Self-healing hydrogels utilize inherent intermolecular forces to autonomously heal physical damage resulting from excessive strain,pressure,or tearing.Applying these materials in soft robotics and tissue engineering c...Self-healing hydrogels utilize inherent intermolecular forces to autonomously heal physical damage resulting from excessive strain,pressure,or tearing.Applying these materials in soft robotics and tissue engineering could be beneficial.On the other hand,their efficacy in stretchable and mechanically resistant circuits is hindered by their limited electrical conductivity.展开更多
This paper presents an overview of experimental investigations conducted at China University of Mining and Technology Beijing(CUMTB) on roadway excavation using large-scale geomechanical model tests.The simulated sedi...This paper presents an overview of experimental investigations conducted at China University of Mining and Technology Beijing(CUMTB) on roadway excavation using large-scale geomechanical model tests.The simulated sedimentary rocks are composed by alternating layers of sandstone, mudstone and coal seam inclined at varied angles with respect to the horizontal including 0°, 45°, 60°, and 90°. During the excavation, infrared thermography was employed to detect the thermal response of the surrounding rocks under excavation. The obtained raw thermograms were processed using denoising algorithm, data reduction procedure and Fourier analysis. The infrared temperature(IRT) characterizes the overall rock response; the processed thermal images represent the structural behavior, and the Fourier spectrum describes damage development in the frequency domain. Deeper understanding was achieved by the comparative analyses of excavation in differently inclined rock masses using the image features of IRTs, thermal images and Fourier spectra.展开更多
When a fire occurs in an underground shield tunnel,it can result in substantial property damage and cause permanent harm to the tunnel lining structure.This is especially true for large-diameter shield tunnels that ha...When a fire occurs in an underground shield tunnel,it can result in substantial property damage and cause permanent harm to the tunnel lining structure.This is especially true for large-diameter shield tunnels that have numerous segments and joints,and are exposed to specific fire conditions in certain areas.This paper constructs a full-scale shield tunnel fire test platform and conducts a non-uniform fire test using the lining system of a three-ring large-diameter shield tunnel with an inner diameter of 10.5 m.Based on the tests,the tem-perature field distribution,high-temperature bursting,cracking phenomena,and deformation under fire conditions are observed.Fur-thermore,the post-fire damage forms of tunnel lining structures are obtained through the post-fire ultimate loading test,and the corresponding mechanism is explained.The test results illustrate that the radial and circumferential distribution of internal temperature within the tunnel lining,as well as the radial temperature gradient distribution on the inner surface of the lining,have non-uniform dis-tribution characteristics.As a result,the macroscopic phenomena of lining concrete bursting and crack development during the fire test mainly occur near the fire source,where the temperature rise gradient is the highest.In addition,the lining structure has a deformation characteristic of local outward expansion and cannot recover after the fire load is removed.The ultimate form of damage after the fire is dominated by crush damage from the inside out of the lining joints in the fire-exposed area.The above results serve as a foundation for future tunnel fire safety design and evaluation.展开更多
The accumulation of highly adhesive dust on spacecraft presents a serious issue to hinder long-term extravehicular activity and the establishment of a permanent station on lunar surface.In contrast to the immediate ph...The accumulation of highly adhesive dust on spacecraft presents a serious issue to hinder long-term extravehicular activity and the establishment of a permanent station on lunar surface.In contrast to the immediate physical damage caused by hypervelocity(>1.0 km/s)impacts,this adhesion observed at low-velocity(0.01 to 100 m/s)collisions can more unobtrusively and mortally degenerate the performance of equipment.This paper proposes a theoretical model aimed at comprehensively analyzing the dynamics of adhesion and escape phenomena occurring during low-velocity impacts between charged dust particles and spacecrafts enveloped by a plasma sheath.The electrostatic force is modeled using the image multipole method,and contact force is calculated based on the adhesive–elastic–plastic theory.The results reveal that the implementation of a dielectric coating possessing both low permittivity and low interface energy can substantially reduce energy dissipation during collisions.However,the ultimate adhesion on the surface or escape from the sheath for low-velocity charged dust is dominated by the long-range electrostatic interaction rather than short-range contact interaction.Positively charged particles of smaller sizes demonstrate a greater propensity for surface adhesion in comparison to negatively charged particles of larger sizes.Counterintuitively,without additional dust removal techniques,modifying the properties of the dielectric coating does not effectively reduce the accumulation of dust,which can be merely accomplished by decreasing the spacecraft’s potential.The model presented in this study serves as a crucial step toward understanding the mechanism of lunar dust pollution.展开更多
文摘Self-healing hydrogels utilize inherent intermolecular forces to autonomously heal physical damage resulting from excessive strain,pressure,or tearing.Applying these materials in soft robotics and tissue engineering could be beneficial.On the other hand,their efficacy in stretchable and mechanically resistant circuits is hindered by their limited electrical conductivity.
基金provided by the Special Funds for the Major State Basic Research Project(No.2006CB202200)the Innovative Team Development Project of the state Educational Ministry of China(No.IRT0656)
文摘This paper presents an overview of experimental investigations conducted at China University of Mining and Technology Beijing(CUMTB) on roadway excavation using large-scale geomechanical model tests.The simulated sedimentary rocks are composed by alternating layers of sandstone, mudstone and coal seam inclined at varied angles with respect to the horizontal including 0°, 45°, 60°, and 90°. During the excavation, infrared thermography was employed to detect the thermal response of the surrounding rocks under excavation. The obtained raw thermograms were processed using denoising algorithm, data reduction procedure and Fourier analysis. The infrared temperature(IRT) characterizes the overall rock response; the processed thermal images represent the structural behavior, and the Fourier spectrum describes damage development in the frequency domain. Deeper understanding was achieved by the comparative analyses of excavation in differently inclined rock masses using the image features of IRTs, thermal images and Fourier spectra.
基金the financial support from the National Natural Science Foundation of China-Joint Fund Project(Grant No.U1834208).
文摘When a fire occurs in an underground shield tunnel,it can result in substantial property damage and cause permanent harm to the tunnel lining structure.This is especially true for large-diameter shield tunnels that have numerous segments and joints,and are exposed to specific fire conditions in certain areas.This paper constructs a full-scale shield tunnel fire test platform and conducts a non-uniform fire test using the lining system of a three-ring large-diameter shield tunnel with an inner diameter of 10.5 m.Based on the tests,the tem-perature field distribution,high-temperature bursting,cracking phenomena,and deformation under fire conditions are observed.Fur-thermore,the post-fire damage forms of tunnel lining structures are obtained through the post-fire ultimate loading test,and the corresponding mechanism is explained.The test results illustrate that the radial and circumferential distribution of internal temperature within the tunnel lining,as well as the radial temperature gradient distribution on the inner surface of the lining,have non-uniform dis-tribution characteristics.As a result,the macroscopic phenomena of lining concrete bursting and crack development during the fire test mainly occur near the fire source,where the temperature rise gradient is the highest.In addition,the lining structure has a deformation characteristic of local outward expansion and cannot recover after the fire load is removed.The ultimate form of damage after the fire is dominated by crush damage from the inside out of the lining joints in the fire-exposed area.The above results serve as a foundation for future tunnel fire safety design and evaluation.
基金supported by the National Natural Science Foundation of China(grant no.52077005).
文摘The accumulation of highly adhesive dust on spacecraft presents a serious issue to hinder long-term extravehicular activity and the establishment of a permanent station on lunar surface.In contrast to the immediate physical damage caused by hypervelocity(>1.0 km/s)impacts,this adhesion observed at low-velocity(0.01 to 100 m/s)collisions can more unobtrusively and mortally degenerate the performance of equipment.This paper proposes a theoretical model aimed at comprehensively analyzing the dynamics of adhesion and escape phenomena occurring during low-velocity impacts between charged dust particles and spacecrafts enveloped by a plasma sheath.The electrostatic force is modeled using the image multipole method,and contact force is calculated based on the adhesive–elastic–plastic theory.The results reveal that the implementation of a dielectric coating possessing both low permittivity and low interface energy can substantially reduce energy dissipation during collisions.However,the ultimate adhesion on the surface or escape from the sheath for low-velocity charged dust is dominated by the long-range electrostatic interaction rather than short-range contact interaction.Positively charged particles of smaller sizes demonstrate a greater propensity for surface adhesion in comparison to negatively charged particles of larger sizes.Counterintuitively,without additional dust removal techniques,modifying the properties of the dielectric coating does not effectively reduce the accumulation of dust,which can be merely accomplished by decreasing the spacecraft’s potential.The model presented in this study serves as a crucial step toward understanding the mechanism of lunar dust pollution.
