Short carbon fibers were treated at high temperatures around 1100℃ through chemical vapor infiltration technology. A thinner layer ofpyrocarbon was deposited on the fiber surface. The dispersion of carbon fibers in a...Short carbon fibers were treated at high temperatures around 1100℃ through chemical vapor infiltration technology. A thinner layer ofpyrocarbon was deposited on the fiber surface. The dispersion of carbon fibers in a cement matrix and the mechanical properties of carbon fiber/cement composites were investigated by scanning electron microscopy （SEM） and other tests. The reflec- tivity of electromagnetic waves by the composites was measured in the frequency range of 8.0-18 GHz for different carbon fiber contents of 0.2wt%, 0.4wt%, 0.6wt%, and 1.0wt%. The results show that the reflectivity tends to increase with the increase of fiber content above 0.4wt%. The minimum reflectivity is -19.3 dB and the composites exhibit wave-absorbing performances. After pyrocarbon is deposited on the fiber, all the refiectivity data are far greater. They are all above -10 dB and display mainly wave-reflecting performances.展开更多
The excellent performance of laser-induced removal has been widely recognized,yet the limitation of its applications has been gradually approached for complex multilayer coatings in practical situations.Therefore,it i...The excellent performance of laser-induced removal has been widely recognized,yet the limitation of its applications has been gradually approached for complex multilayer coatings in practical situations.Therefore,it is necessary to clarify the laser-induced removal mechanisms of different material layers,which may contribute to guiding precise and controllable layer-by-layer removal and subsequent repair.Herein,the laser-induced layer-by-layer removal of FeCo-based multilayer wave-absorbing coatings was designed and verified.The macro/micro morphologies and elemental analysis indicated that the removal of the topcoat and wave-absorbing layer was dominated by thermal ablation.Interestingly,experiments and simulations demonstrated that a shift in the removal mechanism,i.e.,from the ablation mechanism to the stripping mechanism,occurred when the laser irradiated the primer.It is mainly attributed to the competing contributions of temperature rise and thermal stress to the removal effect.Subsequent macrodynamic behavior captured by a high-speed camera also validated the combination of both re-moval mechanisms.Additionally,the evolution of the crystalline phase and element valence state was revealed.Further laser-induced breakdown spectroscopy revealed the microscopic material motions dur-ing the layer-by-layer removal,including molecular bond breaking induced by multiphoton absorption,atomic ionization,excitation and compounding of electrons and ions,crystal lattice deformation caused by electron-phonon coupling,etc.Based on the above analysis,the thermo-mechanical action mechanisms and microscopic motion models of laser-induced layer-by-layer removal for FeCo-based multilayer wave-absorbing coatings were established,which is expected to be an ideal method for breaking through the limitation of laser-induced removal’s applications.展开更多
MnO_2/activated carbon composite（Mn-ACC） wave absorber was prepared by the reaction between Mn（CH_3COO）_2 and KMnO_4 on activated carbon. Then, a novel cement based composite absorbing coating（CB-CAC） was prepar...MnO_2/activated carbon composite（Mn-ACC） wave absorber was prepared by the reaction between Mn（CH_3COO）_2 and KMnO_4 on activated carbon. Then, a novel cement based composite absorbing coating（CB-CAC） was prepared by adding the Mn-ACC, manganese zinc ferrite and rubber particles into cement. XRD method was used to analyze the reaction products of the Mn-ACC. The tensile bond strength and the wave absorbing properties of the CB-CACs were also tested. The results showed that the crystallinity of MnO_2 formed in the Mn-ACC was poor. Adding Mn-ACC into the CB-CAC led to first increase and then decrease of the tensile bond strength. The tensile bond strength reached 1.89 MPa with 8.51% of the Mn-ACC. The CB-CACs obtained the optimal absorbing properties with the cement, manganese zinc ferrite, Mn-ACC, rubber particles and H_2O mass ratio of 7.5？7.5？1？1？5.5, respectively. The band width of the reflection below-10 dB was up to 8.8 GHz, which accounted for 57.14% of the test band.展开更多
Improving the atom utilization of metals and clarifying the M–M’interaction is both greatly significant in assembling high-performance ultra-light electromagnetic wave-absorbing materials.Herein,a high-temperature e...Improving the atom utilization of metals and clarifying the M–M’interaction is both greatly significant in assembling high-performance ultra-light electromagnetic wave-absorbing materials.Herein,a high-temperature explosion strategy has been successfully applied to assemble the hierarchical porous carbon sponge with Co–Fe decoration via the pyrolysis of the energetic metal organic framework.The as-constructed hybrid displays a superior reflection loss(RL)value of-57.7 d B and a specific RL value of-192 d B mg-1 mm-1 at 12.08 GHz with a layer thickness of 2.0 mm(loading of 15 wt%).The off-axis electron hologram characterizes the highly distributed numerous polarized nanodomain variable capacitors,demonstrating the dipole and interfacial polarization along the edges of the nanopores.More importantly,the X-ray absorption spectroscopy analysis verifies the mutual interaction between the metal cluster and carbon matrix and the electronic coupling responsible for the greatly improved electromagnetic wave absorption.展开更多
In this work, Green-Naghdi （GN） equations with general weight functions were derived in a simple way. A wave-absorbing beach was also considered in the general GN equations. A numerical solution for a level higher t...In this work, Green-Naghdi （GN） equations with general weight functions were derived in a simple way. A wave-absorbing beach was also considered in the general GN equations. A numerical solution for a level higher than 4 was not feasible in the past with the original GN equations. The GN equations for shallow water waves were simplified here, which make the application of high level （higher than 4） equations feasible. The linear dispersion relationships of the first seven levels were presented. The accuracy of dispersion relationships increased as the level increased. Level 7 GN equations are capable of simulating waves out to wave number times depth kd 〈 26. Numerical simulation of nonlinear water waves was performed by use of Level 5 and 7 GN equations, which will be presented in the next paper.展开更多
Time-delayed rockbursts abruptly release huge energy,characterized by suddenness,randomness,and destructiveness,leading to substantial damage to both lives and property.This study explores the occurrence of time-delay...Time-delayed rockbursts abruptly release huge energy,characterized by suddenness,randomness,and destructiveness,leading to substantial damage to both lives and property.This study explores the occurrence of time-delayed rockbursts through statistical analysis of case studies in deep tunnels,including an extremely intensive time-delayed rockburst case.Through on-site surveys,blasting vibration tests,numerical calculations,and true triaxial compression experiments,this study analyzes the main factors and prevention and control strategies of time-delayed rockbursts based on an extremely intense time-delayed rockburst case.The results show that most time-delayed rockbursts are of high intensity.Paramount factors influencing their occurrence consider in-situ stresses,structural planes,and dynamic disturbances.Both high in-situ stress and its gradients provide the necessary conditions for such events,while the presence of abundant structural planes and frequent dynamic disturbances largely increase the risk of rockburst potential.To mitigate the risk of time-delayed rockbursts,energy control strategies are essential,incorporating measures such as energy reduction,prerelease,energy transformation,and energy absorption.Additionally,wave-absorbed support technology can reduce the amplitude and frequency of dynamic disturbances,further decreasing the likelihood of a rockburst occurring.Time-delayed rockburst occurrence requires long disturbance durations,compared to immediate rockbursts.Long-term,continuous,and multiple dynamic events will cause significant damage accumulation and formation of microcracks in hard rock.This study offers insights into the mechanisms underpinning time-delayed rockbursts and proposes prevention strategies for their control.展开更多
Structure modulation at multiscale is crucialfor optimizing the electromagnetic wave absorption (EWA)properties of fiber-reinforced composites. Here we selectedtwo types of wave-absorbing SiC fibers as reinforcements....Structure modulation at multiscale is crucialfor optimizing the electromagnetic wave absorption (EWA)properties of fiber-reinforced composites. Here we selectedtwo types of wave-absorbing SiC fibers as reinforcements. TheL-fiber had a relatively low resistivity of ~3 Ω·cm and the Hfiberhad a high resistivity of ~7×10^(5)Ω·cm. To adjust the impedance,BN single coating and SiO_(2)/BN dual-coating wereprepared respectively on the L-fibers. Unidirectional prepregswith different fibers were stacked in different rules to obtainthe final composites. It showed that both the fiber coatings andstacking structure significantly influence the EWA performanceof the composites. Guided by computational optimization,the stacked composites exhibited superior reflectionloss (RL) lower than −10 dB across the whole X(8.2–12.4 GHz) and Ku (12.4–18.0 GHz) bands. It is interestingto find that the introduction of the surface coatings on theL-fibers significantly widens the available thickness range ofthe stacked composite for possessing excellent performance. Inparticular, dual-coating perform better in terms of broadeningthe available thickness range of the stacked composites.展开更多
基金supported by the National Natural Science Foundation of China (No.50172039)
文摘Short carbon fibers were treated at high temperatures around 1100℃ through chemical vapor infiltration technology. A thinner layer ofpyrocarbon was deposited on the fiber surface. The dispersion of carbon fibers in a cement matrix and the mechanical properties of carbon fiber/cement composites were investigated by scanning electron microscopy （SEM） and other tests. The reflec- tivity of electromagnetic waves by the composites was measured in the frequency range of 8.0-18 GHz for different carbon fiber contents of 0.2wt%, 0.4wt%, 0.6wt%, and 1.0wt%. The results show that the reflectivity tends to increase with the increase of fiber content above 0.4wt%. The minimum reflectivity is -19.3 dB and the composites exhibit wave-absorbing performances. After pyrocarbon is deposited on the fiber, all the refiectivity data are far greater. They are all above -10 dB and display mainly wave-reflecting performances.
基金support from the National Natural Science Foundation of China(Nos.52075246 and U2341264)the Natural Science Foundation of Jiangsu Province(Nos.BK20211568 and BZ2023045)+2 种基金National Science and Technology Major Project of China(No.J2019-Ⅲ-0010-0054)Fundamental Research Funds for the Central Universities(No.NE2022005)Liaoning Provincial Key Laboratory of Aircraft Ice Protection(No.XFX20220301).
文摘The excellent performance of laser-induced removal has been widely recognized,yet the limitation of its applications has been gradually approached for complex multilayer coatings in practical situations.Therefore,it is necessary to clarify the laser-induced removal mechanisms of different material layers,which may contribute to guiding precise and controllable layer-by-layer removal and subsequent repair.Herein,the laser-induced layer-by-layer removal of FeCo-based multilayer wave-absorbing coatings was designed and verified.The macro/micro morphologies and elemental analysis indicated that the removal of the topcoat and wave-absorbing layer was dominated by thermal ablation.Interestingly,experiments and simulations demonstrated that a shift in the removal mechanism,i.e.,from the ablation mechanism to the stripping mechanism,occurred when the laser irradiated the primer.It is mainly attributed to the competing contributions of temperature rise and thermal stress to the removal effect.Subsequent macrodynamic behavior captured by a high-speed camera also validated the combination of both re-moval mechanisms.Additionally,the evolution of the crystalline phase and element valence state was revealed.Further laser-induced breakdown spectroscopy revealed the microscopic material motions dur-ing the layer-by-layer removal,including molecular bond breaking induced by multiphoton absorption,atomic ionization,excitation and compounding of electrons and ions,crystal lattice deformation caused by electron-phonon coupling,etc.Based on the above analysis,the thermo-mechanical action mechanisms and microscopic motion models of laser-induced layer-by-layer removal for FeCo-based multilayer wave-absorbing coatings were established,which is expected to be an ideal method for breaking through the limitation of laser-induced removal’s applications.
基金Funded by the International Cooperation Office of the Ministry of Science and Technology of China(2013DFR50360)the Postdoctoral Research Foundation of Shenyang Ligong University,the Open Fund from Advanced Processing Technology of Metal Materials of Liaoning Key Laboratory,Shenyang Ligong Universitythe Guide Project from Liaoning Natural Science Foundation of China(No.201602646)
文摘MnO_2/activated carbon composite（Mn-ACC） wave absorber was prepared by the reaction between Mn（CH_3COO）_2 and KMnO_4 on activated carbon. Then, a novel cement based composite absorbing coating（CB-CAC） was prepared by adding the Mn-ACC, manganese zinc ferrite and rubber particles into cement. XRD method was used to analyze the reaction products of the Mn-ACC. The tensile bond strength and the wave absorbing properties of the CB-CACs were also tested. The results showed that the crystallinity of MnO_2 formed in the Mn-ACC was poor. Adding Mn-ACC into the CB-CAC led to first increase and then decrease of the tensile bond strength. The tensile bond strength reached 1.89 MPa with 8.51% of the Mn-ACC. The CB-CACs obtained the optimal absorbing properties with the cement, manganese zinc ferrite, Mn-ACC, rubber particles and H_2O mass ratio of 7.5？7.5？1？1？5.5, respectively. The band width of the reflection below-10 dB was up to 8.8 GHz, which accounted for 57.14% of the test band.
基金This work was financially supported by the National Natural Science Foundation of China(22001156)the Youth Talent Fund of University Association for Science and Technology in Shaanxi,China(20210602)+1 种基金King Abdullah University of Science and Technology(KAUST)Open access funding provided by Shanghai Jiao Tong University
文摘Improving the atom utilization of metals and clarifying the M–M’interaction is both greatly significant in assembling high-performance ultra-light electromagnetic wave-absorbing materials.Herein,a high-temperature explosion strategy has been successfully applied to assemble the hierarchical porous carbon sponge with Co–Fe decoration via the pyrolysis of the energetic metal organic framework.The as-constructed hybrid displays a superior reflection loss(RL)value of-57.7 d B and a specific RL value of-192 d B mg-1 mm-1 at 12.08 GHz with a layer thickness of 2.0 mm(loading of 15 wt%).The off-axis electron hologram characterizes the highly distributed numerous polarized nanodomain variable capacitors,demonstrating the dipole and interfacial polarization along the edges of the nanopores.More importantly,the X-ray absorption spectroscopy analysis verifies the mutual interaction between the metal cluster and carbon matrix and the electronic coupling responsible for the greatly improved electromagnetic wave absorption.
基金Supported by the Special Fund for Basic Scientific Research of Central Colleges Harbin Engineering University(Harbin)the National Natural Science Foundation of China+1 种基金Doctor Subject Foundation of the Ministry of Education of Chinathe"111"project(B07019)
文摘In this work, Green-Naghdi （GN） equations with general weight functions were derived in a simple way. A wave-absorbing beach was also considered in the general GN equations. A numerical solution for a level higher than 4 was not feasible in the past with the original GN equations. The GN equations for shallow water waves were simplified here, which make the application of high level （higher than 4） equations feasible. The linear dispersion relationships of the first seven levels were presented. The accuracy of dispersion relationships increased as the level increased. Level 7 GN equations are capable of simulating waves out to wave number times depth kd 〈 26. Numerical simulation of nonlinear water waves was performed by use of Level 5 and 7 GN equations, which will be presented in the next paper.
基金supported by the National Natural Science Foundation of China(Grant Nos.52222810 and 52178383).
文摘Time-delayed rockbursts abruptly release huge energy,characterized by suddenness,randomness,and destructiveness,leading to substantial damage to both lives and property.This study explores the occurrence of time-delayed rockbursts through statistical analysis of case studies in deep tunnels,including an extremely intensive time-delayed rockburst case.Through on-site surveys,blasting vibration tests,numerical calculations,and true triaxial compression experiments,this study analyzes the main factors and prevention and control strategies of time-delayed rockbursts based on an extremely intense time-delayed rockburst case.The results show that most time-delayed rockbursts are of high intensity.Paramount factors influencing their occurrence consider in-situ stresses,structural planes,and dynamic disturbances.Both high in-situ stress and its gradients provide the necessary conditions for such events,while the presence of abundant structural planes and frequent dynamic disturbances largely increase the risk of rockburst potential.To mitigate the risk of time-delayed rockbursts,energy control strategies are essential,incorporating measures such as energy reduction,prerelease,energy transformation,and energy absorption.Additionally,wave-absorbed support technology can reduce the amplitude and frequency of dynamic disturbances,further decreasing the likelihood of a rockburst occurring.Time-delayed rockburst occurrence requires long disturbance durations,compared to immediate rockbursts.Long-term,continuous,and multiple dynamic events will cause significant damage accumulation and formation of microcracks in hard rock.This study offers insights into the mechanisms underpinning time-delayed rockbursts and proposes prevention strategies for their control.
基金supported by the Natural Science Foundation of Xiamen, China (3502Z202373011)the Fundamental Research Funds for the Central Universities (20720220066, 20720230027)the National Key Project of China (2022-JCJQ-ZD-067-11)。
文摘Structure modulation at multiscale is crucialfor optimizing the electromagnetic wave absorption (EWA)properties of fiber-reinforced composites. Here we selectedtwo types of wave-absorbing SiC fibers as reinforcements. TheL-fiber had a relatively low resistivity of ~3 Ω·cm and the Hfiberhad a high resistivity of ~7×10^(5)Ω·cm. To adjust the impedance,BN single coating and SiO_(2)/BN dual-coating wereprepared respectively on the L-fibers. Unidirectional prepregswith different fibers were stacked in different rules to obtainthe final composites. It showed that both the fiber coatings andstacking structure significantly influence the EWA performanceof the composites. Guided by computational optimization,the stacked composites exhibited superior reflectionloss (RL) lower than −10 dB across the whole X(8.2–12.4 GHz) and Ku (12.4–18.0 GHz) bands. It is interestingto find that the introduction of the surface coatings on theL-fibers significantly widens the available thickness range ofthe stacked composite for possessing excellent performance. Inparticular, dual-coating perform better in terms of broadeningthe available thickness range of the stacked composites.
