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
Compared to traditional perovskite ferroelectric materials,HfO_(2) has emerged as a prominent research focus due to its ability to retain significant ferroelectricity at the nanoscale.However,systematic studies on its...Compared to traditional perovskite ferroelectric materials,HfO_(2) has emerged as a prominent research focus due to its ability to retain significant ferroelectricity at the nanoscale.However,systematic studies on its performance in thicker films remain limited,leaving the intrinsic relationship between thickness variation and ferroelectric properties poorly understood.In this work,we successfully fabricated doped HfO_(2)-based ferroelectric thin films with thicknesses spanning tens to hundreds of nanometers.All these films exhibit robust ferroelectric characteristics,and their ferroelectric properties demonstrate a non-monotonic evolution with increasing thickness.Macroscopic electrical measurements and mesoscale domain switching analysis confirmed that the ferroelectric properties of Ce:HfO_(2) films first diminish and then recover with the increase of film thickness.By further characterizing the evolution of microscopic structures,we elucidate the thickness effects on the grain size distribution and domain structure evolution.This framework clarifies the physical mechanism underlying the thickness-dependent ferroelectric behavior.Our findings provide critical experimental evidence for developing large-scale HfO_(2)-based ferroelectric devices and lay a theoretical foundation for optimizing thick-film ferroelectric materials for practical applications.展开更多
The systematic investigation of the mechanical properties and microstructure evolution process of ultra-thin-walled Inconel 718 capillary brazing joints is of great significance because of the exceptionally high deman...The systematic investigation of the mechanical properties and microstructure evolution process of ultra-thin-walled Inconel 718 capillary brazing joints is of great significance because of the exceptionally high demands on its application.To achieve this objective,this study investigates the impact of three distinct brazing temperatures and five typical grain sizes on the brazed joints’mechanical properties and microstructure evolution process.Microstructural evolution analysis was conducted based on Electron Back Scatter Diffraction(EBSD),Scanning Electron Microscopy(SEM),X-Ray Diffraction(XRD),High-Resolution Transmission Electron Microscopy(HRTEM),and Focused Ion Beam(FIB).Besides,the mechanical properties and fracture behavior were studied based on the uniaxial tension tests and in-situ tension tests.The findings reveal that the brazing joint’s strength is higher for the fine-grain capillary than the coarse-grain one,primarily due to the formation of a dense branch structure composed of G-phase in the brazing seam.The effects of grain size,such as pinning and splitting,are amplified at higher brazing temperatures.Additionally,micro-cracks initiate around brittle intermetallic compounds and propagate through the eutectic zone,leading to a cleavage fracture mode.The fracture stress of fine-grain specimens is higher than that of coarse-grain due to the complex micro-crack path.Therefore,this study contributes significantly to the literature by highlighting the crucial impact of grain size on the brazing properties of ultra-thin-walled Inconel 718 structures.展开更多
The macroscopic mechanical properties of rocks are significantly influenced by their microstructure.As a material bonded by mineral grains,the grain morphology of crystalline rock is the primary factor influencing the...The macroscopic mechanical properties of rocks are significantly influenced by their microstructure.As a material bonded by mineral grains,the grain morphology of crystalline rock is the primary factor influencing the strength.However,most strength criteria neglect the strength variations caused by different grain characteristics in rocks.Furthermore,the traditional linear criteria tend to overestimate tensile strength and exhibit apex singularity.To address these shortcomings,a piecewise strength criterion that considers the grain size effect has been proposed.A part of an ellipse was employed to construct the envelope of the tensive-shear region on the meridian plane,to accurately reproduce the low tensile-compressive strength ratio.Based on the analysis of experimental data,both linear and exponential modification functions that account for grain size effects were integrated into the proposed criterion.The corresponding finite element algorithm has been implemented.The accuracy and applicability of the proposed criterion were validated by comparing with the experimental data.展开更多
To provide insight into the effect of grain size on the precipitation behavior ofγstrengthening super-alloy Inconel 718,a gradient nanostructure with a large grain size span(from 9 nm to tens of microns)along the dep...To provide insight into the effect of grain size on the precipitation behavior ofγstrengthening super-alloy Inconel 718,a gradient nanostructure with a large grain size span(from 9 nm to tens of microns)along the depth direction was achieved by mean of surface mechanical grinding treatment,followed by annealing upon 700-1000℃ for 1 h.The results reveal significant differences in the type and size of precipitates in samples with different grain sizes.Noγprecipitate was detected inside the grains as the grain size was refined down to 40 nm(NG-40)and 9 nm(NG-9).Forδphase,a significantly accelerated precipitation along grain boundary was observed in NG-40 upon 700℃ annealing.Interestingly,with the grain size drops to 9 nm,the precipitation ofδwas suppressed,with some nanosized MC carbides appearing upon annealing.The grain size effect of precipitation behavior endows NG-9 an ultra-high RT-hardness(5.2 GPa)after 1000℃ thermal exposure and an ultra-high hot-hardness(3.2 GPa)at 800℃.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
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
In the present research, hierarchical structure observation and mechanical property characterization for a type of biomaterial are carried out. The investigated bioma- terial is Hyriopsis cumingii, a typical limnetic ...In the present research, hierarchical structure observation and mechanical property characterization for a type of biomaterial are carried out. The investigated bioma- terial is Hyriopsis cumingii, a typical limnetic shell, which consists of two different structural layers, a prismatic ＂pillar＂ structure and a nacreous ＂brick and mortar＂ structure. The prismatic layer looks like a ＂pillar forest＂ with variationsection pillars sized on the order of several tens of microns. The nacreous material looks like a ＂brick wall＂ with bricks sized on the order of several microns. Both pillars and bricks are composed of nanoparticles. The mechanical properties of the hierarchical biomaterial are measured by using the nanoindentation test. Hardness and modulus are measured for both the nacre layer and the prismatic layer, respectively. The nanoindentation size effects for the hierarchical structural materials are investigated experimentally. The results show that the prismatic nanostructured material has a higher stiffness and hardness than the nacre nanostructured material. In addition, the nanoindentation size effects for the hierarchical structural materials are described theoretically, by using the trans-scale mechanics theory considering both strain gradient effect and the surface/interface effect. The modeling results are consistent with experimental ones.展开更多
In order to study the indentation size effect(ISE)of germanium single crystals,nano-indentation experiments were carried out on the(100),(110)and(111)plane-orientated germanium single crystals.The true hardness of eac...In order to study the indentation size effect(ISE)of germanium single crystals,nano-indentation experiments were carried out on the(100),(110)and(111)plane-orientated germanium single crystals.The true hardness of each crystal plane of germanium single crystals was calculated based on the Meyer equation,proportional sample resistance(PSR)model and Nix-Gao model,and the indentation size effect(ISE)factor of each crystal plane was calculated.Results show that,the germanium single crystals experience elastic deformation,plastic deformation and brittle fracture during the loading process,and the three crystal planes all show obvious ISE phenomenon.All three models can effectively describe the ISE of germanium single crystals,and the calculated value of Nix-Gao model is the most accurate.Compared with the other two crystal planes,Ge(110)has the highest size effect factor m and the highest hardness,which indicates that Ge(110)has the worst plasticity.展开更多
Adopting the classical theory of hydrocodes,the constitutive relations of concretes are separated into an equation of state(EoS)which describes the volumetric behavior of concrete material and a strength model which d...Adopting the classical theory of hydrocodes,the constitutive relations of concretes are separated into an equation of state(EoS)which describes the volumetric behavior of concrete material and a strength model which depicts the shear properties of concrete.The experiments on the EoS of concrete is always challenging due to the technical difficulties and equipment limitations,especially for the specimen size effect on the EoS.Although some researchers investigate the shock properties of concretes by fly-plate impact tests,the specimens used in their tests are usually in one size.In this paper,the fly-plate impact tests on concrete specimens with different sizes are performed to investigate the size effect on the shock properties of concrete materials.The mechanical background of the size effect on the shock properties are revealed,which is related to the lateral rarefaction effect and the deviatoric stress produced in the specimen.According to the tests results,the modified EoS considering the size effect on the shock properties of concrete are proposed,which the bulk modulus of concrete is unpredicted by up to 20% if size effects are not accounted for.展开更多
There is a quantum spin Hall state in the inverted HgTe quantum well, characterized by the topologically protected gapless helical edge states lying within the bulk gap. It has been found that for a strip of finite wi...There is a quantum spin Hall state in the inverted HgTe quantum well, characterized by the topologically protected gapless helical edge states lying within the bulk gap. It has been found that for a strip of finite width, the edge states on the two sides can couple together to produce a gap in the spectrum. The phenomenon is called the finite size effect in quantum spin Hall systems. In this paper, we investigate the effects of the spin-orbit coupling due to bulk- and structure-inversion asymmetries on the finite size effect in the HgTe quantum well by means of the numerical diagonalization method. When the bulk-inversion asymmetry is taken into account, it is shown that the energy gap Eg of the edge states due to the finite size effect features an oscillating exponential decay as a function of the strip width of the HgTe quantum well. The origin of this oscillatory pattern on the exponential decay is explained. Furthermore, if the bulk- and structure-inversion asymmetries are considered simultaneously, the structure-inversion asymmetry will induce a shift of the energy gap Eg closing point. Finally, based on the roles of the bulk- and structure-inversion asymmetries on the finite size effects, a way to realize the quantum spin Hall field effect transistor is proposed.展开更多
It has been known that metal FeSiCr powders with large average particle sizes have been typically employed to prepare magnetic powder cores(SMCs),with few studies reported on the influence of magnetic properties for o...It has been known that metal FeSiCr powders with large average particle sizes have been typically employed to prepare magnetic powder cores(SMCs),with few studies reported on the influence of magnetic properties for original powders with various average particle sizes less than 10m.In this work,SiO_(2)-coated FeSiCr SMCs with different small particle sizes were synthesized using the sol-gel process.The contribution of SiO_(2)coating amount and voids to the soft magnetic properties was elaborated.The mechanism was revealed such that smaller particle sizes with less voids could be beneficial for reducing core loss in the SMCs.By optimizing the core structure,permeability and magnetic loss of 26 and 262 kW/cm^(3)at 100 kHz and 50 mT were achieved at a particle size of 4.8m and ethyl orthosilicate addition of 0.1 mL/g.The best DC stacking performance,reaching 87%,was observed at an ethyl orthosilicate addition rate of 0.25 mL/g under 100 Oe.Compared to other soft magnetic composites(SMCs),the FeSiCr/SiO_(2)SMCs exhibit significantly reduced magnetic loss.It further reduces the magnetic loss of the powder core,providing a new strategy for applications of SMCs at high frequencies.展开更多
Size effects are a well-documented phenomenon in heterogeneous catalysis,typically attributed to alterations in geometric and electronic properties.In this study,we investigate the influence of catalyst size in the pr...Size effects are a well-documented phenomenon in heterogeneous catalysis,typically attributed to alterations in geometric and electronic properties.In this study,we investigate the influence of catalyst size in the preparation of carbon nanotube(CNT)and the hydrogenation of 4,6-dinitroresorcinol(DNR)using Fe_(2)O_(3)and Pt catalysts,respectively.Various Fe_(2)O_(3)/Al_(2)O_(3)catalysts were synthesized for CNT growth through catalytic chemical vapor deposition.Our findings reveal a significant influence of Fe_(2)O_(3)nanoparticle size on the structure and yield of CNT.Specifically,CNT produced with Fe_(2)O_(3)/Al_(2)O_(3)containing 28%(mass)Fe loading exhibits abundant surface defects,an increased area for metal-particle immobilization,and a high carbon yield.This makes it a promising candidate for DNR hydrogenation.Utilizing this catalyst support,we further investigate the size effects of Pt nanoparticles on DNR hydrogenation.Larger Pt catalysts demonstrate a preference for 4,6-diaminoresorcinol generation at(100)sites,whereas smaller Pt catalysts are more susceptible to electronic properties.The kinetics insights obtained from this study have the potential to pave the way for the development of more efficient catalysts for both CNT synthesis and DNR hydrogenation.展开更多
FeS_(2) shows significant potential as cathode material for all-solid-state lithium batteries(ASSLBs)due to its high theoretical specific capacity,low cost,and environmental friendliness.However,the poor ion/electron ...FeS_(2) shows significant potential as cathode material for all-solid-state lithium batteries(ASSLBs)due to its high theoretical specific capacity,low cost,and environmental friendliness.However,the poor ion/electron conductivity and large volume variation effect of FeS_(2) inhibit its practical applications.Here,the influence of particle size of FeS_(2) on the corresponding sulfide-based solid-state batteries is carefully investigated by tuning FeS_(2) size.Moreover,low operating temperature is chosen to mitigate the large volume changes during cycling in the battery.S-FeS_(2) with smaller particle sizes delivers superior electrochemical performances than that of the larger L-FeS_(2) in Li_(5.5)PS_(4.5)Cl_(1.5)-based ASSLBs under different operating temperatures.S-FeS_(2) shows stable discharge capacities during 50 cycles with a current density of 0.1 m A/cm^(2)under -20℃.When the current density rises to 1.0 m A/cm^(2),it delivers an initial discharge capacity of 146.9 m Ah/g and maintains 63% of the capacity after 100 cycles.This work contributes to constructing ASSLBs enables excellent electrochemical performances under extreme operating temperatures.展开更多
Refractories have unique capabilities such as sustaining their shape and properties at extreme conditions such as the combination of high temperatures and thermal shock,contact with molten metals and slags and in some...Refractories have unique capabilities such as sustaining their shape and properties at extreme conditions such as the combination of high temperatures and thermal shock,contact with molten metals and slags and in some circumstances resistance to erosion from abrasive particles.Given the large processing output of the heavy industries such as the cement and steel ones which both require high temperature processes,the refractories structures span various meters and weight of several tons.As the water removal stage of hydraulic bonded castables in industrial sites takes hours(10-60 h)due to the risk of explosive spalling,efforts to mitigate it are commonly studied.This has provided theoretical understanding of the general aspects of drying and important tools,such as the thermogravimetry analysis(TGA),for the design of refractory compositions with higher explosive spalling resistance.However,the optimization of this process is still far from the industrial reality especially because the actual linings that require the drying are orders of magnitude larger than the samples considered in the laboratory tests.Therefore,this study proposed the analysis of the sample volume effect on the water removal dynamics through TGA of high alumina castables with calcium aluminate cement.Conventionalφ5 cm×5 cm cylindrical samples were assessed in a laboratory scale equipment whereas macro TGA were carried out considering 20 cm×20 cm×20 cm and 30 cm×30 cm×30 cm cubic samples.Additionally,the effect of polymeric fibers was also considered.It was found out that the different thermal gradients within the macro TGA samples resulted in an inflection on the sample’s heating rate and that the mass loss was affected by the volume considered,especially for the composition without additives.These findings highlight the requirement of carefully taking into consideration the different dimensional sizes and thermal gradients in the samples when analyzing and interpreting the laboratory studies,and especially when trying to extrapolate such results to the industrial reality.展开更多
Six kinds of micro bridge-beam specimens with different sizes are fabricated using photolithography technology for bending test. Beam specimens with trapezoidal section could be representatives of those with rectangle...Six kinds of micro bridge-beam specimens with different sizes are fabricated using photolithography technology for bending test. Beam specimens with trapezoidal section could be representatives of those with rectangle and square section, which are usually applied in MEMS. Nano indentation method used in bending test can be applied to both elastic and plastic materials. Also, some mechanical properties parameters such as the modulus of elasticity, hardness and the bending strength are obtained. The average modulus of elasticity of SCS is 170.295 0±2.485 0 GPa, showing no size effects, but the bending strength ranges from 3.24 GPa to 10.15 GPa, displaying strong size effects, and the average hardness is 9.496 7±1.753 3 GPa,in which no obvious size effects are observed.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
Projection micro stereolithography(PμSL)has emerged as a powerful three-dimensional(3D)printing technique for manufacturing polymer structures with micron-scale high resolution at high printing speed,which enables th...Projection micro stereolithography(PμSL)has emerged as a powerful three-dimensional(3D)printing technique for manufacturing polymer structures with micron-scale high resolution at high printing speed,which enables the production of customized 3D microlattices with feature sizes down to several microns.However,the mechanical properties of as-printed polymers were not systemically studied at the relevant length scales,especially when the feature sizes step into micron/sub-micron level,limiting its reliable performance prediction in micro/nanolattice and other metamaterial applications.In this work,we demonstrate that PμSL-printed microfibers could become stronger and significantly more ductile with reduced size ranging from 20μm to 60μm,showing an obvious size-dependent mechanical behavior,in which the size decreases to 20μm with a fracture strain up to~100%and fracture strength up to~100 MPa.Such size effect enables the tailoring of the material strength and stiffness of PμSL-printed microlattices over a broad range,allowing to fabricate the microlattice metamaterials with desired/tunable mechanical properties for various structural and functional applications.展开更多
Estimation of horizontal stress magnitudes from borehole breakouts has been an attractive topic in the petroleum and mining industries,although there are critical research gaps that remain unfilled.In this paper,numer...Estimation of horizontal stress magnitudes from borehole breakouts has been an attractive topic in the petroleum and mining industries,although there are critical research gaps that remain unfilled.In this paper,numerical simulation is conducted on Gosford sandstone to investigate the borehole breakout and its associated borehole size effect,including temperature influence.The discrete element method(DEM)model shows that the borehole breakout angular span is constant after the initial formation,whereas its depth propagates along the minimum horizontal stress direction.This indicates that the breakout angular span is a reliable parameter for horizontal stress estimation.The borehole size effect simulations illustrated the importance of borehole size on breakout geometries in which smaller borehole size leads to higher breakout initiation stress as well as the stress re-distribution from borehole wall outwards through micro-cracking.This implies that the stress may be averaged over a distance around the borehole and breakout initiation occurs at the borehole wall rather than some distance into the rock.In addition,the numerical simulation incorporated the thermal effect which is widely encountered in deep geothermal wells.Based on the results,the higher temperature led to lower breakout initiation stress with same borehole size,and more proportion of shear cracks was generated under higher temperature.This indicates that the temperature might contribute to the micro-fracturing mode and hence influences the horizontal stress estimation results from borehole breakout geometries.Numerical simulation showed that breakout shape and dimensions changed considerably under high stress and high temperature conditions,suggesting that the temperature may need to be considered for breakout stress analysis in deep locations.展开更多
In order to investigate the effect of sample size on the dynamic torsional behaviour of the 2A12 aluminium alloy. In this paper, torsional split Hopkinson bar tests are conducted on this alloy with different sample di...In order to investigate the effect of sample size on the dynamic torsional behaviour of the 2A12 aluminium alloy. In this paper, torsional split Hopkinson bar tests are conducted on this alloy with different sample dimensions. It is found that with the decreasing gauge length and thickness, the tested yield strength increases. However, the sample innerlouter diameter has little effect on the dynamic torsional behaviour. Based on the finite element method, the stress states in the alloy with different sample sizes are analysed. Due to the effect of stress concentration zone （SCZ）, the shorter sample has a higher yield stress. Furthermore, the stress distributes more uniformly in the thinner sample, which leads to the higher tested yield stress. According to the experimental and simulation analysis, some suggestions on choosing the sample size are given as well.展开更多
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supported by the National Natural Science Foundation of China(Nos.12372331,12072307,and 12302429)the Science and Technology Innovation Program of Hunan Province,China(No.2024RC3160)the Guangdong Basic and Applied Basic Research Foundation(No.2022A1515110116).
文摘Compared to traditional perovskite ferroelectric materials,HfO_(2) has emerged as a prominent research focus due to its ability to retain significant ferroelectricity at the nanoscale.However,systematic studies on its performance in thicker films remain limited,leaving the intrinsic relationship between thickness variation and ferroelectric properties poorly understood.In this work,we successfully fabricated doped HfO_(2)-based ferroelectric thin films with thicknesses spanning tens to hundreds of nanometers.All these films exhibit robust ferroelectric characteristics,and their ferroelectric properties demonstrate a non-monotonic evolution with increasing thickness.Macroscopic electrical measurements and mesoscale domain switching analysis confirmed that the ferroelectric properties of Ce:HfO_(2) films first diminish and then recover with the increase of film thickness.By further characterizing the evolution of microscopic structures,we elucidate the thickness effects on the grain size distribution and domain structure evolution.This framework clarifies the physical mechanism underlying the thickness-dependent ferroelectric behavior.Our findings provide critical experimental evidence for developing large-scale HfO_(2)-based ferroelectric devices and lay a theoretical foundation for optimizing thick-film ferroelectric materials for practical applications.
基金co-supported by the National Natural Science Foundation of China(No.52105316)the National Natural Foundation of Jiangxi,China(No.2021BAB214046)+1 种基金the Fundamental Research Funds for the Central Universities,China(No.501LKQB2022107021)Young Elite Scientists Sponsorship Program by the China Association for Science and Technology(No.YESS20200397)。
文摘The systematic investigation of the mechanical properties and microstructure evolution process of ultra-thin-walled Inconel 718 capillary brazing joints is of great significance because of the exceptionally high demands on its application.To achieve this objective,this study investigates the impact of three distinct brazing temperatures and five typical grain sizes on the brazed joints’mechanical properties and microstructure evolution process.Microstructural evolution analysis was conducted based on Electron Back Scatter Diffraction(EBSD),Scanning Electron Microscopy(SEM),X-Ray Diffraction(XRD),High-Resolution Transmission Electron Microscopy(HRTEM),and Focused Ion Beam(FIB).Besides,the mechanical properties and fracture behavior were studied based on the uniaxial tension tests and in-situ tension tests.The findings reveal that the brazing joint’s strength is higher for the fine-grain capillary than the coarse-grain one,primarily due to the formation of a dense branch structure composed of G-phase in the brazing seam.The effects of grain size,such as pinning and splitting,are amplified at higher brazing temperatures.Additionally,micro-cracks initiate around brittle intermetallic compounds and propagate through the eutectic zone,leading to a cleavage fracture mode.The fracture stress of fine-grain specimens is higher than that of coarse-grain due to the complex micro-crack path.Therefore,this study contributes significantly to the literature by highlighting the crucial impact of grain size on the brazing properties of ultra-thin-walled Inconel 718 structures.
基金Project(2023YFC2907403)supported by the National Key R&D Program of ChinaProject(52074021)supported by the National Natural Science Foundation of China+1 种基金Project(2242045)supported by Beijing Natural Science Foundation,ChinaProject(ZD202216)supported by the Beijing Association of Higher Education,China。
文摘The macroscopic mechanical properties of rocks are significantly influenced by their microstructure.As a material bonded by mineral grains,the grain morphology of crystalline rock is the primary factor influencing the strength.However,most strength criteria neglect the strength variations caused by different grain characteristics in rocks.Furthermore,the traditional linear criteria tend to overestimate tensile strength and exhibit apex singularity.To address these shortcomings,a piecewise strength criterion that considers the grain size effect has been proposed.A part of an ellipse was employed to construct the envelope of the tensive-shear region on the meridian plane,to accurately reproduce the low tensile-compressive strength ratio.Based on the analysis of experimental data,both linear and exponential modification functions that account for grain size effects were integrated into the proposed criterion.The corresponding finite element algorithm has been implemented.The accuracy and applicability of the proposed criterion were validated by comparing with the experimental data.
基金supported by the Strategic Pri-ority Research Program of the Chinese Academy of Sciences(No.XDB0510400)the National Natural Science Foundation of China(No.52225102)the Youth Innovation Promotion Association CAS(No.2023201).
文摘To provide insight into the effect of grain size on the precipitation behavior ofγstrengthening super-alloy Inconel 718,a gradient nanostructure with a large grain size span(from 9 nm to tens of microns)along the depth direction was achieved by mean of surface mechanical grinding treatment,followed by annealing upon 700-1000℃ for 1 h.The results reveal significant differences in the type and size of precipitates in samples with different grain sizes.Noγprecipitate was detected inside the grains as the grain size was refined down to 40 nm(NG-40)and 9 nm(NG-9).Forδphase,a significantly accelerated precipitation along grain boundary was observed in NG-40 upon 700℃ annealing.Interestingly,with the grain size drops to 9 nm,the precipitation ofδwas suppressed,with some nanosized MC carbides appearing upon annealing.The grain size effect of precipitation behavior endows NG-9 an ultra-high RT-hardness(5.2 GPa)after 1000℃ thermal exposure and an ultra-high hot-hardness(3.2 GPa)at 800℃.
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.
基金The research was supported by the National Basic Research Program of China (Grant 2012CB937500),the National Natural Science Foundation of China (Grants 91216108,11432014),and the CAS/SAFEA International Partnership Program for Creative Reserch Teams
文摘In the present research, hierarchical structure observation and mechanical property characterization for a type of biomaterial are carried out. The investigated bioma- terial is Hyriopsis cumingii, a typical limnetic shell, which consists of two different structural layers, a prismatic ＂pillar＂ structure and a nacreous ＂brick and mortar＂ structure. The prismatic layer looks like a ＂pillar forest＂ with variationsection pillars sized on the order of several tens of microns. The nacreous material looks like a ＂brick wall＂ with bricks sized on the order of several microns. Both pillars and bricks are composed of nanoparticles. The mechanical properties of the hierarchical biomaterial are measured by using the nanoindentation test. Hardness and modulus are measured for both the nacre layer and the prismatic layer, respectively. The nanoindentation size effects for the hierarchical structural materials are investigated experimentally. The results show that the prismatic nanostructured material has a higher stiffness and hardness than the nacre nanostructured material. In addition, the nanoindentation size effects for the hierarchical structural materials are described theoretically, by using the trans-scale mechanics theory considering both strain gradient effect and the surface/interface effect. The modeling results are consistent with experimental ones.
基金Project(51765027)supported by the National Natural Science Foundation of China.
文摘In order to study the indentation size effect(ISE)of germanium single crystals,nano-indentation experiments were carried out on the(100),(110)and(111)plane-orientated germanium single crystals.The true hardness of each crystal plane of germanium single crystals was calculated based on the Meyer equation,proportional sample resistance(PSR)model and Nix-Gao model,and the indentation size effect(ISE)factor of each crystal plane was calculated.Results show that,the germanium single crystals experience elastic deformation,plastic deformation and brittle fracture during the loading process,and the three crystal planes all show obvious ISE phenomenon.All three models can effectively describe the ISE of germanium single crystals,and the calculated value of Nix-Gao model is the most accurate.Compared with the other two crystal planes,Ge(110)has the highest size effect factor m and the highest hardness,which indicates that Ge(110)has the worst plasticity.
基金supported by the National Natural Science Foundation of China[Grant Nos.51938011 and 51908405]Australian Research Council。
文摘Adopting the classical theory of hydrocodes,the constitutive relations of concretes are separated into an equation of state(EoS)which describes the volumetric behavior of concrete material and a strength model which depicts the shear properties of concrete.The experiments on the EoS of concrete is always challenging due to the technical difficulties and equipment limitations,especially for the specimen size effect on the EoS.Although some researchers investigate the shock properties of concretes by fly-plate impact tests,the specimens used in their tests are usually in one size.In this paper,the fly-plate impact tests on concrete specimens with different sizes are performed to investigate the size effect on the shock properties of concrete materials.The mechanical background of the size effect on the shock properties are revealed,which is related to the lateral rarefaction effect and the deviatoric stress produced in the specimen.According to the tests results,the modified EoS considering the size effect on the shock properties of concrete are proposed,which the bulk modulus of concrete is unpredicted by up to 20% if size effects are not accounted for.
基金Project supported by the National Natural Science Foundation of China(Grant No.11274102)the Program for New Century Excellent Talents in Universities,China(Grant No.NCET-11-0960)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20134208110001)
文摘There is a quantum spin Hall state in the inverted HgTe quantum well, characterized by the topologically protected gapless helical edge states lying within the bulk gap. It has been found that for a strip of finite width, the edge states on the two sides can couple together to produce a gap in the spectrum. The phenomenon is called the finite size effect in quantum spin Hall systems. In this paper, we investigate the effects of the spin-orbit coupling due to bulk- and structure-inversion asymmetries on the finite size effect in the HgTe quantum well by means of the numerical diagonalization method. When the bulk-inversion asymmetry is taken into account, it is shown that the energy gap Eg of the edge states due to the finite size effect features an oscillating exponential decay as a function of the strip width of the HgTe quantum well. The origin of this oscillatory pattern on the exponential decay is explained. Furthermore, if the bulk- and structure-inversion asymmetries are considered simultaneously, the structure-inversion asymmetry will induce a shift of the energy gap Eg closing point. Finally, based on the roles of the bulk- and structure-inversion asymmetries on the finite size effects, a way to realize the quantum spin Hall field effect transistor is proposed.
基金supported by the National Natural Science Foundation of China(Grant Nos.U2230119 and U23A20567)2022 Central Guidance on Local Science and Technology Development Projects(Grant No.2022ZYDF073)Outstanding Youth Fund of Sichuan Province(Grant No.22JCQN0005).
文摘It has been known that metal FeSiCr powders with large average particle sizes have been typically employed to prepare magnetic powder cores(SMCs),with few studies reported on the influence of magnetic properties for original powders with various average particle sizes less than 10m.In this work,SiO_(2)-coated FeSiCr SMCs with different small particle sizes were synthesized using the sol-gel process.The contribution of SiO_(2)coating amount and voids to the soft magnetic properties was elaborated.The mechanism was revealed such that smaller particle sizes with less voids could be beneficial for reducing core loss in the SMCs.By optimizing the core structure,permeability and magnetic loss of 26 and 262 kW/cm^(3)at 100 kHz and 50 mT were achieved at a particle size of 4.8m and ethyl orthosilicate addition of 0.1 mL/g.The best DC stacking performance,reaching 87%,was observed at an ethyl orthosilicate addition rate of 0.25 mL/g under 100 Oe.Compared to other soft magnetic composites(SMCs),the FeSiCr/SiO_(2)SMCs exhibit significantly reduced magnetic loss.It further reduces the magnetic loss of the powder core,providing a new strategy for applications of SMCs at high frequencies.
基金financially supported by the National Key Research and Development Program of China(2022YFA1503504)the National Natural Science Foundation of China(22038003,22178100,22178101,and U22B20141)+3 种基金the Shanghai Pilot Program for Basic Research(22TQ1400100-15)the Innovation Program of Shanghai Municipal Education Commissionthe Program of Shanghai Academic/Technology Research Leader(21XD1421000)the Shanghai Science and Technology Innovation Action Plan(22JC1403800)。
文摘Size effects are a well-documented phenomenon in heterogeneous catalysis,typically attributed to alterations in geometric and electronic properties.In this study,we investigate the influence of catalyst size in the preparation of carbon nanotube(CNT)and the hydrogenation of 4,6-dinitroresorcinol(DNR)using Fe_(2)O_(3)and Pt catalysts,respectively.Various Fe_(2)O_(3)/Al_(2)O_(3)catalysts were synthesized for CNT growth through catalytic chemical vapor deposition.Our findings reveal a significant influence of Fe_(2)O_(3)nanoparticle size on the structure and yield of CNT.Specifically,CNT produced with Fe_(2)O_(3)/Al_(2)O_(3)containing 28%(mass)Fe loading exhibits abundant surface defects,an increased area for metal-particle immobilization,and a high carbon yield.This makes it a promising candidate for DNR hydrogenation.Utilizing this catalyst support,we further investigate the size effects of Pt nanoparticles on DNR hydrogenation.Larger Pt catalysts demonstrate a preference for 4,6-diaminoresorcinol generation at(100)sites,whereas smaller Pt catalysts are more susceptible to electronic properties.The kinetics insights obtained from this study have the potential to pave the way for the development of more efficient catalysts for both CNT synthesis and DNR hydrogenation.
基金supported by the National Key Research and Development Program(No.2021YFB2400300)the National Natural Science Foundation of China(No.52177214)supported by China Fujian Energy Devices Science and Technology Innovation Laboratory Open Fund(No.21C-OP202211)。
文摘FeS_(2) shows significant potential as cathode material for all-solid-state lithium batteries(ASSLBs)due to its high theoretical specific capacity,low cost,and environmental friendliness.However,the poor ion/electron conductivity and large volume variation effect of FeS_(2) inhibit its practical applications.Here,the influence of particle size of FeS_(2) on the corresponding sulfide-based solid-state batteries is carefully investigated by tuning FeS_(2) size.Moreover,low operating temperature is chosen to mitigate the large volume changes during cycling in the battery.S-FeS_(2) with smaller particle sizes delivers superior electrochemical performances than that of the larger L-FeS_(2) in Li_(5.5)PS_(4.5)Cl_(1.5)-based ASSLBs under different operating temperatures.S-FeS_(2) shows stable discharge capacities during 50 cycles with a current density of 0.1 m A/cm^(2)under -20℃.When the current density rises to 1.0 m A/cm^(2),it delivers an initial discharge capacity of 146.9 m Ah/g and maintains 63% of the capacity after 100 cycles.This work contributes to constructing ASSLBs enables excellent electrochemical performances under extreme operating temperatures.
基金the Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior-Brasil(CAPES)-Finance Code 001.The authors would like to thank the Fundacao de Amparo a Pesquisa do Estado de Sao Paulo-FAPESP(grant number:2021/00251-0).Finally,the authors are also greatly thankful for FIRE support to carry out this work.
文摘Refractories have unique capabilities such as sustaining their shape and properties at extreme conditions such as the combination of high temperatures and thermal shock,contact with molten metals and slags and in some circumstances resistance to erosion from abrasive particles.Given the large processing output of the heavy industries such as the cement and steel ones which both require high temperature processes,the refractories structures span various meters and weight of several tons.As the water removal stage of hydraulic bonded castables in industrial sites takes hours(10-60 h)due to the risk of explosive spalling,efforts to mitigate it are commonly studied.This has provided theoretical understanding of the general aspects of drying and important tools,such as the thermogravimetry analysis(TGA),for the design of refractory compositions with higher explosive spalling resistance.However,the optimization of this process is still far from the industrial reality especially because the actual linings that require the drying are orders of magnitude larger than the samples considered in the laboratory tests.Therefore,this study proposed the analysis of the sample volume effect on the water removal dynamics through TGA of high alumina castables with calcium aluminate cement.Conventionalφ5 cm×5 cm cylindrical samples were assessed in a laboratory scale equipment whereas macro TGA were carried out considering 20 cm×20 cm×20 cm and 30 cm×30 cm×30 cm cubic samples.Additionally,the effect of polymeric fibers was also considered.It was found out that the different thermal gradients within the macro TGA samples resulted in an inflection on the sample’s heating rate and that the mass loss was affected by the volume considered,especially for the composition without additives.These findings highlight the requirement of carefully taking into consideration the different dimensional sizes and thermal gradients in the samples when analyzing and interpreting the laboratory studies,and especially when trying to extrapolate such results to the industrial reality.
文摘Six kinds of micro bridge-beam specimens with different sizes are fabricated using photolithography technology for bending test. Beam specimens with trapezoidal section could be representatives of those with rectangle and square section, which are usually applied in MEMS. Nano indentation method used in bending test can be applied to both elastic and plastic materials. Also, some mechanical properties parameters such as the modulus of elasticity, hardness and the bending strength are obtained. The average modulus of elasticity of SCS is 170.295 0±2.485 0 GPa, showing no size effects, but the bending strength ranges from 3.24 GPa to 10.15 GPa, displaying strong size effects, and the average hardness is 9.496 7±1.753 3 GPa,in which no obvious size effects are observed.
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the financial support from Shenzhen Science and Technology Innovation Committee under the Grant Nos. JCYJ20170818103206501, Type C 202011033000145Changsha Municipal Science and Technology Bureau Project kh2201035supported by the City University of Hong Kong under the Grant No. 9667226
文摘Projection micro stereolithography(PμSL)has emerged as a powerful three-dimensional(3D)printing technique for manufacturing polymer structures with micron-scale high resolution at high printing speed,which enables the production of customized 3D microlattices with feature sizes down to several microns.However,the mechanical properties of as-printed polymers were not systemically studied at the relevant length scales,especially when the feature sizes step into micron/sub-micron level,limiting its reliable performance prediction in micro/nanolattice and other metamaterial applications.In this work,we demonstrate that PμSL-printed microfibers could become stronger and significantly more ductile with reduced size ranging from 20μm to 60μm,showing an obvious size-dependent mechanical behavior,in which the size decreases to 20μm with a fracture strain up to~100%and fracture strength up to~100 MPa.Such size effect enables the tailoring of the material strength and stiffness of PμSL-printed microlattices over a broad range,allowing to fabricate the microlattice metamaterials with desired/tunable mechanical properties for various structural and functional applications.
基金The work reported here is funded by Australian Coal Industry’s Research Program(ACARP)grant no.C26063.
文摘Estimation of horizontal stress magnitudes from borehole breakouts has been an attractive topic in the petroleum and mining industries,although there are critical research gaps that remain unfilled.In this paper,numerical simulation is conducted on Gosford sandstone to investigate the borehole breakout and its associated borehole size effect,including temperature influence.The discrete element method(DEM)model shows that the borehole breakout angular span is constant after the initial formation,whereas its depth propagates along the minimum horizontal stress direction.This indicates that the breakout angular span is a reliable parameter for horizontal stress estimation.The borehole size effect simulations illustrated the importance of borehole size on breakout geometries in which smaller borehole size leads to higher breakout initiation stress as well as the stress re-distribution from borehole wall outwards through micro-cracking.This implies that the stress may be averaged over a distance around the borehole and breakout initiation occurs at the borehole wall rather than some distance into the rock.In addition,the numerical simulation incorporated the thermal effect which is widely encountered in deep geothermal wells.Based on the results,the higher temperature led to lower breakout initiation stress with same borehole size,and more proportion of shear cracks was generated under higher temperature.This indicates that the temperature might contribute to the micro-fracturing mode and hence influences the horizontal stress estimation results from borehole breakout geometries.Numerical simulation showed that breakout shape and dimensions changed considerably under high stress and high temperature conditions,suggesting that the temperature may need to be considered for breakout stress analysis in deep locations.
基金Financial support is from the NSFC(Grant Nos.11602257,11472257,11272300,11572299)funded by the key subject"Computational Solid Mechanics"of the China Academy of Engineering Physics
文摘In order to investigate the effect of sample size on the dynamic torsional behaviour of the 2A12 aluminium alloy. In this paper, torsional split Hopkinson bar tests are conducted on this alloy with different sample dimensions. It is found that with the decreasing gauge length and thickness, the tested yield strength increases. However, the sample innerlouter diameter has little effect on the dynamic torsional behaviour. Based on the finite element method, the stress states in the alloy with different sample sizes are analysed. Due to the effect of stress concentration zone （SCZ）, the shorter sample has a higher yield stress. Furthermore, the stress distributes more uniformly in the thinner sample, which leads to the higher tested yield stress. According to the experimental and simulation analysis, some suggestions on choosing the sample size are given as well.
