Tailoring grain size can improve the strength of polycrystals by regulating the proportion of grains to grain boundaries and the interaction area.As the grain size decreases to the nanoscale,the deformation mechanism ...Tailoring grain size can improve the strength of polycrystals by regulating the proportion of grains to grain boundaries and the interaction area.As the grain size decreases to the nanoscale,the deformation mechanism in polycrystals shifts from being primarily mediated by dislocations to deformation occurring within the grains and grain boundaries.However,the mechanism responsible for fine-grain strengthening in ferroelectric materials remains unclear,primarily due to the complex multi-field coupling effect arising from spontaneous polarization.Through molecular dynamics simulations,we investigate the strengthening mechanism of barium titanate(BaTiO3),with extremely fine-grain sizes.This material exhibits an inverse Hall–Petch relationship between grain size and strength,rooting in the inhomogeneous concentration of atomic strain and grain rotation.Furthermore,we present a theoretical model to predict the transition from the inverse Hall–Petch stage to the Hall–Petch stage based on strength variations with size,which aligns well with the simulation results.It has been found that the piezoelectric properties of the BaTiO3 are affected by polarization domain switching at various grain sizes.This study enhances our understanding of the atomic-scale mechanisms that contribute to the performance evolution of fine-grain nano-ferroelectric materials.It also provides valuable insights into the design of extremely small-scale ferroelectric components.展开更多
Under environment with various water contents,the variations in the mixing state and particle size of coated black carbon(BC)aerosols cause changes in optical and radiative effects.In this study,fractal models for thi...Under environment with various water contents,the variations in the mixing state and particle size of coated black carbon(BC)aerosols cause changes in optical and radiative effects.In this study,fractal models for thinly,partially,and thickly coated BC under six relative humidities(RHs=0–95%)are constructed and optically simulated at 1064 and 532 nm.Differential scattering cross-sections are selected to retrieve the mixing state(D_(p)/D_(c))of BC to investigate the possible retrieval errors caused by the nonspherical morphology when using the single-particle soot photometer(SP2).Furthermore,the radiative forcing of BC aerosols at different RHs are analyzed.Results showed that the retrieval errors(REs)of D_(p)/D_(c) are negative for coated particles with BC volume fraction smaller than 0.10,indicating that the mixing states of coated fractal BC are underestimated during the hygroscopic growth.The partially-coated BC has the best retrieval accuracy of the mixing state,followed by the closed-cell and coated-aggregate model,judging from averaged REs.Radiative forcing enhancements for partially-coated aerosols with different BC volume fractions exponentially increase to opposite values,resulting in a warming or cooling effect.This study helps understand the uncertainties in Dp/Dc of BC aerosols retrieved by SP2 and their radiative forcing at different RHs.展开更多
A design strategy for a mechanical metamaterial with large negative hygroscopic expansion(NHE)was proposed in this paper.Different from the reported structures,the present metamaterial is designed by constructing repe...A design strategy for a mechanical metamaterial with large negative hygroscopic expansion(NHE)was proposed in this paper.Different from the reported structures,the present metamaterial is designed by constructing repeated lattice microstructure consisting of curved ligaments incorporating hydrogel active layers and polymer support layers and straight polymer bars.When immersed in the solution environment,the swelling of hydrogel layer of such composite structure induces the reversed bending of the ligament,leading to the overall ultra-large shrink(negative expansion)deformation of the metamaterial.Through the new structural design,large NHE effects can be achieved.The theoretical investigation and finite element analysis(FEA)were conducted to demonstrate the large negative expansion effects of such metamaterial.The results showed that the effective NHE ratio of the metamaterial is dependent of the curvature of the curved ligament and the size of both the ligament and the connecting rod.The ultra-large NHE ratios about−80%for the 2D structure and−90%for the 3D version can be obtained by adopting the structural parameters.The newly designed metamaterials have potential applications in medical and other fields.展开更多
基金supported by the National Natural Science Foundation of China(Nos.12172117,12372154)National Science and Technology Major Project(No.J2019-1II-0010-0054)+1 种基金National Numerical Windtunnel(No.NNW2019-JT01-023)High-Performance Computing Center of Hebei University。
文摘Tailoring grain size can improve the strength of polycrystals by regulating the proportion of grains to grain boundaries and the interaction area.As the grain size decreases to the nanoscale,the deformation mechanism in polycrystals shifts from being primarily mediated by dislocations to deformation occurring within the grains and grain boundaries.However,the mechanism responsible for fine-grain strengthening in ferroelectric materials remains unclear,primarily due to the complex multi-field coupling effect arising from spontaneous polarization.Through molecular dynamics simulations,we investigate the strengthening mechanism of barium titanate(BaTiO3),with extremely fine-grain sizes.This material exhibits an inverse Hall–Petch relationship between grain size and strength,rooting in the inhomogeneous concentration of atomic strain and grain rotation.Furthermore,we present a theoretical model to predict the transition from the inverse Hall–Petch stage to the Hall–Petch stage based on strength variations with size,which aligns well with the simulation results.It has been found that the piezoelectric properties of the BaTiO3 are affected by polarization domain switching at various grain sizes.This study enhances our understanding of the atomic-scale mechanisms that contribute to the performance evolution of fine-grain nano-ferroelectric materials.It also provides valuable insights into the design of extremely small-scale ferroelectric components.
基金This research was supported by the National Natural Science Foundation of China(grant No.42305082)the Hebei Natural Science Foundation(grant No.D2024201001)+3 种基金the Science Research Project of the Hebei Education Department(grant No.BJK2024179)the China Postdoctoral Science Foundation(grant No.2024M750493)the Innovation Team of Nondestructive Testing Technology and Instrument,Hebei University(grant No.IT2023C03)the Interdisciplinary Research Program of Natural Science of Hebei University(grant No.DXK201915).
文摘Under environment with various water contents,the variations in the mixing state and particle size of coated black carbon(BC)aerosols cause changes in optical and radiative effects.In this study,fractal models for thinly,partially,and thickly coated BC under six relative humidities(RHs=0–95%)are constructed and optically simulated at 1064 and 532 nm.Differential scattering cross-sections are selected to retrieve the mixing state(D_(p)/D_(c))of BC to investigate the possible retrieval errors caused by the nonspherical morphology when using the single-particle soot photometer(SP2).Furthermore,the radiative forcing of BC aerosols at different RHs are analyzed.Results showed that the retrieval errors(REs)of D_(p)/D_(c) are negative for coated particles with BC volume fraction smaller than 0.10,indicating that the mixing states of coated fractal BC are underestimated during the hygroscopic growth.The partially-coated BC has the best retrieval accuracy of the mixing state,followed by the closed-cell and coated-aggregate model,judging from averaged REs.Radiative forcing enhancements for partially-coated aerosols with different BC volume fractions exponentially increase to opposite values,resulting in a warming or cooling effect.This study helps understand the uncertainties in Dp/Dc of BC aerosols retrieved by SP2 and their radiative forcing at different RHs.
基金supported by the National Natural Science Foundation of China[12172117]Science Foundation for Returned Scholars of Hebei Province of China[C20190318]。
文摘A design strategy for a mechanical metamaterial with large negative hygroscopic expansion(NHE)was proposed in this paper.Different from the reported structures,the present metamaterial is designed by constructing repeated lattice microstructure consisting of curved ligaments incorporating hydrogel active layers and polymer support layers and straight polymer bars.When immersed in the solution environment,the swelling of hydrogel layer of such composite structure induces the reversed bending of the ligament,leading to the overall ultra-large shrink(negative expansion)deformation of the metamaterial.Through the new structural design,large NHE effects can be achieved.The theoretical investigation and finite element analysis(FEA)were conducted to demonstrate the large negative expansion effects of such metamaterial.The results showed that the effective NHE ratio of the metamaterial is dependent of the curvature of the curved ligament and the size of both the ligament and the connecting rod.The ultra-large NHE ratios about−80%for the 2D structure and−90%for the 3D version can be obtained by adopting the structural parameters.The newly designed metamaterials have potential applications in medical and other fields.
