The effects of the addition of rare earth （RE） elements on the void band in the diffusion layer, and the re sistances to both oxidation and spalling of aluminized steel were investigated through high temperature oxi...The effects of the addition of rare earth （RE） elements on the void band in the diffusion layer, and the re sistances to both oxidation and spalling of aluminized steel were investigated through high temperature oxidation and spalling tests. The results showed that RE had significant effects on the void band in the diffusion layer and the properties of aluminized steel. After diffusion treatment, a considerable number of the voids between the middle layer and transitional layer of pure aluminized coating, aggregated into wavy-line-shaped void bands parallel to the outer surface. For the RE added aluminized coating, only a few voids aggregated into intermittent block shapes. During high temperature oxidation at 800 ℃ for 200 h, the wavy void band of pure aluminized coating aggregated further into a linear crack parallel to the outer surface, and the internal oxidation occurred within them; the open cracks perpendicular to the surface penetrated through the diffusion layer. For the RE added aluminized coating, only a few voids aggregated into intermittent meniscus shapes. During cyclic spalling tests, the peeling, spallation, and pulver ulent cracking occurred along the void band in the diffusion layer of pure aluminized coating, but only a little spallation occurred in the diffusion layer of the RE-added aluminized coating, in which cracks perpendicular to the surface were much smaller than those of pure aluminized coating and did not penetrate through the diffusion layer. It is evident that RE addition can restrain the formation and aggregation of voids and subsequently improve the resistances to oxidation and spalling. The mechanism of the RE effect on the void band in the diffusion layer is also discussed.展开更多
An explanation of the meso-mechanism of sand granular materials for the uniqueness of critical state is presented by means of the discrete element method(DEM)under flexible boundary loading conditions.A series triaxia...An explanation of the meso-mechanism of sand granular materials for the uniqueness of critical state is presented by means of the discrete element method(DEM)under flexible boundary loading conditions.A series triaxial drainage shear test(DEM simulations),in conjunction with the flexible boundary technique,of were performed for sand samples subjected to various physical states and with different particle size distributions.After carefully investigating the critical status of the results of the numerical calculation,the macroscopic failure modes and shear band evolution of sand,as well as the velocity vector field due to different initial states,were explored and classified.Furthermore,the evaluation rules and discrepancies between overall void ratios of the specimen and local void ratios within the shear band under the critical state were recorded and analyzed.The results proved that a sample with a small void tends to form a shear band,and the rotation of the particles in the non-shear zone is negligible.Conversely,sandy soil with large initial void ratios exhibited limited development of significant shear bands,and the change in void ratios within the shear region and the non-shear area are not significant.Interestingly,the particle-size distribution exerts minimal influence on the evolution rule which the void ratio converges within the shear band and diverges outside the shear region for both multi-stage and single-stage specimens.The void ratio within the shear band and deviator stress ratio tend to exhibit consistently for the same specimen with different initial physical states,thereby distinguishing the critical state.There is a significantly higher change in void ratio within the shear band compared to outside of it,yet it remains stable within a relatively similar range.Additionally,the invariant of the fabric tensor used to describe the critical state characteristics also demonstrates a high degree of consistency within the shear band.These findings strongly indicate that the critical state exists with展开更多
基金Item Sponsored by Key Science and Technology Plan Foundation of Henan of China (0423023500) and Natural ScienceFoundation of Henan Province (0511021600)
文摘The effects of the addition of rare earth （RE） elements on the void band in the diffusion layer, and the re sistances to both oxidation and spalling of aluminized steel were investigated through high temperature oxidation and spalling tests. The results showed that RE had significant effects on the void band in the diffusion layer and the properties of aluminized steel. After diffusion treatment, a considerable number of the voids between the middle layer and transitional layer of pure aluminized coating, aggregated into wavy-line-shaped void bands parallel to the outer surface. For the RE added aluminized coating, only a few voids aggregated into intermittent block shapes. During high temperature oxidation at 800 ℃ for 200 h, the wavy void band of pure aluminized coating aggregated further into a linear crack parallel to the outer surface, and the internal oxidation occurred within them; the open cracks perpendicular to the surface penetrated through the diffusion layer. For the RE added aluminized coating, only a few voids aggregated into intermittent meniscus shapes. During cyclic spalling tests, the peeling, spallation, and pulver ulent cracking occurred along the void band in the diffusion layer of pure aluminized coating, but only a little spallation occurred in the diffusion layer of the RE-added aluminized coating, in which cracks perpendicular to the surface were much smaller than those of pure aluminized coating and did not penetrate through the diffusion layer. It is evident that RE addition can restrain the formation and aggregation of voids and subsequently improve the resistances to oxidation and spalling. The mechanism of the RE effect on the void band in the diffusion layer is also discussed.
基金supported by the National Natural Science Foundation of China (general program) (grant Nos.52178361,42407214)the National Outstanding Youth Science Fund Project of the National Natural Science Foundation of China (grant No.51722801).
文摘An explanation of the meso-mechanism of sand granular materials for the uniqueness of critical state is presented by means of the discrete element method(DEM)under flexible boundary loading conditions.A series triaxial drainage shear test(DEM simulations),in conjunction with the flexible boundary technique,of were performed for sand samples subjected to various physical states and with different particle size distributions.After carefully investigating the critical status of the results of the numerical calculation,the macroscopic failure modes and shear band evolution of sand,as well as the velocity vector field due to different initial states,were explored and classified.Furthermore,the evaluation rules and discrepancies between overall void ratios of the specimen and local void ratios within the shear band under the critical state were recorded and analyzed.The results proved that a sample with a small void tends to form a shear band,and the rotation of the particles in the non-shear zone is negligible.Conversely,sandy soil with large initial void ratios exhibited limited development of significant shear bands,and the change in void ratios within the shear region and the non-shear area are not significant.Interestingly,the particle-size distribution exerts minimal influence on the evolution rule which the void ratio converges within the shear band and diverges outside the shear region for both multi-stage and single-stage specimens.The void ratio within the shear band and deviator stress ratio tend to exhibit consistently for the same specimen with different initial physical states,thereby distinguishing the critical state.There is a significantly higher change in void ratio within the shear band compared to outside of it,yet it remains stable within a relatively similar range.Additionally,the invariant of the fabric tensor used to describe the critical state characteristics also demonstrates a high degree of consistency within the shear band.These findings strongly indicate that the critical state exists with
