The synergistic effect of low Gd+Mn additions on the evolution of microstructure and mechanical properties of Mg−xGd−0.8Mn alloy was investigated.Gd addition shows a strong grain refinement effect on the extruded Mg−x...The synergistic effect of low Gd+Mn additions on the evolution of microstructure and mechanical properties of Mg−xGd−0.8Mn alloy was investigated.Gd addition shows a strong grain refinement effect on the extruded Mg−xGd−0.8Mn alloy,and leads to a continuous decrease in the area fraction of basal texture grains and the corresponding maximum density of texture components.However,the maximum density of the basal texture components grows abruptly as Gd content increases to 6 wt.%.When the Gd content is below 6 wt.%,the asymmetry of the tensile and compressive yield of the alloy is negatively correlated to the Gd content due to grain refinement and texture weakening effects.Besides,the contribution of grain refinement to higher alloy yield strength is more significant than that of grain orientation.Compared with the extruded Mg−xGd alloy,the extruded Mg−xGd−0.8Mn alloy shows a lower limit composition point that corresponds to solid solution strengthening and plasticizing effect(2 wt.%and 4 wt.%).Finally,the trend of basal slip and prismatic slip resistance variations of the extruded Mg−xGd−0.8Mn alloys was predicted.展开更多
The microstructural evolution of a cold-rolled and intercritical annealed medium-Mn steel(Fe-0.10C-5Mn)was investigated during uniaxial tensile testing.In-situ observations under scanning electron microscopy,transmiss...The microstructural evolution of a cold-rolled and intercritical annealed medium-Mn steel(Fe-0.10C-5Mn)was investigated during uniaxial tensile testing.In-situ observations under scanning electron microscopy,transmission electron microscopy,and X-ray diffraction analysis were conducted to characterize the progressive transformation-induced plasticity process and associated fracture initiation mechanisms.These findings were discussed with the local strain measurements via digital image correlation.The results indicated that Lüders band formation in the steel was limited to 1.5%strain,which was mainly due to the early-stage martensitic phase transformation of a very small amount of the less stable large-sized retained austenite(RA),which led to localized stress concentrations and strain hardening and further retardation of yielding.The small-sized RA exhibited high stability and progressively transformed into martensite and contributed to a stably extended Portevin-Le Chatelier effect.The volume fraction of RA gradually decreased from 26.8%to 8.2%prior to fracture.In the late deformation stage,fracture initiation primarily occurred at the austenite/martensite and ferrite/martensite interfaces and the ferrite phase.展开更多
The tensile behavior of(Fe_(50)Mn_(30)Co_(10)Cr_(10))_(100-x)Si_(x)(x=0(Si0),2(Si2))metastable HEAs prepared by selective laser melting was studied at cryogenic temperatures.The results demonstrate that the addition o...The tensile behavior of(Fe_(50)Mn_(30)Co_(10)Cr_(10))_(100-x)Si_(x)(x=0(Si0),2(Si2))metastable HEAs prepared by selective laser melting was studied at cryogenic temperatures.The results demonstrate that the addition of Si leads to lattice distortion and a decrease in stacking fault energy,especially at 77 K,which significantly promotes transformation-induced plasticity(TRIP)in Si2 HEAs.The yield strength,tensile strength,and ductility of Si2 HEAs are 505.2 MPa,1364.1 MPa,and 19%,which are 43%,53% and 58% higher than those of Si0 alloy,respectively.TRIP is the main deformation mode,in addition to dislocation slip,and plays a key role in strengthening.The reinforced and continuously sustained TRIP maintains a dynamic strain distribution during deformation.Ultrahigh strain hardening greatly enhances the strength and ductility.展开更多
As a representative of the third generation advanced high-strength steels(AHSSs),medium Mn steels(MMS)have broad development prospects in the field of automobile manufacturing.MMS with typical austenite reversion trea...As a representative of the third generation advanced high-strength steels(AHSSs),medium Mn steels(MMS)have broad development prospects in the field of automobile manufacturing.MMS with typical austenite reversion treatment have a soft duplex microstructure,i.e.ferrite+austenite,presenting a high ductility but a low yield strength.Here we show that a flash heating and cooling after austenite reversion treatment can replace the ferrite with strong martensite,which greatly enhances the yield strength of a 0.25C-4Mn steel by about 461–886 MPa.By adjusting the reversion temperature before the flash treatment,the C and Mn concentrations of reverted austenite can be altered,which determine the fraction of reverted austenite surviving the flash treatment.In addition,the mechanical stability of final retained austenite is also linked to the reversion temperature,resulting different work hardening behaviors due to transformation induced plasticity(TRIP)effect.By tweaking the reversion temperature before the flash treatment,an optimized combination of strength and ductility can be achieved.The micromechanical differences caused by the replacement of the matrix are also investigated via in-situ digital image correlation method.展开更多
To provide data for improved modelling of the behaviour of steel components in a simultaneous forming and quenching process, the effects of plastic deformation and stresses on dilatation during the martensitic transfo...To provide data for improved modelling of the behaviour of steel components in a simultaneous forming and quenching process, the effects of plastic deformation and stresses on dilatation during the martensitic transformation in a B-bearing steel were investigated. It was found that plastic deformation of austenite at high temperatures enhances ferrite formation significantly, and consequently, the dilatation decreases markedly even at a cooling rate of 280'C/s. The created ferritic-martensitic microstructure possesses clearly lower hardness and strength than the martensitic structure. Elastic stresses cause the preferred orientation in martensite to be formed so that diametric dilatation can increase by nearly 200% under axial compression.展开更多
In our previous study, metals have been used as absorbers in the clear plastic laser transmission welding. The effects of metal thermal conductivity on the welding quality are investigated in the present work. Four me...In our previous study, metals have been used as absorbers in the clear plastic laser transmission welding. The effects of metal thermal conductivity on the welding quality are investigated in the present work. Four metals with distinctly different thermal conductivities, i.e., titanium, nickel, molybdenum, and copper, are selected as light absorbers. The lap welding is conducted with an 808 nm diode laser and simulation experiments are also conducted. Nickel electroplating test is carried out to minimize the side-effects from different light absorptivities of different metals. The results show that the welding with an absorber of higher thermal conductivity can accommodate higher laser input power before smoking, which produces a wider and stronger welding seam.The positive role of the higher thermal conductivity can be attributed to the fact that a desirable thermal field distribution for the molecular diffusion and entanglement is produced from the case with a high thermal conductivity.展开更多
The Bauschinger and size effects in the thinfilm plasticity theory arising from the defect-energy of geometrically necessary dislocations （GNDs） are analytically investigated in this paper. Firstly, this defect-ener...The Bauschinger and size effects in the thinfilm plasticity theory arising from the defect-energy of geometrically necessary dislocations （GNDs） are analytically investigated in this paper. Firstly, this defect-energy is deduced based on the elastic interactions of coupling dislocations （or pile-ups） moving on the closed neighboring slip plane. This energy is a quadratic function of the GNDs density, and includes an elastic interaction coefficient and an energetic length scale L. By incorporating it into the work- conjugate strain gradient plasticity theory of Gurtin, an energetic stress associated with this defect energy is obtained, which just plays the role of back stress in the kinematic hardening model. Then this back-stress hardening model is used to investigate the Bauschinger and size effects in the tension problem of single crystal Al films with passivation layers. The tension stress in the film shows a reverse dependence on the film thickness h. By comparing it with discrete-dislocation simulation results, the length scale L is determined, which is just several slip plane spacing, and accords well with our physical interpretation for the defect- energy. The Bauschinger effect after unloading is analyzed by combining this back-stress hardening model with a friction model. The effects of film thickness and pre-strain on the reversed plastic strain after unloading are quantified and qualitatively compared with experiment results.展开更多
Polymers with reversible plasticity shape memory effect(RPSME)have attracted considerable attention due to their simple programming and large deformation.However,the exact mechanisms of RPSME are still not thoroughly ...Polymers with reversible plasticity shape memory effect(RPSME)have attracted considerable attention due to their simple programming and large deformation.However,the exact mechanisms of RPSME are still not thoroughly understood.In this work,the RPSME of SEBS/crystallizable paraffin was investigated by comparatively analyzing the performances and microstructures of samples with different paraffin content.It was found the shape fixing ratios(Rfs)of samples increased with the paraffin content,and interestingly,a significant improvement in Rf was observed when the paraffin content exceeded 60 wt%.Tensile test results showed that the deformation characteristics of samples changed from elastic to plastic as the paraffin content increased above 60 wt%.By exploring the crystallization behaviors of paraffin in various SEBS/paraffin samples,it was revealed that the microstructures of SEBS/paraffin were different when the paraffin content was below 50 wt%and above 60 wt%.In samples with low paraffin content(below 50 wt%),nearly all paraffin was co-crystallized with ethylene-co-butylene(EB)chains and its crystallization was severely restricted;while in samples with high paraffin content(above 60 wt%),“excess”paraffin appeared and this part of paraffin crystallized on the template of the EB/paraffin co-crystals,which might be responsible for the elastic-to-plastic transition and the sharp increase in Rf.Based on the above results,a possible structural model was proposed to explain the exact mechanism of RPSME in SEBS/paraffin.展开更多
Composite solid electrolytes(CSEs) containing polymer matrices and inorganic fillers hold promise for the next generation of solid-state batteries.However,the role of residual solvents in CSEs remains controversial.Th...Composite solid electrolytes(CSEs) containing polymer matrices and inorganic fillers hold promise for the next generation of solid-state batteries.However,the role of residual solvents in CSEs remains controversial.This study investigated the evolution and function of the residual solvent in a polymer-Li_2B_(12)H_(12) CSE.A partial reaction occurred between Li_2B_(12)H_(12) and solvent N,N-dimethylformamide(DMF),which produced dimethylaminomethanol(DMAM) in the CSE.Density functional theory calculations have revealed that DMA M forms stronger hydrogen bonds with polyvinylidene fluoride chains than DMF,which can have a plasticizing effect on the polymer matrix,leading to lower crystallinity and quicker segment motion.Therefore,this CSE exhibited improved Li-ion conducting properties,enabling the stable cycling of Li‖LiFePO_(4) solid-state batteries.This study provided insights into the role of residual solvents in CSEs.展开更多
A medium-carbon low-alloy steel with designed chemical composition was investigated.The steel exhibits an excellent product of strength and elongation value of 31,832 MPa%through quenching and partitioning treatment,w...A medium-carbon low-alloy steel with designed chemical composition was investigated.The steel exhibits an excellent product of strength and elongation value of 31,832 MPa%through quenching and partitioning treatment,with a tensile strength of 1413 MPa and elongation of 22%.X-ray diffraction analysis and transmission electron microscopy characterizations confirm that the retained austenite in the specimens undergoes stress-induced phase transformation to the martensite and hexagonal phases,namely the transformation-induced plasticity(TRIP)effect is triggered.This TRIP effect,triggered by the stress-induced phase transition of retained austenite,is responsible for the excellent mechanical properties obtained in the steel.For further investigating the stress-induced phase transition mechanism,thermodynamic methods are applied.Gibbs free energy of face-centered cubic-Fe,ε-Fe,ω-Fe and body-centered cubic-Fe associated with the stress-induced phase transition was calculated using molecular dynamics simulations,and a calculation method of strain energy in thermodynamic units for the stress-induced martensitic transformation is presented.The final results reveal the process and thermodynamic mechanism of stress-induced martensitic transformation in medium-carbon steels,in which the hexagonal phase can participate in the process as an intermediate product.展开更多
In order to explore the dependence of plasticity of metallic material on a high magnetic held,the effects of the different magnetic induction intensities（H = 0 T,0.5 T,1 T,3 T,and 5 T） and pulses number（N = 0,10,20...In order to explore the dependence of plasticity of metallic material on a high magnetic held,the effects of the different magnetic induction intensities（H = 0 T,0.5 T,1 T,3 T,and 5 T） and pulses number（N = 0,10,20,30,40,and 50） on tensile strength（σ;） and elongation（δ） of 2024 aluminum alloy are investigated in the synchronous presences of a high magnetic held and external stress.The results show that the magnetic held exerts apparent and positive effects on the tensile properties of the alloy.Especially under the optimized condition of H;=1 T and N;=30,the σ;and 8 are 410 MPa and 17% that are enhanced by 9.3% and 30.8% respectively in comparison to those of the untreated sample.The synchronous increases of tensile properties are attributed to the magneto-plasticity effect on a quantum scale.That is,the magnetic held will accelerate the state conversion of radical pair generated between the dislocation and obstacles from singlet to the triplet state.The bonding energy between them is meanwhile lowered and the moving flexibility of dislocations will be enhanced.At H;= 1 T and N;= 30,the dislocation density is enhanced by 1.28 times.The relevant minimum grain size is 266.1 nm,which is reduced by 35.2%.The grain rehning is attributed to the dislocation accumulation and subsequent dynamic recrystallization.The（211） and（220） peak intensities are weakened.It is deduced that together with the recrystallization,the hne grains will transfer towards the slip plane and contribute to the slipping deformation.展开更多
The intercritical annealing treatment at 650 and 700 ℃ results in two ultrafine-grained (UFG) dual-phase ferrite-austenitesteels. The two steels exhibit different and special discontinuous yielding and pronounced L&#...The intercritical annealing treatment at 650 and 700 ℃ results in two ultrafine-grained (UFG) dual-phase ferrite-austenitesteels. The two steels exhibit different and special discontinuous yielding and pronounced Lüders-like strain phenomenawith large yielding strain which are related to their retained γ-austenite (RA) volume fractions and RA stabilities. The steelannealed at 650 ℃ shows an absent or very small strain hardening, while the steel annealed at 700 ℃ shows an obviousstrain hardening upward curvature with increasing strain. The results show that before and during straining, the steel annealedat 650 ℃ exhibits a mixture of equiaxed and elongated UFG α-ferrite and austenite phases;however, the steel annealed at700 ℃ exhibits only elongated UFG α and γ phases. It was found that most of the γ-austenite to α′-martensite transformationoccurred at the initial deformation stage and very small or almost no transformation occurred afterward. This demonstratesthat the strain-induced martensite (SIM) transformation (γ-α′) or transformation-induced plasticity (TRIP) effect dominatesonly at the initial deformation stage. RA remained stable, and no TRIP effect was observed at the final deformation stage. Theload-unload-reload test was performed to evaluate the back stress (σb) hardening effect. It is believed that the pronouncedstrain hardening behavior at the later deformation stage is mainly associated with σb enhancement induced by the strainpartitioning between the soft and hard phases due to SIM transformation during tensile deformation.展开更多
The microstructures and mechanical properties of ferrite-based lightweight steel with different compositions were investigated by tensile test,scanning electron microscopy（SEM）,transmission electron microscopy（TEM...The microstructures and mechanical properties of ferrite-based lightweight steel with different compositions were investigated by tensile test,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray diffraction（XRD）and thermodynamic calculation（TC）.It was shown that the ferrite-based lightweight steels with 5wt.%or 8wt.%Al were basically composed of ferrite,austenite andκ-carbide.As the annealing temperature increased,the content of the austenite in the steel gradually increased,while theκ-carbide gradually decomposed and finally disappeared.The mechanical properties of the steel with 5wt.%Al and 2wt.%Cr,composed of ferrite and Cr7C3carbide at different annealing temperatures,were significantly inferior to those of others.The steel containing 5wt.%Al,annealed at 820°C for 50sthen rapidly cooled to 400°C and held for 180s,can obtain the best product of strength and elongation（PSE）of 31242MPa·%.The austenite stability of the steel is better,and its PSE is higher.In addition,the steel with higher PSE has a more stable instantaneous strain hardening exponent（n value）,which is mainly caused by the effect of transformation induced plasticity（TRIP）.When theκ-carbide or Cr7C3carbide existed in the microstructure of the steel,there was an obvious yield plateau in the tensile curve,while its PSE decreased significantly.展开更多
To explore the cumulative deformation effect of the dynamic response of a tunnel crossing the hauling sliding surface under earthquakes,the shaking table test was conducted in this study.Combined with the numerical ca...To explore the cumulative deformation effect of the dynamic response of a tunnel crossing the hauling sliding surface under earthquakes,the shaking table test was conducted in this study.Combined with the numerical calculations,this study proposed magnification of the Arias intensity(MIa)to characterize the overall local deformation damage of the tunnel lining in terms of the deformation characteristics,frequency domain,and energy.Using the time‐domain analysis method,the plastic effect coefficient(PEC)was proposed to characterize the degree of plastic deformation,and the applicability of the seismic cumulative failure effect(SCFE)was discussed.The results show that the low‐frequency component(f1 and f2≤10 Hz)and the high‐frequency component(f3 and f4>10 Hz)acceleration mainly cause global and local deformation of the tunnel lining.The local deformation caused by the high‐frequency wave has an important effect on the seismic damage of the lining.The physical meaning of PEC is more clearly defined than that of the residual strain,and the SCFE of the tunnel lining can also be defined.The SCFE of the tunnel lining includes the elastic deformation effect stage(<0.15g),the elastic–plastic deformation effect stage(0.15g–0.30g),and the plastic deformation effect stage(0.30g–0.40g).This study can provide valuable theoretical and technical support for the construction of traffic tunnels in high‐intensity earthquake areas.展开更多
Development of high-performance phase transformation electrodes in lithium ion batteries requires comprehensive studies on stress-mediated lithiation involving migration of the phase interface. It brings out many coun...Development of high-performance phase transformation electrodes in lithium ion batteries requires comprehensive studies on stress-mediated lithiation involving migration of the phase interface. It brings out many counter-intuitive phenomena, especially in nanoscale electrodes, such as the slowing down migration of phase interface, the vanishing of miscibility gap under high charge rate, and the formation of surface crack during lithiation. However, it is still a challenge to simulate the evolution of stress in arbitrarily-shaped nanoscale electrodes, accompanied with phase transformation and concurrent plastic deformation. This article gives a brief review of our efforts devoted to address these issues by developing phase field model and simulation. We demonstrate that the miscibility gap of two-phase state is affected not only by stress but also by surface reaction rate and particle size. In addition, the migration of phase interface slows down due to stress. It reveals that the plastic deformation generates large radial expansion, which is responsible for the transition from surface hoop compression to surface hoop tension that may induce surface crack during lithiation. We hope our effort can make a contribution to the understanding of stress-coupled kinetics in phase transformation electrodes.展开更多
The Luders deformation behavior in a medium Mn transformation induced plasticity （TRIP） steel is investigated at different temperatures ranging from 25 to 300 ℃. It demonstrates that the Ltiders band appears at all...The Luders deformation behavior in a medium Mn transformation induced plasticity （TRIP） steel is investigated at different temperatures ranging from 25 to 300 ℃. It demonstrates that the Ltiders band appears at all testing temperatures but with varied Luders strains which do not change monoton ically with temperature. The martensitic transformation is simultaneously observed within the Ltiders band in varying degrees depending on the testing temperature. It is well verified that the martensitic transformation is not responsible for the formation of Luders band, and a reasonable explanation is given for the non-monotonic variation of Luders strain with increasing temperature.展开更多
As metallic foams used for energy absorption in the automotive and aerospace industries, recently invented lotus-type porous metals are viewed as potential energy absorbers. Yet, solid conclusion on their eligibility ...As metallic foams used for energy absorption in the automotive and aerospace industries, recently invented lotus-type porous metals are viewed as potential energy absorbers. Yet, solid conclusion on their eligibility as energy absorbers is still in question, particularly when compression is in the direction perpendicular to the axial orientation of cylindrical pores. In this work, the energy absorption of lotus-type porous coppers in the perpendicular direction is investigated at strain rates from 0.001 s^（-1） to^2400 s^（-1）. The energy absorption capacity and the energy absorption efficiency are calculated to be4–16 k J/kg and 0.32–0.7, respectively, slightly inferior to metal foams and the same porous solid compressed in the parallel direction due to the shortened extent of the plateau stress region. The deformation mechanism is examined experimentally in conjunction with finite element modeling. Both suggest that gradual squeeze and collapse of pores are the mechanisms accommodating the energy absorption. The deformation is generally evenly distributed over pore ligaments and independent of strain rate.展开更多
In the present study, films and coatings for food applications based on a gum exudate from Brea tree （Cercidium praecox） were formulated and the influence of plasticizer content on their functional properties was ev...In the present study, films and coatings for food applications based on a gum exudate from Brea tree （Cercidium praecox） were formulated and the influence of plasticizer content on their functional properties was evaluated. Brea gum is a renewable resource available in semi-desert areas, extracted by native people. Films were produced by casting method and characterized through water vapour permeability, mechanical （tensile strength and elongation at break）, morphological and optical properties. Glycerol was used as plasticizer. Brea gum films presented good visual aspect, transparency and amber colour. Microscopic observation showed a dense and homogeneous structure. Film wettability increased with glycerol content due to hydrophilic nature of the plasticizer. Solubility of films in water increased with temperature. Water sorption isotherms of films at 25 ~C showed that at high aw （above 0.50）, the film matrix swells altering its structure and properties. Water vapour permeability remained practically constant up to 20% of glycerol content and then increases linearly with the plasticizer. The addition of glycerol decreased the opacity and tensile strength. The best film properties were obtained at 20% of glycerol concentration.展开更多
We introduce a non-equiatomic Fe_(61)Mn_(18)Si_(11)Cr_(10) medium entropy alloy designed by subjecting it to transformation-induced plasticity upon deformation at room temperature. Microstructure characterization carr...We introduce a non-equiatomic Fe_(61)Mn_(18)Si_(11)Cr_(10) medium entropy alloy designed by subjecting it to transformation-induced plasticity upon deformation at room temperature. Microstructure characterization carried out using scanning electron microscopy(SEM), electron backscatter diffraction(EBSD), transmission electron microscopy(TEM) and X-ray diffraction(XRD) shows a homogeneous solid solution FCC + BCC structured dual phase. Investigations on the deformation substructures at specific strain levels via EBSD reveal the deformation-induced transformations of γ→α′ and γ→ ε. The strengths, particularly yield strength, of the designed alloy are found to be higher than these of the well-studied five component FeMnNiCoCr system for the introduction of the hard phase( α′-martensite). When tensile tests are performed at different strain rates of 10^(–4)s^(-1), 10^(–3)s^(-1), 10^(–2)s^(-1), the tested material exhibits a slightly negative strain rate sensitivity and work hardening rate sensitivity.展开更多
In the present study,the performance of reinforced concrete tunnel(RCT)under internal water pressure is evaluated by using nonlinear finite element analysis and surrogate models.Several parameters,including the compre...In the present study,the performance of reinforced concrete tunnel(RCT)under internal water pressure is evaluated by using nonlinear finite element analysis and surrogate models.Several parameters,including the compressive and tensile strength of concrete,the size of the longitudinal reinforcement bar,the transverse bar diameter,and the internal water pre ssure,are considered as the input variables.Based on the levels of variables,36 mix designs are selected by the Taguchi method,and 12 mix designs are proposed in this study.Carbon fiber reinforced concrete(CFRC)or glass fiber reinforced concrete(GFRC)is considered for simulating these 12 samples.Principal component regression(PCR),Multi Ln equation regression(MLnER),and gene expression programming(GEP)are employed for predicting the percentage of damaged surfaces(PDS)of the RCT,the effective tensile plastic strain(ETPS),the maximum deflection of the RCT,and the deflection of crown of RCT.The error terms and statistical parameters,including the maximum positive and negative errors,mean absolute percentage error(MAPE),root mean square error(RMSE),coefficient of determination,and normalized square error(NMSE),are utili zed to evaluate the accuracy of the models.Based on the results,GEP performs better than other models in predicting the outputs.The results sh ow that the internal water pressure and the mechanical properties of concrete have the most effect on the damag e and deflection of the RCT.展开更多
基金National Natural Science Foundation of China(No.U2241231)National Key Research and Development Program of China(No.2021YFB3701100)+1 种基金Scientific Research Project of Jiangxi Provincial Department of Education,China(No.GJJ211038)Doctoral Research Project of Jinggangshan University,China(No.JZB2110)。
文摘The synergistic effect of low Gd+Mn additions on the evolution of microstructure and mechanical properties of Mg−xGd−0.8Mn alloy was investigated.Gd addition shows a strong grain refinement effect on the extruded Mg−xGd−0.8Mn alloy,and leads to a continuous decrease in the area fraction of basal texture grains and the corresponding maximum density of texture components.However,the maximum density of the basal texture components grows abruptly as Gd content increases to 6 wt.%.When the Gd content is below 6 wt.%,the asymmetry of the tensile and compressive yield of the alloy is negatively correlated to the Gd content due to grain refinement and texture weakening effects.Besides,the contribution of grain refinement to higher alloy yield strength is more significant than that of grain orientation.Compared with the extruded Mg−xGd alloy,the extruded Mg−xGd−0.8Mn alloy shows a lower limit composition point that corresponds to solid solution strengthening and plasticizing effect(2 wt.%and 4 wt.%).Finally,the trend of basal slip and prismatic slip resistance variations of the extruded Mg−xGd−0.8Mn alloys was predicted.
基金supported by the National Key R&D Program of China(No.2017YFB0304402)。
文摘The microstructural evolution of a cold-rolled and intercritical annealed medium-Mn steel(Fe-0.10C-5Mn)was investigated during uniaxial tensile testing.In-situ observations under scanning electron microscopy,transmission electron microscopy,and X-ray diffraction analysis were conducted to characterize the progressive transformation-induced plasticity process and associated fracture initiation mechanisms.These findings were discussed with the local strain measurements via digital image correlation.The results indicated that Lüders band formation in the steel was limited to 1.5%strain,which was mainly due to the early-stage martensitic phase transformation of a very small amount of the less stable large-sized retained austenite(RA),which led to localized stress concentrations and strain hardening and further retardation of yielding.The small-sized RA exhibited high stability and progressively transformed into martensite and contributed to a stably extended Portevin-Le Chatelier effect.The volume fraction of RA gradually decreased from 26.8%to 8.2%prior to fracture.In the late deformation stage,fracture initiation primarily occurred at the austenite/martensite and ferrite/martensite interfaces and the ferrite phase.
基金supported by Program for Innovative Research Team in Science and Technology in Fujian Province University,Chinathe Natural Science Foundation of Fujian Province,China(Nos.2023J011013,2020J01898)。
文摘The tensile behavior of(Fe_(50)Mn_(30)Co_(10)Cr_(10))_(100-x)Si_(x)(x=0(Si0),2(Si2))metastable HEAs prepared by selective laser melting was studied at cryogenic temperatures.The results demonstrate that the addition of Si leads to lattice distortion and a decrease in stacking fault energy,especially at 77 K,which significantly promotes transformation-induced plasticity(TRIP)in Si2 HEAs.The yield strength,tensile strength,and ductility of Si2 HEAs are 505.2 MPa,1364.1 MPa,and 19%,which are 43%,53% and 58% higher than those of Si0 alloy,respectively.TRIP is the main deformation mode,in addition to dislocation slip,and plays a key role in strengthening.The reinforced and continuously sustained TRIP maintains a dynamic strain distribution during deformation.Ultrahigh strain hardening greatly enhances the strength and ductility.
基金National Key R&D Program of China(Grant Nos.2022YFE0110800 and 2022YFB3705300)the National Natural Science Foundation of China(Grant Nos.52104380 and 52171123)for grant and financial support.
文摘As a representative of the third generation advanced high-strength steels(AHSSs),medium Mn steels(MMS)have broad development prospects in the field of automobile manufacturing.MMS with typical austenite reversion treatment have a soft duplex microstructure,i.e.ferrite+austenite,presenting a high ductility but a low yield strength.Here we show that a flash heating and cooling after austenite reversion treatment can replace the ferrite with strong martensite,which greatly enhances the yield strength of a 0.25C-4Mn steel by about 461–886 MPa.By adjusting the reversion temperature before the flash treatment,the C and Mn concentrations of reverted austenite can be altered,which determine the fraction of reverted austenite surviving the flash treatment.In addition,the mechanical stability of final retained austenite is also linked to the reversion temperature,resulting different work hardening behaviors due to transformation induced plasticity(TRIP)effect.By tweaking the reversion temperature before the flash treatment,an optimized combination of strength and ductility can be achieved.The micromechanical differences caused by the replacement of the matrix are also investigated via in-situ digital image correlation method.
文摘To provide data for improved modelling of the behaviour of steel components in a simultaneous forming and quenching process, the effects of plastic deformation and stresses on dilatation during the martensitic transformation in a B-bearing steel were investigated. It was found that plastic deformation of austenite at high temperatures enhances ferrite formation significantly, and consequently, the dilatation decreases markedly even at a cooling rate of 280'C/s. The created ferritic-martensitic microstructure possesses clearly lower hardness and strength than the martensitic structure. Elastic stresses cause the preferred orientation in martensite to be formed so that diametric dilatation can increase by nearly 200% under axial compression.
基金Supported by the National Key R&D Program of China under Grant No 2016YFA0401100the National Natural Science Foundation of China under Grant No 61575129the National High-Technology Research and Development Program of China under Grant No 2015AA021102
文摘In our previous study, metals have been used as absorbers in the clear plastic laser transmission welding. The effects of metal thermal conductivity on the welding quality are investigated in the present work. Four metals with distinctly different thermal conductivities, i.e., titanium, nickel, molybdenum, and copper, are selected as light absorbers. The lap welding is conducted with an 808 nm diode laser and simulation experiments are also conducted. Nickel electroplating test is carried out to minimize the side-effects from different light absorptivities of different metals. The results show that the welding with an absorber of higher thermal conductivity can accommodate higher laser input power before smoking, which produces a wider and stronger welding seam.The positive role of the higher thermal conductivity can be attributed to the fact that a desirable thermal field distribution for the molecular diffusion and entanglement is produced from the case with a high thermal conductivity.
基金supported by the National Natural Science Foundation of China (10772096)
文摘The Bauschinger and size effects in the thinfilm plasticity theory arising from the defect-energy of geometrically necessary dislocations （GNDs） are analytically investigated in this paper. Firstly, this defect-energy is deduced based on the elastic interactions of coupling dislocations （or pile-ups） moving on the closed neighboring slip plane. This energy is a quadratic function of the GNDs density, and includes an elastic interaction coefficient and an energetic length scale L. By incorporating it into the work- conjugate strain gradient plasticity theory of Gurtin, an energetic stress associated with this defect energy is obtained, which just plays the role of back stress in the kinematic hardening model. Then this back-stress hardening model is used to investigate the Bauschinger and size effects in the tension problem of single crystal Al films with passivation layers. The tension stress in the film shows a reverse dependence on the film thickness h. By comparing it with discrete-dislocation simulation results, the length scale L is determined, which is just several slip plane spacing, and accords well with our physical interpretation for the defect- energy. The Bauschinger effect after unloading is analyzed by combining this back-stress hardening model with a friction model. The effects of film thickness and pre-strain on the reversed plastic strain after unloading are quantified and qualitatively compared with experiment results.
基金financially supported by the National Natural Science Foundation of China (Nos.51773040 and 52173056)。
文摘Polymers with reversible plasticity shape memory effect(RPSME)have attracted considerable attention due to their simple programming and large deformation.However,the exact mechanisms of RPSME are still not thoroughly understood.In this work,the RPSME of SEBS/crystallizable paraffin was investigated by comparatively analyzing the performances and microstructures of samples with different paraffin content.It was found the shape fixing ratios(Rfs)of samples increased with the paraffin content,and interestingly,a significant improvement in Rf was observed when the paraffin content exceeded 60 wt%.Tensile test results showed that the deformation characteristics of samples changed from elastic to plastic as the paraffin content increased above 60 wt%.By exploring the crystallization behaviors of paraffin in various SEBS/paraffin samples,it was revealed that the microstructures of SEBS/paraffin were different when the paraffin content was below 50 wt%and above 60 wt%.In samples with low paraffin content(below 50 wt%),nearly all paraffin was co-crystallized with ethylene-co-butylene(EB)chains and its crystallization was severely restricted;while in samples with high paraffin content(above 60 wt%),“excess”paraffin appeared and this part of paraffin crystallized on the template of the EB/paraffin co-crystals,which might be responsible for the elastic-to-plastic transition and the sharp increase in Rf.Based on the above results,a possible structural model was proposed to explain the exact mechanism of RPSME in SEBS/paraffin.
基金financially supported by the National Natural Science Foundation of China (Nos.51971146,51971147,52171218 and 52271222)Shanghai Municipal Science and Technology Commission (No.21010503100)+3 种基金the Major Program for the Scientific Research Innovation Plan of Shanghai Education Commission (No.2019-01-07-00-07-E00015)Shanghai Outstanding Academic Leaders Plan,Guangxi Key Laboratory of Information Materials (Guilin University of Electronic Technology,201017-K)Shanghai Rising-Star Program (No.20QA1407100)General Program of Natural Science Foundation of Shanghai (No.20ZR1438400)。
文摘Composite solid electrolytes(CSEs) containing polymer matrices and inorganic fillers hold promise for the next generation of solid-state batteries.However,the role of residual solvents in CSEs remains controversial.This study investigated the evolution and function of the residual solvent in a polymer-Li_2B_(12)H_(12) CSE.A partial reaction occurred between Li_2B_(12)H_(12) and solvent N,N-dimethylformamide(DMF),which produced dimethylaminomethanol(DMAM) in the CSE.Density functional theory calculations have revealed that DMA M forms stronger hydrogen bonds with polyvinylidene fluoride chains than DMF,which can have a plasticizing effect on the polymer matrix,leading to lower crystallinity and quicker segment motion.Therefore,this CSE exhibited improved Li-ion conducting properties,enabling the stable cycling of Li‖LiFePO_(4) solid-state batteries.This study provided insights into the role of residual solvents in CSEs.
基金supported by the National Key Research and Development Program of China(Grant No.2018YFB0703904).
文摘A medium-carbon low-alloy steel with designed chemical composition was investigated.The steel exhibits an excellent product of strength and elongation value of 31,832 MPa%through quenching and partitioning treatment,with a tensile strength of 1413 MPa and elongation of 22%.X-ray diffraction analysis and transmission electron microscopy characterizations confirm that the retained austenite in the specimens undergoes stress-induced phase transformation to the martensite and hexagonal phases,namely the transformation-induced plasticity(TRIP)effect is triggered.This TRIP effect,triggered by the stress-induced phase transition of retained austenite,is responsible for the excellent mechanical properties obtained in the steel.For further investigating the stress-induced phase transition mechanism,thermodynamic methods are applied.Gibbs free energy of face-centered cubic-Fe,ε-Fe,ω-Fe and body-centered cubic-Fe associated with the stress-induced phase transition was calculated using molecular dynamics simulations,and a calculation method of strain energy in thermodynamic units for the stress-induced martensitic transformation is presented.The final results reveal the process and thermodynamic mechanism of stress-induced martensitic transformation in medium-carbon steels,in which the hexagonal phase can participate in the process as an intermediate product.
基金supported by the National Natural Science Foundation of China(Grant Nos.51371091,51174099,and 51001054)the Industrial Center of Jiangsu University,China(Grant No.ZXJG201586)
文摘In order to explore the dependence of plasticity of metallic material on a high magnetic held,the effects of the different magnetic induction intensities（H = 0 T,0.5 T,1 T,3 T,and 5 T） and pulses number（N = 0,10,20,30,40,and 50） on tensile strength（σ;） and elongation（δ） of 2024 aluminum alloy are investigated in the synchronous presences of a high magnetic held and external stress.The results show that the magnetic held exerts apparent and positive effects on the tensile properties of the alloy.Especially under the optimized condition of H;=1 T and N;=30,the σ;and 8 are 410 MPa and 17% that are enhanced by 9.3% and 30.8% respectively in comparison to those of the untreated sample.The synchronous increases of tensile properties are attributed to the magneto-plasticity effect on a quantum scale.That is,the magnetic held will accelerate the state conversion of radical pair generated between the dislocation and obstacles from singlet to the triplet state.The bonding energy between them is meanwhile lowered and the moving flexibility of dislocations will be enhanced.At H;= 1 T and N;= 30,the dislocation density is enhanced by 1.28 times.The relevant minimum grain size is 266.1 nm,which is reduced by 35.2%.The grain rehning is attributed to the dislocation accumulation and subsequent dynamic recrystallization.The（211） and（220） peak intensities are weakened.It is deduced that together with the recrystallization,the hne grains will transfer towards the slip plane and contribute to the slipping deformation.
基金supported by the Joint Research Center for Future Iron and Steel,SJTU&BaosteelThe author(L.M.Fu)is grateful to the financial support from Startup Fund for Youngman Research at SJTU(SFYR at SJTU,No.18X100040023).
文摘The intercritical annealing treatment at 650 and 700 ℃ results in two ultrafine-grained (UFG) dual-phase ferrite-austenitesteels. The two steels exhibit different and special discontinuous yielding and pronounced Lüders-like strain phenomenawith large yielding strain which are related to their retained γ-austenite (RA) volume fractions and RA stabilities. The steelannealed at 650 ℃ shows an absent or very small strain hardening, while the steel annealed at 700 ℃ shows an obviousstrain hardening upward curvature with increasing strain. The results show that before and during straining, the steel annealedat 650 ℃ exhibits a mixture of equiaxed and elongated UFG α-ferrite and austenite phases;however, the steel annealed at700 ℃ exhibits only elongated UFG α and γ phases. It was found that most of the γ-austenite to α′-martensite transformationoccurred at the initial deformation stage and very small or almost no transformation occurred afterward. This demonstratesthat the strain-induced martensite (SIM) transformation (γ-α′) or transformation-induced plasticity (TRIP) effect dominatesonly at the initial deformation stage. RA remained stable, and no TRIP effect was observed at the final deformation stage. Theload-unload-reload test was performed to evaluate the back stress (σb) hardening effect. It is believed that the pronouncedstrain hardening behavior at the later deformation stage is mainly associated with σb enhancement induced by the strainpartitioning between the soft and hard phases due to SIM transformation during tensile deformation.
基金supported by the Shanghai Municipal Natural Science Foundation(Grant No.17ZR1410400)the Shanghai Municipal Science and Technology Commission(Grant Nos.15DZ2260300,15DZ2260301)
文摘The microstructures and mechanical properties of ferrite-based lightweight steel with different compositions were investigated by tensile test,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray diffraction（XRD）and thermodynamic calculation（TC）.It was shown that the ferrite-based lightweight steels with 5wt.%or 8wt.%Al were basically composed of ferrite,austenite andκ-carbide.As the annealing temperature increased,the content of the austenite in the steel gradually increased,while theκ-carbide gradually decomposed and finally disappeared.The mechanical properties of the steel with 5wt.%Al and 2wt.%Cr,composed of ferrite and Cr7C3carbide at different annealing temperatures,were significantly inferior to those of others.The steel containing 5wt.%Al,annealed at 820°C for 50sthen rapidly cooled to 400°C and held for 180s,can obtain the best product of strength and elongation（PSE）of 31242MPa·%.The austenite stability of the steel is better,and its PSE is higher.In addition,the steel with higher PSE has a more stable instantaneous strain hardening exponent（n value）,which is mainly caused by the effect of transformation induced plasticity（TRIP）.When theκ-carbide or Cr7C3carbide existed in the microstructure of the steel,there was an obvious yield plateau in the tensile curve,while its PSE decreased significantly.
基金National Key R&D Program of China,Grant/Award Number:2018YFC1504901Science and technology program of Gansu Province,Grant/Award Numbers:21JR7RA738,21JR7RA739+1 种基金Science and Technology Development Project of China Railway Research Institute Co.Ltd,Grant/Award Number:2017‐KJ008‐Z008‐XBNatural Science Foundation of Gansu Province,Grant/Award Number:145RJZA068。
文摘To explore the cumulative deformation effect of the dynamic response of a tunnel crossing the hauling sliding surface under earthquakes,the shaking table test was conducted in this study.Combined with the numerical calculations,this study proposed magnification of the Arias intensity(MIa)to characterize the overall local deformation damage of the tunnel lining in terms of the deformation characteristics,frequency domain,and energy.Using the time‐domain analysis method,the plastic effect coefficient(PEC)was proposed to characterize the degree of plastic deformation,and the applicability of the seismic cumulative failure effect(SCFE)was discussed.The results show that the low‐frequency component(f1 and f2≤10 Hz)and the high‐frequency component(f3 and f4>10 Hz)acceleration mainly cause global and local deformation of the tunnel lining.The local deformation caused by the high‐frequency wave has an important effect on the seismic damage of the lining.The physical meaning of PEC is more clearly defined than that of the residual strain,and the SCFE of the tunnel lining can also be defined.The SCFE of the tunnel lining includes the elastic deformation effect stage(<0.15g),the elastic–plastic deformation effect stage(0.15g–0.30g),and the plastic deformation effect stage(0.30g–0.40g).This study can provide valuable theoretical and technical support for the construction of traffic tunnels in high‐intensity earthquake areas.
基金supported by the National Natural Science Foundation of China (Grant no. 11472262)the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant no. XDB22040502)+1 种基金the Collaborative Innovation Center of Suzhou Nano Science and Technologythe Fundamental Research Funds for the Central Universities
文摘Development of high-performance phase transformation electrodes in lithium ion batteries requires comprehensive studies on stress-mediated lithiation involving migration of the phase interface. It brings out many counter-intuitive phenomena, especially in nanoscale electrodes, such as the slowing down migration of phase interface, the vanishing of miscibility gap under high charge rate, and the formation of surface crack during lithiation. However, it is still a challenge to simulate the evolution of stress in arbitrarily-shaped nanoscale electrodes, accompanied with phase transformation and concurrent plastic deformation. This article gives a brief review of our efforts devoted to address these issues by developing phase field model and simulation. We demonstrate that the miscibility gap of two-phase state is affected not only by stress but also by surface reaction rate and particle size. In addition, the migration of phase interface slows down due to stress. It reveals that the plastic deformation generates large radial expansion, which is responsible for the transition from surface hoop compression to surface hoop tension that may induce surface crack during lithiation. We hope our effort can make a contribution to the understanding of stress-coupled kinetics in phase transformation electrodes.
基金support from the Steel Joint Funds of the National Natural Science Foundation of China(Grant No.U1560204)Research Grants Council of Hong Kong(Grant Nos.HKU719712E,HKU712713E)Small Project Funding of HKU(Grant No.201409176053)
文摘The Luders deformation behavior in a medium Mn transformation induced plasticity （TRIP） steel is investigated at different temperatures ranging from 25 to 300 ℃. It demonstrates that the Ltiders band appears at all testing temperatures but with varied Luders strains which do not change monoton ically with temperature. The martensitic transformation is simultaneously observed within the Ltiders band in varying degrees depending on the testing temperature. It is well verified that the martensitic transformation is not responsible for the formation of Luders band, and a reasonable explanation is given for the non-monotonic variation of Luders strain with increasing temperature.
基金financial support from the National Natural Science Foundation of China (Grant No. 50904004)
文摘As metallic foams used for energy absorption in the automotive and aerospace industries, recently invented lotus-type porous metals are viewed as potential energy absorbers. Yet, solid conclusion on their eligibility as energy absorbers is still in question, particularly when compression is in the direction perpendicular to the axial orientation of cylindrical pores. In this work, the energy absorption of lotus-type porous coppers in the perpendicular direction is investigated at strain rates from 0.001 s^（-1） to^2400 s^（-1）. The energy absorption capacity and the energy absorption efficiency are calculated to be4–16 k J/kg and 0.32–0.7, respectively, slightly inferior to metal foams and the same porous solid compressed in the parallel direction due to the shortened extent of the plateau stress region. The deformation mechanism is examined experimentally in conjunction with finite element modeling. Both suggest that gradual squeeze and collapse of pores are the mechanisms accommodating the energy absorption. The deformation is generally evenly distributed over pore ligaments and independent of strain rate.
文摘In the present study, films and coatings for food applications based on a gum exudate from Brea tree （Cercidium praecox） were formulated and the influence of plasticizer content on their functional properties was evaluated. Brea gum is a renewable resource available in semi-desert areas, extracted by native people. Films were produced by casting method and characterized through water vapour permeability, mechanical （tensile strength and elongation at break）, morphological and optical properties. Glycerol was used as plasticizer. Brea gum films presented good visual aspect, transparency and amber colour. Microscopic observation showed a dense and homogeneous structure. Film wettability increased with glycerol content due to hydrophilic nature of the plasticizer. Solubility of films in water increased with temperature. Water sorption isotherms of films at 25 ~C showed that at high aw （above 0.50）, the film matrix swells altering its structure and properties. Water vapour permeability remained practically constant up to 20% of glycerol content and then increases linearly with the plasticizer. The addition of glycerol decreased the opacity and tensile strength. The best film properties were obtained at 20% of glycerol concentration.
基金financially supported by the Fundamental Research Funds for the Central Universities (No. 2020MS058)。
文摘We introduce a non-equiatomic Fe_(61)Mn_(18)Si_(11)Cr_(10) medium entropy alloy designed by subjecting it to transformation-induced plasticity upon deformation at room temperature. Microstructure characterization carried out using scanning electron microscopy(SEM), electron backscatter diffraction(EBSD), transmission electron microscopy(TEM) and X-ray diffraction(XRD) shows a homogeneous solid solution FCC + BCC structured dual phase. Investigations on the deformation substructures at specific strain levels via EBSD reveal the deformation-induced transformations of γ→α′ and γ→ ε. The strengths, particularly yield strength, of the designed alloy are found to be higher than these of the well-studied five component FeMnNiCoCr system for the introduction of the hard phase( α′-martensite). When tensile tests are performed at different strain rates of 10^(–4)s^(-1), 10^(–3)s^(-1), 10^(–2)s^(-1), the tested material exhibits a slightly negative strain rate sensitivity and work hardening rate sensitivity.
文摘In the present study,the performance of reinforced concrete tunnel(RCT)under internal water pressure is evaluated by using nonlinear finite element analysis and surrogate models.Several parameters,including the compressive and tensile strength of concrete,the size of the longitudinal reinforcement bar,the transverse bar diameter,and the internal water pre ssure,are considered as the input variables.Based on the levels of variables,36 mix designs are selected by the Taguchi method,and 12 mix designs are proposed in this study.Carbon fiber reinforced concrete(CFRC)or glass fiber reinforced concrete(GFRC)is considered for simulating these 12 samples.Principal component regression(PCR),Multi Ln equation regression(MLnER),and gene expression programming(GEP)are employed for predicting the percentage of damaged surfaces(PDS)of the RCT,the effective tensile plastic strain(ETPS),the maximum deflection of the RCT,and the deflection of crown of RCT.The error terms and statistical parameters,including the maximum positive and negative errors,mean absolute percentage error(MAPE),root mean square error(RMSE),coefficient of determination,and normalized square error(NMSE),are utili zed to evaluate the accuracy of the models.Based on the results,GEP performs better than other models in predicting the outputs.The results sh ow that the internal water pressure and the mechanical properties of concrete have the most effect on the damag e and deflection of the RCT.
