As the main geomaterials for coral reefs oil or gas extraction and underground infrastructure construction,coral reef limestone demonstrates significantly distinct mechanical responses compared to terrigenous rocks.To...As the main geomaterials for coral reefs oil or gas extraction and underground infrastructure construction,coral reef limestone demonstrates significantly distinct mechanical responses compared to terrigenous rocks.To investigate the mechanical behaviour of coral reef limestone under the coupling impact of size and strain rate,the uniaxial compression tests were conducted on reef limestone samples with length-to-diameter(L/D)ratio ranging from 0.5 to 2.0 at strain rate ranging from 10^(−5)·s^(−1)to 10^(−2)·s^(−1).It is revealed that the uniaxial compressive strength(UCS)and residual compressive strength(RCS)of coral reef limestone exhibits a decreasing trend with L/D ratio increasing.The dynamic increase factor(DIF)of UCS is linearly correlated with the logarithm of strain rate,while increasing the L/D ratio further enhances the DIF.The elastic modulus increases with strain rate or L/D ratio increasing,whereas the Poisson’s ratio approximates to a constant value of 0.24.The failure strain increases with strain rate increasing or L/D ratio decreasing,while the increase in L/D ratio will inhibit the enhancing effect of the strain rate.The high porosity and low mineral strength are the primary factors contributing to a high RCS of 16.7%–64.9%of UCS,a lower brittleness index and multiple irregular fracture planes.The failure pattern of coral reef limestone transits from the shear-dominated to the splitting-dominated failure with strain rate increasing or L/D ratio decreasing,which is mainly governed by the constrained zones induced by end friction and the strain rate-dependent crack propagation.Moreover,a predictive formula incorporating coupling effect of size and strain rate for the UCS of reef limestone was established and verified to effectively capture the trend of UCS.展开更多
Silicon‐based anode materials have garnered considerable attention in lithium‐ion batteries(LIBs)due to their exceptionally high theoretical capacity and energy density.However,intrinsic challenges,such as significa...Silicon‐based anode materials have garnered considerable attention in lithium‐ion batteries(LIBs)due to their exceptionally high theoretical capacity and energy density.However,intrinsic challenges,such as significant volumetric expansion and the consequent degradation in cycling stability,severely hinder their practical application.As a result,development of silicon anodes that can effectively mitigate volumetric expansions,enhance cycling durability,and improve rate performance has emerged as a critical research focus.However,due to neglect of“size effects”,the modification strategy of silicon‐based electrodes lacks systematic,scientific,and comprehensive guidance.Herein,this review starts from the“size effect”of silicon‐based materials,and reveals in depth the different failure mechanisms of nano‐silicon(Si NPs)and micro‐silicon(μSi).Furthermore,this review provides targeted classification of modification strategies for Si NPs andμSi,and reviews comprehensively,in detail,and in depth the latest research progress on silicon‐based materials.In addition,the review also comprehensively summarizes the cutting‐edge dynamics of matching silicon‐based electrodes with solid electrolytes to construct high‐energy LIBs.It is hoped that this review can provide comprehensive and systematic scientific guidance for modification strategies of silicon‐based electrodes,which is of great significance for promoting the industrialization process of silicon‐based electrodes in high‐energy LIBs.展开更多
A constitutive model considering the size effect was established to investigate the behavior of CoCrNi medium entropy alloy ultrathin strip in different deformation stages during the uniaxial quasi-static tensile test...A constitutive model considering the size effect was established to investigate the behavior of CoCrNi medium entropy alloy ultrathin strip in different deformation stages during the uniaxial quasi-static tensile test.Results show that when the t/d value is lower than 10.62,the CoCrNi alloy ultrathin strip shows an obvious size-dependent property in the elastic deformation stage.With the decrease in t/d value,the volume fraction of the surface layer grains is increased,leading to the linear decrease in flow stress.In the plastic deformation stage,the material stiffness is correlated with the t/d value.Specifically,as the t/d value increases,the work-hardening capacity of the material is enhanced.When the t/d value increases to 10,the work-hardening capacity reaches a maximum state;when the t/d value is beyond 10,the work-hardening capacity weakens.展开更多
In order to gain a deeper understanding of the effect of pulsed current on the mechanical properties and size effect of nanocrystalline Ni foils,nanocrystalline Ni foils with different grain thickness-to-grain size ra...In order to gain a deeper understanding of the effect of pulsed current on the mechanical properties and size effect of nanocrystalline Ni foils,nanocrystalline Ni foils with different grain thickness-to-grain size ratios(λ)were prepared using pulsed electrodeposition in this paper and unidirectional tensile experiments were carried out at room temperature with different currents and their applied directions.The experimental results show that the nanocrystalline Ni foil produces an obvious electroplasticity effect after applying the current field,and when 300<λ<1100,the current weakens the size effect of nanocrystalline Ni foils to a certain extent,and the angle between the current direction and the deformation direction also affects the mechanical response of nanocrystalline Ni foils,and when the angle between the current direction and the deformation direction is 0°,electroplasticity effect is the best,and the current has the most significant effect of abating the size effect of the material.The mechanism of unidirectional tensile deformation of nanocrystalline Ni foils under the effect of pulsed current was analyzed using TEM and TKD.It was found that the applied pulse current increased the activity of the nanocrystalline boundaries,promoted the movement of dislocations,and reduced the tendency of dislocation entanglement.The higher the peak current density and the smaller the angle between the direction of the current and the direction of deformation,the smaller the grain boundary orientation difference,the more dispersed the grain orientation,and the lower the density of geometrically necessary dislocations(GND)in the deformed nanocrystalline foil,the more significant the effect on material plasticity improvement.展开更多
The development of modern engineering components and equipment features large size,intricate shape and long service life,which places greater demands on valid methods for fatigue performance analysis.Achieving a smoot...The development of modern engineering components and equipment features large size,intricate shape and long service life,which places greater demands on valid methods for fatigue performance analysis.Achieving a smooth transformation between small-scale laboratory specimens’fatigue properties and full-scale engineering components’fatigue strength has been a long-term challenge.In this work,two dominant factors impeding the smooth transformation—notch and size effect were experimentally studied,in which fatigue tests on Al 7075-T6511(a very high-strength aviation alloy)notched specimens of different scales were carried out.Fractography analyses identified the evidence of the size effect on notch fatigue damage evolution.Accordingly,the Energy Field Intensity(EFI)initially developed for multiaxial notch fatigue analysis was improved by utilizing the volume ratio of the Effective Damage Zones(EDZs)for size effect correction.In particular,it was extended to a probabilistic model considering the inherent variability of the fatigue phenomenon.The experimental data of Al 7075-T6511 notched specimens and the model-predicted results were compared,indicating the high potential of the proposed approach in fatigue evaluation under combined notch and size effects.展开更多
Mg-3Gd(wt.%)samples with different initial grain sizes were prepared to evaluate the grain size effect on microstructural evolution during cold rolling and subsequent annealing hardening response.The deformation behav...Mg-3Gd(wt.%)samples with different initial grain sizes were prepared to evaluate the grain size effect on microstructural evolution during cold rolling and subsequent annealing hardening response.The deformation behavior and mechanical response of the as-rolled and annealed samples were systematically investigated by a combination of electron microscopy and microhardness characterization.The results show that the twinning activities were highly suppressed in the fine-grained samples during rolling.Upon increasing the rolling reduction to 40%,ultra-fine grain structures with a volume fraction of∼28%were formed due to the activation of multiple slip systems.Conversely,twinning dominated the early stages of deformation in the coarse-grained samples.After a 10%rolling reduction,numerous twins with a volume fraction of∼23%were formed.Further increasing the rolling reduction to 40%,high-density dislocations were activated and twin structures with a volume fraction of∼36%were formed.The annealing hardening response of deformed samples was effectively enhanced compared to that of the non-deformed samples,which was attributed to the enhanced Gd segregation along grain boundaries,twin boundaries and dislocation cores.Moreover,the grain size and rolling reduction were found to affect the microstructure evolution during annealing,resulting in a notable difference in the annealing hardening response of Mg-3Gd alloy between samples of different grain sizes deformed to different strains.These findings highlight the crucial importance of microstructural and processing parameters in the design of high-strength,cost-effective Mg alloys.展开更多
Ethanol steam reforming(ESR)represents a promising route for sustainable hydrogen production,leveraging the high hydrogen content,renewability,and logistical advantages of ethanol.Although Ni-based catalysts are leadi...Ethanol steam reforming(ESR)represents a promising route for sustainable hydrogen production,leveraging the high hydrogen content,renewability,and logistical advantages of ethanol.Although Ni-based catalysts are leading non-noble candidates for ESR,their practical deployment is hindered by compromised H_(2) production efficiency and rapid deactivation.In this work,we combined catalyst synthesis,kinetic analysis,and mechanistic investigation to elucidate the effectsof Ni particle size(3-9 nm)on ESR performance of Ni/CeO_(2) catalysts.These Ni/CeO_(2) catalysts were prepared via a citric acid-assisted coprecipitation method,and systematically characterized using complementary techniques,including high-resolution transmission electron microscopy(HRTEM),in situ X-ray photoelectron spectroscopy(XPS),hydrogen temperature-programmed reduction(H_(2)-TPR),Raman spectroscopy,O_(2)/CO chemisorption,and temperature-programmed surface reaction(TPSR)analyses.Mechanistic study revealed that ethanol dehydrogenation to acetaldehyde is the rate-determining step,defining the intrinsic activity of Ni sites,whereas C-C bond cleavage governs H_(2) selectivity in ESR.At smaller Ni sizes(e.g.,3.1 nm),larger CeO_(2) surface was exposed,which promoted acetaldehyde condensation to acetone,and consequently reduced H_(2) production efficiency.The Ni/CeO_(2) catalyst with~5 nm of Ni particles afforded the highest H_(2) yield(66.3%)and outstanding stability by balancing dehydrogenation activity,H_(2) selectivity,and coking resistance.Conversely,larger Ni particles(>6 nm)facilitated methanation reaction and catalyst deactivation.This work reconciles prior inconsistencies in the Ni size effects on ESR and provides guidance for the design of efficient and durable Ni-based catalysts for H_(2) production.展开更多
Accurate simulation of ice accretion of supercooled large droplet(SLD)is pivotal for the international airworthiness certification of large aircraft.Its complex dynamics behavior and broad particle size distributions ...Accurate simulation of ice accretion of supercooled large droplet(SLD)is pivotal for the international airworthiness certification of large aircraft.Its complex dynamics behavior and broad particle size distributions pose significant challenges to reliable CFD predictions.A numerical model of multi-particle SLD coupling breaking,bouncing and splashing behaviors is established to explore the relationship between dynamics behavior and particle size.The results show that the peak value of droplet collection efficiencyβdecreases due to splashing.The bounce phenomenon will make the impact limit S_(m)of the water drops decrease.With the increase of the SLD particle size,the water drop bounce point gradually moves toward the trailing edge of the wing.The critical breaking diameter of SLD at an airflow velocity of 50 m/s is approximately 100μm.When the SLD particle size increases,the height of the water droplet shelter zone on the upper edge of the wing gradually decreases,and the velocity in the Y direction decreases first and then increases in the opposite direction,increasing the probability of SLD hitting the wing again.Large particle droplets have a higher effect on the impact limit S_(m)than smaller droplets.Therefore,in the numerical simulation of the SLD operating conditions,it is very important to ensure the proportion of large particle size water droplets.展开更多
The size and shape effect(SSE)of components has become a critical issue for mechanical properties,application reliability,and processing.In this study,the creep rupture life(CRL)of components with different wall thick...The size and shape effect(SSE)of components has become a critical issue for mechanical properties,application reliability,and processing.In this study,the creep rupture life(CRL)of components with different wall thicknesses and positions in a combustion chamber casing simulator made of K439B superalloy was investigated.The intrinsic mechanisms of the SSE were explored from the dendrite structure,volume fraction and size of theγ'phase,and element segregation,etc.It is shown that this casting exhibits a strong SSE of creep rupture life,characterized by a significant difference in the CRL values up to 60%with the variation of wall thickness and position in the casing.In terms of casting technology,the influence of SSE on CRL is actually determined by the cooling rate.The SSE on the creep rupture life originates from the dendrite structure(such as the secondary dendrite arm spacing),volume fraction size of theγ'phase in the dendrite trunk,and elements segregation rate.This work may have implications for the design and application of engineering components with large sizes and complex structures.展开更多
To understand the tensile deformation of electro-deposited Cu with nano-scale twins, a numerical study was carried out based on a conventional theory of mechanism-based strain gradient plasticity （CMSG）. The concept...To understand the tensile deformation of electro-deposited Cu with nano-scale twins, a numerical study was carried out based on a conventional theory of mechanism-based strain gradient plasticity （CMSG）. The concept of twin lamella strengthening zone was used in terms of the cohesive interface model to simulate grain-boundary sliding and separation. The model included a number of material parameters, such as grain size, elastic modulus, plastic strain hardening exponent, initial yield stress, as well as twin lamellar distribution, which may contribute to size effects of twin layers in Cu polycrystalline. The results provide information to understand the mechanical behaviors of Cu with nano-scale growth twins.展开更多
The process and mechanism of the ligand volume controlled Pd（PR3）2 （PR3=PH3, PMe3, and PtBu3） oxidative addition with aryl bromide were investigated, using density functional theory method with the conductor-like ...The process and mechanism of the ligand volume controlled Pd（PR3）2 （PR3=PH3, PMe3, and PtBu3） oxidative addition with aryl bromide were investigated, using density functional theory method with the conductor-like screening model. Association pathway and dissocia-tion pathway were investigated by the comparison of several energies. The cleavage energy of Pd（PR3）2 complex was calculated, as well as the oxidative addition reaction barrier energy of Pd（PR3）n （n=1,2） with aryl bromide in N,N-dimethylformamide solvent. This study proved that the ligands volume possessed a great impact on the mechanism of oxidative addition： less bulky ligand palladium associated with aryl bromide via two donor ligands,but larger bulky ligand palladium coordinated via monoligand.展开更多
Micro radial compression tests were carried out on cylindrical specimens of pure copper polycrystals with different grain sizes. Experimental results indicated that phenomena of decreasing forming force, increasing sc...Micro radial compression tests were carried out on cylindrical specimens of pure copper polycrystals with different grain sizes. Experimental results indicated that phenomena of decreasing forming force, increasing scatter of forming force and more irregular surface topography occurred with the increase of grain size. A modified surface model based on dislocations pile-up in surface layer grains, and a flow stress scattering formulation based on standard deviation and grain size distribution were proposed to analyze size effects on forming force in micro compression. The inhomogeneous deformation of surface layer grains was discussed by the main deformation manner of rotation. A good agreement with the experimental results was achieved.展开更多
To investigate the effects of thickness and grain size on mechanical and deformation properties of C5210 phosphor bronze thin sheets, samples with different grain sizes were obtained through annealing heat treatment a...To investigate the effects of thickness and grain size on mechanical and deformation properties of C5210 phosphor bronze thin sheets, samples with different grain sizes were obtained through annealing heat treatment at different temperatures; and then tensile tests of samples with different thicknesses and grain sizes were conducted at room temperature. The results show that yield strength increases with decreasing thickness from 800 to 50 μm, but work hardening exponent and total elongation decrease, and a modified model was proposed to describe the relation between yield strength and thickness; yield strength decreases as the grain size increases, but work hardening exponent shows an increasing trend, total elongation increases to a peak and then decreases. Fracture morphology of tensile specimens was observed by SEM, which indicates that all tensile specimens are ductile fracture. The dimple intensity increases as the specimen thickness increases but reduces with the specimen grain size increasing.展开更多
Hardness of materials depends significantly on the indentation size and grain/sub-grain size via microindentation and nanoindentation tests of high-purity tungsten with different structures.The grain boundary effect a...Hardness of materials depends significantly on the indentation size and grain/sub-grain size via microindentation and nanoindentation tests of high-purity tungsten with different structures.The grain boundary effect and indentation size effect were explored.The indentation hardness was fitted using the Nix-Gao model by considering the scaling factor.The results show that the scaling factor is barely correlated with the grain/sub-grain size.The interaction between the plastically deformed zone（PDZ） boundary and the grain/sub-grain boundary is believed to be the reason that leads to an increase of the measured hardness at the specific depths.Results also indicate that the area of the PDZ is barely correlated with the grain/sub-grain size,and the indentation hardness starts to stabilize once the PDZ expands to the dimension of an individual grain/sub-grain.展开更多
Aluminum alloy （Al-alloy） thin-walled （D/t ＆gt; 20, diameter D, wall thickness t） bent tubes have attracted increasing applications in many industries with mass quantities and diverse specifications due to satisf...Aluminum alloy （Al-alloy） thin-walled （D/t ＆gt; 20, diameter D, wall thickness t） bent tubes have attracted increasing applications in many industries with mass quantities and diverse specifications due to satisfying high strength to weigh ratio requirements of product manufacturing. However, due to nonlinear nature of bending with coupling effects of multiple factors, the similarity theory seems not applicable and there occurs a challenge for efficient and reliable evaluation of the bending formability of thin-walled tube with various bending specifications. Considering the unequal deformation and three major instabilities, the bending formability of thin-walled Al-alloy tube in changing tube sizes such as D and t are clarified via both the analytical and FE modeling/ simulations. The experiments of rotary draw bending are conducted to validate the theoretical models and further confirm ＇size effect＇ related bending formability. The major results show that （1） The anti-wrinkling capability of tube decreases with the larger D and smaller t, and the effect significance of t is larger than that of D even under rigid supports; （2） The wall thinning increases with the larger D and smaller t, and this tendency becomes much more obvious under rigid supports; （3） The cross-section deformation increases with the larger D and smaller t according to the analytical model obtained intrinsic relationship, while this tendency becomes opposite due to the nonlinear role of mandrel die; （4） The size factor D/t can be used as a nondimensional index to evaluate both the bending formability regarding the wall thinning and cross-section deformation.展开更多
Al-Mg-Si-Sc alloys with different Mg/Si ratio(<1.73 in wt.% vs>1.73 in wt.%) and different grain size(coarse grains vs ultrafine grains) were prepared, which allowed to investigate the grain size-dependent Mg/Si...Al-Mg-Si-Sc alloys with different Mg/Si ratio(<1.73 in wt.% vs>1.73 in wt.%) and different grain size(coarse grains vs ultrafine grains) were prepared, which allowed to investigate the grain size-dependent Mg/Si ratio effect on the microstructural evolution and concomitantly on the hardness and electrical conductivity when subjected to aging at 200℃. In the coarse-grained Al-Mg-Sc-Sc alloys, the β" precipitation within the grain interior and also the precipitation hardening were highly dependent on the Mg/Si ratio,while the electrical conductivity was slightly affected by the Mg/Si ratio. A promoted β" precipitation was found in the case of Si excess(Mg/Si ratio <1.73), much greater than in the case of Mg excess(Mg/Si ratio>1.73). While in the ultrafine-grained Al-Mg-Si-Sc alloys, the electrical conductivity rather than the hardness was more sensitive to the Mg/Si ratio. The alloy with Si excess displayed electrical conductivity much higher than its counterpart with Mg excess. This is rationalized by the grain boundary precipitation promoted by Si, which reduced the solute atoms and precipitates within the grain interior. Age softening was found in the ultrafine-grained alloy with Si excess, but the ultrafine-grained alloy with Mg excess held the hardness almost unchanged during the aging. The hardness-conductivity correlation is comprehensively discussed by considering the coupling effect of Mg/Si ratio and grain size. A strategy to simultaneously increase the hardness/strength and electrical conductivity is proposed for the Al-Mg-SiSc alloys, based on present understanding of the predominant factors on strengthening and conductivity,respectively.展开更多
The influences of I,article size on the mechanical properties of the particulate metal matrix composite;are obviously displayed in the experimental observations. However, the phenomenon can not be predicted directly u...The influences of I,article size on the mechanical properties of the particulate metal matrix composite;are obviously displayed in the experimental observations. However, the phenomenon can not be predicted directly using the conventional elastic-plastic theory. It is because that no length scale parameters are involved in the conventional theory. In the present research, using the strain gradient plasticity theory, a systematic research of the particle size effect in the particulate metal matrix composite is carried out. The roles of many composite factors, such as: the particle size, the Young's modulus of the particle, the particle aspect ratio and volume fraction, as well as the plastic strain hardening exponent of the matrix material, are studied in detail. In order to obtain a general understanding for the composite behavior, two kinds of particle shapes, ellipsoid and cylinder, are considered to check the strength dependence of the smooth or non-smooth particle surface. Finally, the prediction results will be applied to the several experiments about the ceramic particle-reinforced metal-matrix composites. The material length scale parameter is predicted.展开更多
In 2002, six cohorts ofbroodstock bay scallop Argopecten irradians irradians （Ne=1, 2, 10, 30, 50 and control） were randomly chosen from a population of bay scallop to produce offspring. After one year rearing, with...In 2002, six cohorts ofbroodstock bay scallop Argopecten irradians irradians （Ne=1, 2, 10, 30, 50 and control） were randomly chosen from a population of bay scallop to produce offspring. After one year rearing, with the progeny matured, the similar experiment was done to produce the F2 generation. To determine the magnitude of Ne effects, the growth and survival rates in larvae and adult of six F2 groups were compared. Results showed that inbreeding depression existed not only in the Ne=1 group but also in the Ne=2 group. The growth and survival rates of the two groups were significantly lower than those of the other groups （Ne=10, 30, 50, control）, and there were no significant differences among the latter （P〉0.05）. At the same time, the amount of depression in the Ne=1 group was significantly higher than that of the Ne=2 group （P〈0.05）. These results indicated that the low effective population size （Ne）, which increases the possibility of inbreeding, could lead to some harmful effects on the offspring. So it is essential to maintain a high level of Ne in commercial seed production. Fta＇thermore, as the high fecundity of bay scallop might lead to increased inbreeding, selecting broodstock from different growout sites is recommended.展开更多
Understanding the size effect exhibited by the fracture mechanism of anisotropic geomaterials is important for engineering practice. In this study, the anisotropic features of the nominal strength, apparent fracture t...Understanding the size effect exhibited by the fracture mechanism of anisotropic geomaterials is important for engineering practice. In this study, the anisotropic features of the nominal strength, apparent fracture toughness, effective fracture energy and fracture process zone(FPZ) size of geomaterials were first analyzed by systematic size effect fracture experiments. The results showed that the nominal strength and the apparent fracture toughness decreased with increasing bedding plane inclination angle.The larger the specimen size was, the smaller the nominal strength and the larger the apparent fracture toughness was. When the bedding inclination angle increased from 0° to 90°, the effective fracture energy and the effective FPZ size both first decreased and then increased within two complex variation stages that were bounded by the 45° bedding angle. Regardless of the inherent anisotropy of geomaterials,the nominal strength and apparent fracture toughness can be predicted by the energy-based size effect law, which demonstrates that geomaterials have obvious quasi-brittle characteristics. Theoretical analysis indicated that the true fracture toughness and energy dissipation can be calculated by linear elastic fracture mechanics only when the brittleness number is higher than 10;otherwise, size effect tests should be adopted to determine the fracture parameters.展开更多
Numerical method is popular in analysing the blast wave propagation and interaction with structures.However,because of the extremely short duration of blast wave and energy trans-mission between different grids,the nu...Numerical method is popular in analysing the blast wave propagation and interaction with structures.However,because of the extremely short duration of blast wave and energy trans-mission between different grids,the numerical results are sensitive to the finite element mesh size.Previous numerical simulations show that a mesh size acceptable to one blast scenario might not be proper for another case,even though the difference between the two scenarios is very small,indicating a simple numerical mesh size convergence test might not be enough to guarantee accu-rate numerical results.Therefore,both coarse mesh and fine mesh were used in different blast scenarios to investigate the mesh size effect on numerical results of blast wave propagation and interaction with structures.Based on the numerical results and their comparison with field test re-sults and the design charts in TM5-1300,a numerical modification method was proposed to correct the influence of the mesh size on the simulated results.It can be easily used to improve the accu-racy of the numerical results of blast wave propagation and blast loads on structures.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52222110,52401354,and 52301353).
文摘As the main geomaterials for coral reefs oil or gas extraction and underground infrastructure construction,coral reef limestone demonstrates significantly distinct mechanical responses compared to terrigenous rocks.To investigate the mechanical behaviour of coral reef limestone under the coupling impact of size and strain rate,the uniaxial compression tests were conducted on reef limestone samples with length-to-diameter(L/D)ratio ranging from 0.5 to 2.0 at strain rate ranging from 10^(−5)·s^(−1)to 10^(−2)·s^(−1).It is revealed that the uniaxial compressive strength(UCS)and residual compressive strength(RCS)of coral reef limestone exhibits a decreasing trend with L/D ratio increasing.The dynamic increase factor(DIF)of UCS is linearly correlated with the logarithm of strain rate,while increasing the L/D ratio further enhances the DIF.The elastic modulus increases with strain rate or L/D ratio increasing,whereas the Poisson’s ratio approximates to a constant value of 0.24.The failure strain increases with strain rate increasing or L/D ratio decreasing,while the increase in L/D ratio will inhibit the enhancing effect of the strain rate.The high porosity and low mineral strength are the primary factors contributing to a high RCS of 16.7%–64.9%of UCS,a lower brittleness index and multiple irregular fracture planes.The failure pattern of coral reef limestone transits from the shear-dominated to the splitting-dominated failure with strain rate increasing or L/D ratio decreasing,which is mainly governed by the constrained zones induced by end friction and the strain rate-dependent crack propagation.Moreover,a predictive formula incorporating coupling effect of size and strain rate for the UCS of reef limestone was established and verified to effectively capture the trend of UCS.
基金supported by The Key R&D Program of Heilongjiang province(2023ZX04A01)The Key Project of Chongqing Technology Innovation and Application Development(2022TIAD‐DEX0024,2023TIAD‐KPX0007)+2 种基金The National Key R&D Program of China(2021YFC2902905)the Beijing Nova Program,the Chongqing Outstanding Youth Fund(2022NSCQ‐JQX3895)the National Natural Science Foundation of China(22109010).
文摘Silicon‐based anode materials have garnered considerable attention in lithium‐ion batteries(LIBs)due to their exceptionally high theoretical capacity and energy density.However,intrinsic challenges,such as significant volumetric expansion and the consequent degradation in cycling stability,severely hinder their practical application.As a result,development of silicon anodes that can effectively mitigate volumetric expansions,enhance cycling durability,and improve rate performance has emerged as a critical research focus.However,due to neglect of“size effects”,the modification strategy of silicon‐based electrodes lacks systematic,scientific,and comprehensive guidance.Herein,this review starts from the“size effect”of silicon‐based materials,and reveals in depth the different failure mechanisms of nano‐silicon(Si NPs)and micro‐silicon(μSi).Furthermore,this review provides targeted classification of modification strategies for Si NPs andμSi,and reviews comprehensively,in detail,and in depth the latest research progress on silicon‐based materials.In addition,the review also comprehensively summarizes the cutting‐edge dynamics of matching silicon‐based electrodes with solid electrolytes to construct high‐energy LIBs.It is hoped that this review can provide comprehensive and systematic scientific guidance for modification strategies of silicon‐based electrodes,which is of great significance for promoting the industrialization process of silicon‐based electrodes in high‐energy LIBs.
基金National Natural Science Foundation of China(12072220,12225207,12372364)National Key Research and Development Program(2018YFA0707300)+2 种基金Major Program of National Natural Science Foundation of China(U22A20188)Central Guidance on Local Science and Technology Development Fund of Shanxi Province(YDZJSX2021B002)Natural Science Foundation of Shanxi Province(202303021211038)。
文摘A constitutive model considering the size effect was established to investigate the behavior of CoCrNi medium entropy alloy ultrathin strip in different deformation stages during the uniaxial quasi-static tensile test.Results show that when the t/d value is lower than 10.62,the CoCrNi alloy ultrathin strip shows an obvious size-dependent property in the elastic deformation stage.With the decrease in t/d value,the volume fraction of the surface layer grains is increased,leading to the linear decrease in flow stress.In the plastic deformation stage,the material stiffness is correlated with the t/d value.Specifically,as the t/d value increases,the work-hardening capacity of the material is enhanced.When the t/d value increases to 10,the work-hardening capacity reaches a maximum state;when the t/d value is beyond 10,the work-hardening capacity weakens.
基金Project(51975167)supported by the National Natural Science Foundation of China。
文摘In order to gain a deeper understanding of the effect of pulsed current on the mechanical properties and size effect of nanocrystalline Ni foils,nanocrystalline Ni foils with different grain thickness-to-grain size ratios(λ)were prepared using pulsed electrodeposition in this paper and unidirectional tensile experiments were carried out at room temperature with different currents and their applied directions.The experimental results show that the nanocrystalline Ni foil produces an obvious electroplasticity effect after applying the current field,and when 300<λ<1100,the current weakens the size effect of nanocrystalline Ni foils to a certain extent,and the angle between the current direction and the deformation direction also affects the mechanical response of nanocrystalline Ni foils,and when the angle between the current direction and the deformation direction is 0°,electroplasticity effect is the best,and the current has the most significant effect of abating the size effect of the material.The mechanism of unidirectional tensile deformation of nanocrystalline Ni foils under the effect of pulsed current was analyzed using TEM and TKD.It was found that the applied pulse current increased the activity of the nanocrystalline boundaries,promoted the movement of dislocations,and reduced the tendency of dislocation entanglement.The higher the peak current density and the smaller the angle between the direction of the current and the direction of deformation,the smaller the grain boundary orientation difference,the more dispersed the grain orientation,and the lower the density of geometrically necessary dislocations(GND)in the deformed nanocrystalline foil,the more significant the effect on material plasticity improvement.
基金support from the Key Program of the National Natural Science Foundation of China(No.12232004)the Training Program of the Sichuan Province Science and the Technology Innovation Seedling Project(No.MZGC20230012)are acknowledged.
文摘The development of modern engineering components and equipment features large size,intricate shape and long service life,which places greater demands on valid methods for fatigue performance analysis.Achieving a smooth transformation between small-scale laboratory specimens’fatigue properties and full-scale engineering components’fatigue strength has been a long-term challenge.In this work,two dominant factors impeding the smooth transformation—notch and size effect were experimentally studied,in which fatigue tests on Al 7075-T6511(a very high-strength aviation alloy)notched specimens of different scales were carried out.Fractography analyses identified the evidence of the size effect on notch fatigue damage evolution.Accordingly,the Energy Field Intensity(EFI)initially developed for multiaxial notch fatigue analysis was improved by utilizing the volume ratio of the Effective Damage Zones(EDZs)for size effect correction.In particular,it was extended to a probabilistic model considering the inherent variability of the fatigue phenomenon.The experimental data of Al 7075-T6511 notched specimens and the model-predicted results were compared,indicating the high potential of the proposed approach in fatigue evaluation under combined notch and size effects.
基金financial support from the National Key Research and Development Program of China(No.2021YFB3702101)National Natural Science Foundation of China(No.52130107,52071038)+5 种基金Fundamental Research Funds for the Central Universities(No.2023CDJXY-018)the“111”Project(No.B16007)by the Ministry of Education and the State Administration of Foreign Experts Affairs of Chinasupport to the Norwegian Micro-and Nano-Fabrication Facility,NorFab(No.295864)the Norwegian Laboratory for Mineral and Materials Characterization,MiMaC(No.269842/F50)the RCN INRPART project IntMat(No.309724)the Center for Research based Innovation SFI PhysMet(No.309584).
文摘Mg-3Gd(wt.%)samples with different initial grain sizes were prepared to evaluate the grain size effect on microstructural evolution during cold rolling and subsequent annealing hardening response.The deformation behavior and mechanical response of the as-rolled and annealed samples were systematically investigated by a combination of electron microscopy and microhardness characterization.The results show that the twinning activities were highly suppressed in the fine-grained samples during rolling.Upon increasing the rolling reduction to 40%,ultra-fine grain structures with a volume fraction of∼28%were formed due to the activation of multiple slip systems.Conversely,twinning dominated the early stages of deformation in the coarse-grained samples.After a 10%rolling reduction,numerous twins with a volume fraction of∼23%were formed.Further increasing the rolling reduction to 40%,high-density dislocations were activated and twin structures with a volume fraction of∼36%were formed.The annealing hardening response of deformed samples was effectively enhanced compared to that of the non-deformed samples,which was attributed to the enhanced Gd segregation along grain boundaries,twin boundaries and dislocation cores.Moreover,the grain size and rolling reduction were found to affect the microstructure evolution during annealing,resulting in a notable difference in the annealing hardening response of Mg-3Gd alloy between samples of different grain sizes deformed to different strains.These findings highlight the crucial importance of microstructural and processing parameters in the design of high-strength,cost-effective Mg alloys.
基金supported by the National Key Research and Develop-ment Pr0gram of China(Nos.2021YFA1501104 and 2023YFA1506802)the National Natural Science Foundation of China(No.22032001).
文摘Ethanol steam reforming(ESR)represents a promising route for sustainable hydrogen production,leveraging the high hydrogen content,renewability,and logistical advantages of ethanol.Although Ni-based catalysts are leading non-noble candidates for ESR,their practical deployment is hindered by compromised H_(2) production efficiency and rapid deactivation.In this work,we combined catalyst synthesis,kinetic analysis,and mechanistic investigation to elucidate the effectsof Ni particle size(3-9 nm)on ESR performance of Ni/CeO_(2) catalysts.These Ni/CeO_(2) catalysts were prepared via a citric acid-assisted coprecipitation method,and systematically characterized using complementary techniques,including high-resolution transmission electron microscopy(HRTEM),in situ X-ray photoelectron spectroscopy(XPS),hydrogen temperature-programmed reduction(H_(2)-TPR),Raman spectroscopy,O_(2)/CO chemisorption,and temperature-programmed surface reaction(TPSR)analyses.Mechanistic study revealed that ethanol dehydrogenation to acetaldehyde is the rate-determining step,defining the intrinsic activity of Ni sites,whereas C-C bond cleavage governs H_(2) selectivity in ESR.At smaller Ni sizes(e.g.,3.1 nm),larger CeO_(2) surface was exposed,which promoted acetaldehyde condensation to acetone,and consequently reduced H_(2) production efficiency.The Ni/CeO_(2) catalyst with~5 nm of Ni particles afforded the highest H_(2) yield(66.3%)and outstanding stability by balancing dehydrogenation activity,H_(2) selectivity,and coking resistance.Conversely,larger Ni particles(>6 nm)facilitated methanation reaction and catalyst deactivation.This work reconciles prior inconsistencies in the Ni size effects on ESR and provides guidance for the design of efficient and durable Ni-based catalysts for H_(2) production.
基金supported in part by the National Natural Science Foundation of China(No.52276009)。
文摘Accurate simulation of ice accretion of supercooled large droplet(SLD)is pivotal for the international airworthiness certification of large aircraft.Its complex dynamics behavior and broad particle size distributions pose significant challenges to reliable CFD predictions.A numerical model of multi-particle SLD coupling breaking,bouncing and splashing behaviors is established to explore the relationship between dynamics behavior and particle size.The results show that the peak value of droplet collection efficiencyβdecreases due to splashing.The bounce phenomenon will make the impact limit S_(m)of the water drops decrease.With the increase of the SLD particle size,the water drop bounce point gradually moves toward the trailing edge of the wing.The critical breaking diameter of SLD at an airflow velocity of 50 m/s is approximately 100μm.When the SLD particle size increases,the height of the water droplet shelter zone on the upper edge of the wing gradually decreases,and the velocity in the Y direction decreases first and then increases in the opposite direction,increasing the probability of SLD hitting the wing again.Large particle droplets have a higher effect on the impact limit S_(m)than smaller droplets.Therefore,in the numerical simulation of the SLD operating conditions,it is very important to ensure the proportion of large particle size water droplets.
基金financially supported by the National Science and Technology Major Project of China (No.J2019-VI-0004-0117)a Laboratory Fund Project (6142903220101)。
文摘The size and shape effect(SSE)of components has become a critical issue for mechanical properties,application reliability,and processing.In this study,the creep rupture life(CRL)of components with different wall thicknesses and positions in a combustion chamber casing simulator made of K439B superalloy was investigated.The intrinsic mechanisms of the SSE were explored from the dendrite structure,volume fraction and size of theγ'phase,and element segregation,etc.It is shown that this casting exhibits a strong SSE of creep rupture life,characterized by a significant difference in the CRL values up to 60%with the variation of wall thickness and position in the casing.In terms of casting technology,the influence of SSE on CRL is actually determined by the cooling rate.The SSE on the creep rupture life originates from the dendrite structure(such as the secondary dendrite arm spacing),volume fraction size of theγ'phase in the dendrite trunk,and elements segregation rate.This work may have implications for the design and application of engineering components with large sizes and complex structures.
文摘To understand the tensile deformation of electro-deposited Cu with nano-scale twins, a numerical study was carried out based on a conventional theory of mechanism-based strain gradient plasticity （CMSG）. The concept of twin lamella strengthening zone was used in terms of the cohesive interface model to simulate grain-boundary sliding and separation. The model included a number of material parameters, such as grain size, elastic modulus, plastic strain hardening exponent, initial yield stress, as well as twin lamellar distribution, which may contribute to size effects of twin layers in Cu polycrystalline. The results provide information to understand the mechanical behaviors of Cu with nano-scale growth twins.
基金This work was supported by the National Natural Science Foundation of China （No.20776089） and the New Century Excellent Talents Program of Ministry of Education （No.NCET-05-0783）. The State Key Laboratory of Polymer Materials Engineering in Sichuan University was acknowledged for providing dmol3 modules and Prof. Ying Xue, Xiang-yuan Li, and Quan Zhu were grateful for the useful discussions.
文摘The process and mechanism of the ligand volume controlled Pd（PR3）2 （PR3=PH3, PMe3, and PtBu3） oxidative addition with aryl bromide were investigated, using density functional theory method with the conductor-like screening model. Association pathway and dissocia-tion pathway were investigated by the comparison of several energies. The cleavage energy of Pd（PR3）2 complex was calculated, as well as the oxidative addition reaction barrier energy of Pd（PR3）n （n=1,2） with aryl bromide in N,N-dimethylformamide solvent. This study proved that the ligands volume possessed a great impact on the mechanism of oxidative addition： less bulky ligand palladium associated with aryl bromide via two donor ligands,but larger bulky ligand palladium coordinated via monoligand.
基金Project(51375113)supported by the National Natural Science Foundation of China
文摘Micro radial compression tests were carried out on cylindrical specimens of pure copper polycrystals with different grain sizes. Experimental results indicated that phenomena of decreasing forming force, increasing scatter of forming force and more irregular surface topography occurred with the increase of grain size. A modified surface model based on dislocations pile-up in surface layer grains, and a flow stress scattering formulation based on standard deviation and grain size distribution were proposed to analyze size effects on forming force in micro compression. The inhomogeneous deformation of surface layer grains was discussed by the main deformation manner of rotation. A good agreement with the experimental results was achieved.
文摘To investigate the effects of thickness and grain size on mechanical and deformation properties of C5210 phosphor bronze thin sheets, samples with different grain sizes were obtained through annealing heat treatment at different temperatures; and then tensile tests of samples with different thicknesses and grain sizes were conducted at room temperature. The results show that yield strength increases with decreasing thickness from 800 to 50 μm, but work hardening exponent and total elongation decrease, and a modified model was proposed to describe the relation between yield strength and thickness; yield strength decreases as the grain size increases, but work hardening exponent shows an increasing trend, total elongation increases to a peak and then decreases. Fracture morphology of tensile specimens was observed by SEM, which indicates that all tensile specimens are ductile fracture. The dimple intensity increases as the specimen thickness increases but reduces with the specimen grain size increasing.
基金Project(51174235)supported by the National Natural Science Foundation of China
文摘Hardness of materials depends significantly on the indentation size and grain/sub-grain size via microindentation and nanoindentation tests of high-purity tungsten with different structures.The grain boundary effect and indentation size effect were explored.The indentation hardness was fitted using the Nix-Gao model by considering the scaling factor.The results show that the scaling factor is barely correlated with the grain/sub-grain size.The interaction between the plastically deformed zone（PDZ） boundary and the grain/sub-grain boundary is believed to be the reason that leads to an increase of the measured hardness at the specific depths.Results also indicate that the area of the PDZ is barely correlated with the grain/sub-grain size,and the indentation hardness starts to stabilize once the PDZ expands to the dimension of an individual grain/sub-grain.
基金the National Natural Science Foundation of China (No. 50905144)the Program for New Century Excellent Talents in University, the Natural Science Basic Research Plan in Shaanxi Province (No. 2011JQ6004)the 111 Project (No. B08040) for the support given to this research
文摘Aluminum alloy （Al-alloy） thin-walled （D/t ＆gt; 20, diameter D, wall thickness t） bent tubes have attracted increasing applications in many industries with mass quantities and diverse specifications due to satisfying high strength to weigh ratio requirements of product manufacturing. However, due to nonlinear nature of bending with coupling effects of multiple factors, the similarity theory seems not applicable and there occurs a challenge for efficient and reliable evaluation of the bending formability of thin-walled tube with various bending specifications. Considering the unequal deformation and three major instabilities, the bending formability of thin-walled Al-alloy tube in changing tube sizes such as D and t are clarified via both the analytical and FE modeling/ simulations. The experiments of rotary draw bending are conducted to validate the theoretical models and further confirm ＇size effect＇ related bending formability. The major results show that （1） The anti-wrinkling capability of tube decreases with the larger D and smaller t, and the effect significance of t is larger than that of D even under rigid supports; （2） The wall thinning increases with the larger D and smaller t, and this tendency becomes much more obvious under rigid supports; （3） The cross-section deformation increases with the larger D and smaller t according to the analytical model obtained intrinsic relationship, while this tendency becomes opposite due to the nonlinear role of mandrel die; （4） The size factor D/t can be used as a nondimensional index to evaluate both the bending formability regarding the wall thinning and cross-section deformation.
基金financially supported by the National Natural Science Foundation of China (No. 51771147)
文摘Al-Mg-Si-Sc alloys with different Mg/Si ratio(<1.73 in wt.% vs>1.73 in wt.%) and different grain size(coarse grains vs ultrafine grains) were prepared, which allowed to investigate the grain size-dependent Mg/Si ratio effect on the microstructural evolution and concomitantly on the hardness and electrical conductivity when subjected to aging at 200℃. In the coarse-grained Al-Mg-Sc-Sc alloys, the β" precipitation within the grain interior and also the precipitation hardening were highly dependent on the Mg/Si ratio,while the electrical conductivity was slightly affected by the Mg/Si ratio. A promoted β" precipitation was found in the case of Si excess(Mg/Si ratio <1.73), much greater than in the case of Mg excess(Mg/Si ratio>1.73). While in the ultrafine-grained Al-Mg-Si-Sc alloys, the electrical conductivity rather than the hardness was more sensitive to the Mg/Si ratio. The alloy with Si excess displayed electrical conductivity much higher than its counterpart with Mg excess. This is rationalized by the grain boundary precipitation promoted by Si, which reduced the solute atoms and precipitates within the grain interior. Age softening was found in the ultrafine-grained alloy with Si excess, but the ultrafine-grained alloy with Mg excess held the hardness almost unchanged during the aging. The hardness-conductivity correlation is comprehensively discussed by considering the coupling effect of Mg/Si ratio and grain size. A strategy to simultaneously increase the hardness/strength and electrical conductivity is proposed for the Al-Mg-SiSc alloys, based on present understanding of the predominant factors on strengthening and conductivity,respectively.
基金The project, supported by the National Natural Science Foundation of China (19891180, 19925211) and by the Chinese Academy of Sciences (KJ951-1-201) and "Bai Ren" plan
文摘The influences of I,article size on the mechanical properties of the particulate metal matrix composite;are obviously displayed in the experimental observations. However, the phenomenon can not be predicted directly using the conventional elastic-plastic theory. It is because that no length scale parameters are involved in the conventional theory. In the present research, using the strain gradient plasticity theory, a systematic research of the particle size effect in the particulate metal matrix composite is carried out. The roles of many composite factors, such as: the particle size, the Young's modulus of the particle, the particle aspect ratio and volume fraction, as well as the plastic strain hardening exponent of the matrix material, are studied in detail. In order to obtain a general understanding for the composite behavior, two kinds of particle shapes, ellipsoid and cylinder, are considered to check the strength dependence of the smooth or non-smooth particle surface. Finally, the prediction results will be applied to the several experiments about the ceramic particle-reinforced metal-matrix composites. The material length scale parameter is predicted.
基金This study was supported by the Project of Scientific Innovation of the Chinese Academy of Sciences under contract No.ZKCX2-211the Science and Technology Plans of Shandong Province under contract No.022110107the Science and Technology Plans of Qingdao under contract No.03-1-HH-10.
文摘In 2002, six cohorts ofbroodstock bay scallop Argopecten irradians irradians （Ne=1, 2, 10, 30, 50 and control） were randomly chosen from a population of bay scallop to produce offspring. After one year rearing, with the progeny matured, the similar experiment was done to produce the F2 generation. To determine the magnitude of Ne effects, the growth and survival rates in larvae and adult of six F2 groups were compared. Results showed that inbreeding depression existed not only in the Ne=1 group but also in the Ne=2 group. The growth and survival rates of the two groups were significantly lower than those of the other groups （Ne=10, 30, 50, control）, and there were no significant differences among the latter （P〉0.05）. At the same time, the amount of depression in the Ne=1 group was significantly higher than that of the Ne=2 group （P〈0.05）. These results indicated that the low effective population size （Ne）, which increases the possibility of inbreeding, could lead to some harmful effects on the offspring. So it is essential to maintain a high level of Ne in commercial seed production. Fta＇thermore, as the high fecundity of bay scallop might lead to increased inbreeding, selecting broodstock from different growout sites is recommended.
基金the National Natural Science Foundation of China(Nos.U22A20166,51904190,12172230,11872258 and U19A2098)the Department of Science and Technology of Guangdong Province(No.2019ZT08G315)MOE Laboratory of Deep Earth Science and Engineering(No.DESE202102).
文摘Understanding the size effect exhibited by the fracture mechanism of anisotropic geomaterials is important for engineering practice. In this study, the anisotropic features of the nominal strength, apparent fracture toughness, effective fracture energy and fracture process zone(FPZ) size of geomaterials were first analyzed by systematic size effect fracture experiments. The results showed that the nominal strength and the apparent fracture toughness decreased with increasing bedding plane inclination angle.The larger the specimen size was, the smaller the nominal strength and the larger the apparent fracture toughness was. When the bedding inclination angle increased from 0° to 90°, the effective fracture energy and the effective FPZ size both first decreased and then increased within two complex variation stages that were bounded by the 45° bedding angle. Regardless of the inherent anisotropy of geomaterials,the nominal strength and apparent fracture toughness can be predicted by the energy-based size effect law, which demonstrates that geomaterials have obvious quasi-brittle characteristics. Theoretical analysis indicated that the true fracture toughness and energy dissipation can be calculated by linear elastic fracture mechanics only when the brittleness number is higher than 10;otherwise, size effect tests should be adopted to determine the fracture parameters.
基金Supported by National Natural Science Foundation of China (No.50638030, 50528808)the National Key Technologies R&D Program of China (No.2006BAJ13B02)the Australian Research Council (No.DP0774061).
文摘Numerical method is popular in analysing the blast wave propagation and interaction with structures.However,because of the extremely short duration of blast wave and energy trans-mission between different grids,the numerical results are sensitive to the finite element mesh size.Previous numerical simulations show that a mesh size acceptable to one blast scenario might not be proper for another case,even though the difference between the two scenarios is very small,indicating a simple numerical mesh size convergence test might not be enough to guarantee accu-rate numerical results.Therefore,both coarse mesh and fine mesh were used in different blast scenarios to investigate the mesh size effect on numerical results of blast wave propagation and interaction with structures.Based on the numerical results and their comparison with field test re-sults and the design charts in TM5-1300,a numerical modification method was proposed to correct the influence of the mesh size on the simulated results.It can be easily used to improve the accu-racy of the numerical results of blast wave propagation and blast loads on structures.
