We investigate quantum dynamics of micro-micro and micro-macro entangl...We theoretically study complementarity between micro-micro and micro-macro entanglement in a Bose–Einstein condensate with two Rydberg impurities.We investigate quantum dynamics of micro-micro and micro-macro entanglement in the micro-macro system.It is found that strong micro-macro entanglement between Rydberg impurities and the BEC can be generated by the use of initial micro-micro entanglement between two Rydberg impurities,which acts as the seed entanglement to create micro-macro entanglement.We demonstrate a curious complementarity relation between micro-micro and micro-macro entanglement,and find that the complementarity property can be sustained to some extent even though in the presence of the BEC decoherence.展开更多
MXene,as a rising star among two-dimensional(2D)electromagnetic wave materials,faces urgent challenges in addressing its self-stacking issue and regulating its conductivity.Herein,a micro-macro collaborative design st...MXene,as a rising star among two-dimensional(2D)electromagnetic wave materials,faces urgent challenges in addressing its self-stacking issue and regulating its conductivity.Herein,a micro-macro collaborative design strategy was proposed to regulate heterogeneous interface engineering in MXene-based absorbers.Biomass-based cotton was introduced as three dimensional(3D)framework for constructing a porous structure,TiO_(2) was in-situ generated and nitrogen atom was doped on Ti_(3)C_(2)T_(x) MXene to regulate its dielectric properties,a 3D N-doped carbon fiber/MXene/TiO_(2)(CMT)nano-aerogel was successful constructed.The synergistic effects of diverse components and structural designs,porous frameworks and TiO_(2) lattice contraction can significantly adjust the density of the conductive network and create abundant heterogeneous interfaces,as well as the lattice defects induced by nitrogen atom doping can enhance polarization loss,ultimately leading to the excellent microwave absorption performance of 3D N-CMT nano-aerogels.The optimized N-CMT 30%aerogel exhibited a minimum reflection loss(RLmin)of−72.56 dB and an effective absorption bandwidth(EAB)of 6.92 GHz at 2.23 mm.Notably,when the thickness was adjusted from 1 to 5 mm,the EAB of the N-CMT 30%aerogel reached 13.94 GHz,achieving coverage of 98% of the C-band and the entire X and Ku bands.Furthermore,the attenuation capabilities of the N-CMT aerogel were further confirmed through RCS simulations,whose RCS reduction value reaches up to 19.969 dB·m^(2).These results demonstrate that 3D N-CMT nano-aerogel relying on interface engineering design exhibits significant potential in the field of electromagnetic protection,providing an important reference for future efficient absorbers.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.51708016,52438007 and 12172036)the R&D program of Beijing Municipal Education Commission(Grant No.KM202110016014)+1 种基金the Pyramid Talent Training Project of Beijing University of Civil Engineering and Architecture(Grant No.JDYC20200307)the Graduate Innovation Program of Beijing University of Civil Engineering and Architecture(Grant No.PG2025060).
文摘The fatigue fracture under cyclic dynamic direct tensions of brittle rock is an important mechanical characteristic index for the evaluation of geological disasters and underground engineering safety.However,most studies focus on macroscopic fracture mechanical properties,and the mechanism linking the macroscopic fracture with the microcrack growth during the cyclic dynamic direct tensile loading of brittle rocks is rarely studied.In this paper,a micro-macro fracture model explaining the stress-strain constitutive relationship is established at the last impact failure after being subjected to multiple cyclic direct tensile impacts of brittle rocks.This model is based on the wing crack extension model under direct tensile loading,the quasi-static and dynamic fracture toughness relationship,the suggested crack rate and strain rate relationship,the relationship of damage and dynamic tensile fatigue life N,the relationship of dynamic fracture toughness and dynamic tensile fatigue life N.The variations of dynamic mechanical properties of rocks with dynamic tensile fatigue life for different initial crack sizes and angles within the rocks are further discussed.The compressive strength,elastic modulus,crack initiation stress,limit crack extension length and crack extension rate descend and the failure strain ascends with an increment of dynamic tensile fatigue life in rocks.This study's results provide help for the safety and stability of the underground surrounding rocks under blasting working or seismic disasters.
基金Aeronautical Basic Science Foundation of China (03H53048)
文摘This article presents a micro-macro unified model for predicting the deformation of metal matrix composites （MMCs）. A macro-scale model is developed to obtain the proper boundary conditions for the micro-scale model, which is used to assess the microstructural deformation of materials. The usage of the submodel technique in the analysis makes it possible to shed light on the stress and strain field at the microlevel. This is helpful to investigate the linkage between the microscopic and the macroscopic flow behavior of the composites. An iterative procedure is also proposed to find out the optimum parameters. The results show that the convergence can be attained after three iterations in computation. In order to demonstrate the reliability of mi- cro-macro unified model, results based on the continuum composite model are also investigated using the stress-strain relation of composite obtained from the iterations. By comparing the proposed unified model to the continuum composite model, it is clear that the former exhibits large plastic deformation in the case of little macroscopic deformation, and the stresses and strains obtained from the submodel are higher than those from the macroscopic deformation.
基金supported by the National Natural Science Foundation of China under Grants Nos 11775075,11434011,and 11935006.
文摘We theoretically study complementarity between micro-micro and micro-macro entanglement in a Bose–Einstein condensate with two Rydberg impurities.We investigate quantum dynamics of micro-micro and micro-macro entanglement in the micro-macro system.It is found that strong micro-macro entanglement between Rydberg impurities and the BEC can be generated by the use of initial micro-micro entanglement between two Rydberg impurities,which acts as the seed entanglement to create micro-macro entanglement.We demonstrate a curious complementarity relation between micro-micro and micro-macro entanglement,and find that the complementarity property can be sustained to some extent even though in the presence of the BEC decoherence.
基金supported by National Natural Science Foundation of China(61374055)Natural Science Foundation of Jiangsu Province(BK20131381)+3 种基金China Postdoctoral Science Foundation funded project(2013M541663)Jiangsu Planned Projects for Postdoctoral Research Funds(1202015C)Scientific Research Foundation for the Returned Overseas Chinese Scholars,State Education Ministry(BJ213022)Scientific Research Foundation of Nanjing University of Posts and Telecommunications(NY214075,XJKY14004)
基金This work was supported by Joint Funds of the National Natural Science Foundation of China(Nos.U22A20244,U23A20673 and 52478261)Qingchuang Technology Project under Grant 2021KJ045,Demonstration Project of Benefiting People with Science and Technology of Qingdao,China(No.24-1-8-cspz-9 nsh)the China Postdoctoral Science Foundation(No.2024M750580).
文摘MXene,as a rising star among two-dimensional(2D)electromagnetic wave materials,faces urgent challenges in addressing its self-stacking issue and regulating its conductivity.Herein,a micro-macro collaborative design strategy was proposed to regulate heterogeneous interface engineering in MXene-based absorbers.Biomass-based cotton was introduced as three dimensional(3D)framework for constructing a porous structure,TiO_(2) was in-situ generated and nitrogen atom was doped on Ti_(3)C_(2)T_(x) MXene to regulate its dielectric properties,a 3D N-doped carbon fiber/MXene/TiO_(2)(CMT)nano-aerogel was successful constructed.The synergistic effects of diverse components and structural designs,porous frameworks and TiO_(2) lattice contraction can significantly adjust the density of the conductive network and create abundant heterogeneous interfaces,as well as the lattice defects induced by nitrogen atom doping can enhance polarization loss,ultimately leading to the excellent microwave absorption performance of 3D N-CMT nano-aerogels.The optimized N-CMT 30%aerogel exhibited a minimum reflection loss(RLmin)of−72.56 dB and an effective absorption bandwidth(EAB)of 6.92 GHz at 2.23 mm.Notably,when the thickness was adjusted from 1 to 5 mm,the EAB of the N-CMT 30%aerogel reached 13.94 GHz,achieving coverage of 98% of the C-band and the entire X and Ku bands.Furthermore,the attenuation capabilities of the N-CMT aerogel were further confirmed through RCS simulations,whose RCS reduction value reaches up to 19.969 dB·m^(2).These results demonstrate that 3D N-CMT nano-aerogel relying on interface engineering design exhibits significant potential in the field of electromagnetic protection,providing an important reference for future efficient absorbers.
