Shaping effects of the E-fishbone in tokamaks are investigated. Coordinates related to the Solov＇ev configuration are used to calculate the precession frequency and kinetic contribu- tion. It is shown that elongation...Shaping effects of the E-fishbone in tokamaks are investigated. Coordinates related to the Solov＇ev configuration are used to calculate the precession frequency and kinetic contribu- tion. It is shown that elongation does not change the precession frequency and the kinetic energy. Growth rates of the E-fishbone vary with elongation which essentially has destabilizing effects. For elongated tokamaks, triangularity has a stabilizing effect on the modes which play a compensative role. The results may apply to Sunist.展开更多
The size and shape effect(SSE)of components has become a critical issue for mechanical properties,application reliability,and processing.In this study,the creep rupture life(CRL)of components with different wall thick...The size and shape effect(SSE)of components has become a critical issue for mechanical properties,application reliability,and processing.In this study,the creep rupture life(CRL)of components with different wall thicknesses and positions in a combustion chamber casing simulator made of K439B superalloy was investigated.The intrinsic mechanisms of the SSE were explored from the dendrite structure,volume fraction and size of theγ'phase,and element segregation,etc.It is shown that this casting exhibits a strong SSE of creep rupture life,characterized by a significant difference in the CRL values up to 60%with the variation of wall thickness and position in the casing.In terms of casting technology,the influence of SSE on CRL is actually determined by the cooling rate.The SSE on the creep rupture life originates from the dendrite structure(such as the secondary dendrite arm spacing),volume fraction size of theγ'phase in the dendrite trunk,and elements segregation rate.This work may have implications for the design and application of engineering components with large sizes and complex structures.展开更多
The emergence of additive manufacturing technology,particularly laser powder bed fusion,has revitalized NiTi alloy production.However,challenges arise regarding its mechanical properties and diminishing shape memory e...The emergence of additive manufacturing technology,particularly laser powder bed fusion,has revitalized NiTi alloy production.However,challenges arise regarding its mechanical properties and diminishing shape memory effect,which hinder its widespread application.Heat treatment has been identified as a method to enhance the performance of metallic materials in the realm of additive manufacturing.This process eliminates residual stress and enhances performance through precipitation strengthening.This study conducted a comprehensive annealing investigation on NiTi alloys to explore the impact of annealing time and temperature on the phase transformation behavior and shape memory performance.The mechanism underlying the performance enhancement was analyzed using scanning electron microscopy,energy-dispersive X-ray spectroscopy,electron backscatter diffraction,and transmission electron microscopy.The findings revealed that different annealing conditions resulted in multistep phase transformation behavior,with the 500℃-5 h sample exhibiting the best mechanical properties owing to the formation of nanoscale dispersed precipitates like Ni_(4)Ti_(3).However,higher temperatures led to larger precipitates,significantly weakening the properties of the NiTi alloy.Additionally,the annealing treatment did not have a notable impact on the grain size,texture strength,or direction.This study provides valuable insights for optimizing the heat treatment process of LPBF-NiTi alloys.展开更多
The experimental study in this paper focuses on the effects of the layer orientation and sample shape on failure strength and fracture pattern of samples tested under Brazilian test conditions(i.e.diametrical loading ...The experimental study in this paper focuses on the effects of the layer orientation and sample shape on failure strength and fracture pattern of samples tested under Brazilian test conditions(i.e.diametrical loading of cylindrical discs)for one particular layered sandstone which is from Modave in the south of Belgium.The variations of the strength in combination with the failure patterns are examined as a function of the inclination angle between the layer plane and the loading direction.The experimental,results clearly show that the induced fracture patterns are a combination of tensile and/or shear fractures.In shape effect experiments the layer thickness and the number of layer boundaries are investigated.Different blocks of Modave sandstone are used to prepare samples.The layer thickness is different among the various blocks,but the layer thickness in each studied rock block can be considered to be constant;hence,the number of layer boundaries changes according to the sample diameter for samples of the same block.The experimental study shows that the layer thickness plays a more important role than the number of layer boundaries per sample.展开更多
Isolated pillars in underground mines are subjected to uniaxial stress,and the load bearing cross-section of pillars is commonly rectangularly shaped.In addition,the uniaxial compression test(UCT)is widely used for de...Isolated pillars in underground mines are subjected to uniaxial stress,and the load bearing cross-section of pillars is commonly rectangularly shaped.In addition,the uniaxial compression test(UCT)is widely used for determining the basic mechanical properties of rocks and revealing the mechanism of isolated pillar disasters under unidimensional stress.The shape effects of rock mechanical properties under uniaxial compression are mainly quantitatively reflected in the specific shape ratios of rocks.Therefore,it is necessary to study the detailed shape ratio effects on the mechanical properties of rectangular prism rock specimens and isolated pillars under uniaxial compressive stress.In this study,granite,marble and sandstone rectangular prism specimens with various height to width ratios(r)and width to thickness ratios(u)were prepared and tested.The study results show that r and u have a great influence on the bearing ability of rocks,and thin or high rocks have lower uniaxial compressive strength.Reducing the level of r can enhance the u effect on the strength of rocks,and increasing the level of u can enhance the r effect on the strength of rocks.The lateral strain on the thickness side of the rock specimen is larger than that on the width side,which implies that crack growth occurs easily on the thickness side.Considering r and u,a novel strength prediction model of isolated pillars was proposed based on the testing results,and the prediction model was used for the safety assessment of 179 isolated pillars in the Xianglu Mountain Tungsten Mine.展开更多
An anomalous isotope effect exists in many heavy element isotope systems （e.g., Sr, Gd, Zn, U）. This effect used to be called the ＂odd--even isotope effect＂ because the odd mass number isotopes behave differently ...An anomalous isotope effect exists in many heavy element isotope systems （e.g., Sr, Gd, Zn, U）. This effect used to be called the ＂odd--even isotope effect＂ because the odd mass number isotopes behave differently from the even mass number isotopes. This mass-indepen- dent isotope fractionation driving force, which originates from the difference in the ground-state electronic energies caused by differences in nuclear size and shape, is cur- rently denoted as the nuclear field shift effect （NFSE）. It is found that the NFSE can drive isotope fractionation of some heavy elements （e.g., Hg, T1, U） to an astonishing degree, far more than the magnitude caused by the con- ventional mass-dependent effect （MDE）. For light ele- ments, the MDE is the dominant factor in isotope fractionation, while the NFSE is neglectable. Furthermore, the MDE and the NFSE both decrease as temperatures increase, though at different rates. The MDE decreases rapidly with a factor of 1/T2, while the NFSE decreases slowly with a factor of 1/T. As a result, even at high temperatures, the NFSE is still significant for many heavy element isotope systems. In this review paper, we begin with an introduction of the basic concept of the NSFE, including its history and recent progress, and follow with the potential implications of the inclusion of the NFSE into the kinetic isotope fractionation effect （KIE） and heavy isotope geochronology.展开更多
Laser additive manufacturing (AM) of lattice structures with light weight, excellent impact resistance, and energy absorption performance is receiving considerable attention in aerospace, transportation, and mechanica...Laser additive manufacturing (AM) of lattice structures with light weight, excellent impact resistance, and energy absorption performance is receiving considerable attention in aerospace, transportation, and mechanical equipment application fields. In this study, we designed four gradient lattice structures (GLSs) using the topology optimization method, including the unidirectional GLS, the bi-directional increasing GLS, the bi-directional decreasing GLS and the none-GLS. All GLSs were manufactureed by laser powder bed fusion (LPBF). The uniaxial compression tests and finite element analysis were conducted to investigate the influence of gradient distribution features on deformation modes and energy absorption performance of GLSs. The results showed that, compared with the 45° shear fracture characteristic of the none-GLS, the unidirectional GLS, the bi-directional increasing GLS and the bi-directional decreasing GLS had the characteristics of the layer-by-layer fracture, showing considerably improved energy absorption capacity. The bi-directional increasing GLS showed a unique combination of shear fracture and layer-by-layer fracture, having the optimal energy absorption performance with energy absorption and specific energy absorption of 235.6 J and 9.5 J g-1 at 0.5 strain, respectively. Combined with the shape memory effect of NiTi alloy, multiple compression-heat recovery experiments were carried out to verify the shape memory function of LPBF-processed NiTi GLSs. These findings have potential value for the future design of GLSs and the realization of shape memory function of NiTi components through laser AM.展开更多
SMPU （shape memory polyurethane） non-ionomers and ionomers, synthesized with poly（c-caprolactone） （PCL）, 4, 4＇-diphenylmethane diisocyanate （MDI）, 1,4-butanediol （BDO）, dimethylolpropionic acid （DMPA） wer...SMPU （shape memory polyurethane） non-ionomers and ionomers, synthesized with poly（c-caprolactone） （PCL）, 4, 4＇-diphenylmethane diisocyanate （MDI）, 1,4-butanediol （BDO）, dimethylolpropionic acid （DMPA） were measured with cyclic tensile test and strain recovery test. The relations between the structure and shape memory effect of these two series were studied with respect to the ionic group content and the effect of neutralization. The resulting data indicate that, with the introduction of asymmetrical extender, the stress at 100% elongation is decreased for PU non-ionomer and ionomer series, especially lowered sharply for non-ionomer series; the fixation ratio of ionomer series is not affected obviously by the ionic group content; the total recovery ratio of ionomer series is decreased greatly. After sufficient relaxation time for samples stretched beforehand, the switching temperature is raised slightly, whereas the recovery ratio measured with strain recovery test method is lowered with increased DMPA content. The characterization with FT-IR, DSC, DMA elucidated that, the ordered hard domain of the two series is disrupted with the introduction of DMPA which causes more hard segments to dissolve in soft phase; ionic groups on hard segment enhance the cohesion between hard segments especially at high ionic group content and significantly facilitate the phase separation compared with the corresponding non-ionomer at moderate ionic group content.展开更多
A macroscopic based multi-mechanism constitutive model is constructed in the framework of irreversible thermodynamics to describe the degeneration of shape memory effect occurring in the thermo-mechanical cyclic defor...A macroscopic based multi-mechanism constitutive model is constructed in the framework of irreversible thermodynamics to describe the degeneration of shape memory effect occurring in the thermo-mechanical cyclic deformation of NiTi shape memory alloys (SMAs). Three phases, austenite A, twinned martensite and detwinned martensite , as well as the phase transitions occurring between each pair of phases (, , , , and are considered in the proposed model. Meanwhile, two kinds of inelastic deformation mechanisms, martensite transformation-induced plasticity and reorientation-induced plasticity, are used to explain the degeneration of shape memory effects of NiTi SMAs. The evolution equations of internal variables are proposed by attributing the degeneration of shape memory effect to the interaction between the three phases (A, , and and plastic deformation. Finally, the capability of the proposed model is verified by comparing the predictions with the experimental results of NiTi SMAs. It is shown that the degeneration of shape memory effect and its dependence on the loading level can be reasonably described by the proposed model.展开更多
Shape memory polymers(SMPs)usually have a one-way shape memory effect.In this paper,an easy-operating method to realize a two-way shape memory effect was demonstrated in a ring-shaped bilayer structure where the two l...Shape memory polymers(SMPs)usually have a one-way shape memory effect.In this paper,an easy-operating method to realize a two-way shape memory effect was demonstrated in a ring-shaped bilayer structure where the two layers are SMPs with different thermal transition temperatures.By designing specific thermomechanical processes,the mismatched deformation between the two layers leads to a morphology change of ring-shaped bilayer structures from a smooth ring to a gear-like buckling shape under cooling and a reversible recovery to the smooth shape under heating.Such a morphology change is ascribed to occurrence and recovery of thermoelastic buckling.This method was validated by finite element simulation.We experimentally investigated the influence of pre-strain on buckling,and it was found that both the buckling occurrence and recovery temperature vary with pre-strain.Furthermore,considering a ring-shaped SMP-SMP bilayer structure,finite element analysis was conducted to study the influence of film thickness and modulus ratio of two layers on buckling behavior.The results showed that the critical buckling wavelength was greatly influenced by film thickness and modulus ratio.W e made a theoretical analysis that accorded well with the numerical results.展开更多
An intrinsic two-way shape memory effect with a fully recoverable strain of 1.0%was achieved in an as-prepared Ni50Mn37.5Sn12.5 metamagnetic shape memory microwire fabricated by Taylor-Ulitovsky method.This two-way sh...An intrinsic two-way shape memory effect with a fully recoverable strain of 1.0%was achieved in an as-prepared Ni50Mn37.5Sn12.5 metamagnetic shape memory microwire fabricated by Taylor-Ulitovsky method.This two-way shape memory effect is mainly owing to the internal stress caused by the retained martensite in austenite matrix,as revealed by transmission electron microscopy observations and highenergy X-ray diffraction experiments.After superelastic training for 30 loading/unloading cycles at room temperature,the amount of retained martensite increased and the recoverable strain of two-way shape memory effect increased significantly to 2.2%.Furthermore,a giant recoverable strain of 11.2%was attained under a bias stress of 300 MPa in the trained microwire.These properties confer this microwire great potential for micro-actuation applications.展开更多
With the development of radioactive-ion-beam facilities,many exotic phenomena have been discovered or predicted in the nuclei far from the stability line,including cluster structure,shell structure,deformed halo,and s...With the development of radioactive-ion-beam facilities,many exotic phenomena have been discovered or predicted in the nuclei far from the stability line,including cluster structure,shell structure,deformed halo,and shape decoupling effects.The study of exotic nuclear phenomena is at the frontier of nuclear physics nowadays.The covariant density functional theory(CDFT)is one of the most successful microscopic models in describing the structure of nuclei in almost the whole nuclear chart.Within the framework of CDFT,toward a proper treatment of deformation and weak binding,the deformed relativistic Hartree-Bogoliubov theory in continuum(DRHBc)has been developed.In this contribution,we review the applications and extensions of the DRHBc theory to the study of exotic nuclei.The DRHBc theory has been used to investigate the deformed halos in B,C,Ne,Na,and Mg isotopes and the theoretical descriptions are reasonably consistent with available data.A DRHBc Mass Table Collaboration has been founded,aiming at a high precision nuclear mass table with deformation and continuum effects included,which is underway.By implementing the angular momentum projection based on the DRHBc theory,the rotational excitations of deformed halos have been investigated and it is shown that the deformed halos and shape decoupling effects also exist in the low-lying rotational excitation states of deformed halo nuclei.展开更多
The influence of aging on the microstructure and mechanical properties of Cu-11.6wt%Al-3.9wt%Ni-2.5wt%Mn shape memory alloy（SMA） was studied by means of scanning electron microscopy（SEM）,transmission electron micr...The influence of aging on the microstructure and mechanical properties of Cu-11.6wt%Al-3.9wt%Ni-2.5wt%Mn shape memory alloy（SMA） was studied by means of scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray diffractometer,and differential scanning calorimeter（DSC）.Experimental results show that bainite,γ2,and α phase precipitates occur with the aging effect in the alloy.After aging at 300°C,the bainitic precipitates appear at the early stages of aging,while the precipitates of γ2 phase are observed for a longer aging time.When the aging temperature increases,the bainite gradually evolves into γ2 phase and equilibrium α phase（bcc） precipitates from the remaining parent phase.Thus,the bainite,γ2,and α phases appear,while the martensite phase disappears progressively in the alloy.The bainitic precipitates decrease the reverse transformation temperature while the γ2 phase precipitates increase these temperatures with a decrease of solute content in the retained parent phase.On the other hand,these precipitations cause an increasing in hardness of the alloy.展开更多
A NiTi shape memory alloy （SMA） modified by Ta ion implantation was subjected to oxidation treatment in air at 723 and 873 K. Atomic force microscopy （AFM）, Auger electron spectroscopy （AES）, and grazing inciden...A NiTi shape memory alloy （SMA） modified by Ta ion implantation was subjected to oxidation treatment in air at 723 and 873 K. Atomic force microscopy （AFM）, Auger electron spectroscopy （AES）, and grazing incidence X-ray diffraction （GIXRD） measurements were conducted to investigate the surface characteristics, including surface topography, elemental depth profiles, and surface phase structures. The surface roughness of the Ta-implanted NiTi increases after oxidation, and the higher the oxidation temperature is, the larger the value is. The surface of the Ta-implanted NiTi oxidized at 723 K is a nanolayer mainly composed of TiO2/Ta2O5 and TiO with depressed Ni content. The Ta-implanted NiTi oxidized at 873 K is mainly covered by rutile TiO2 in several micrometers of thickness. Potentiodynamic polarization tests indicated that the corrosion resistance of the Ta-implanted NiTi was improved after thermal oxidation at 723 K, but a negative impact was found for the Ta-implanted NiTi oxidized at 873 K.展开更多
Improvement of shape, memory effect (SME) in Fe-Mn-Si based alloys has been investigated, compared with that by conventional 'training' treatment. It is found that SME in Fe-Mn-Si alloy can be greatly improved...Improvement of shape, memory effect (SME) in Fe-Mn-Si based alloys has been investigated, compared with that by conventional 'training' treatment. It is found that SME in Fe-Mn-Si alloy can be greatly improved by ausforming and 3.8%recovery strain and 2.2% complete recovery strain can be reached by ausforming at 973 K when dynamic recrystallization has just occurred. The mechanism for the improvement of SME is proposed.展开更多
The microstructure,phase transformation,compression property and strain recovery characteristics of equiatomic Ru-Nb high temperature shape memory alloy were investigated by means of optical microscope,X-ray diffracti...The microstructure,phase transformation,compression property and strain recovery characteristics of equiatomic Ru-Nb high temperature shape memory alloy were investigated by means of optical microscope,X-ray diffraction(XRD),differential scanning calorimetry(DSC),compression tests and transmission electron microscopy(TEM).When cooling the alloy specimen from high temperature to room temperature,β(parent phase)→β’(interphase)→β″(martensite) two step phase transformation occurs.The microstructure at room temperature shows regularly arranged band morphology with the monoclinic crystal structure.The twinning relationship between the martensite bands was determined to be(101) Type I.Reorientation and of the martensite bands inside the variant and dislocation were found during compression at room temperature.The maximum complete recovery strain is about 1.5%.展开更多
The effects of 1 Me V electron irradiation in air at a fixed accumulated dose and dose rates of 393.8,196.9,78.8,and 39.4 Gy s^(-1)on a shape memory epoxy(SMEP)resin were studied.Under low-dose-rate irradiation,accele...The effects of 1 Me V electron irradiation in air at a fixed accumulated dose and dose rates of 393.8,196.9,78.8,and 39.4 Gy s^(-1)on a shape memory epoxy(SMEP)resin were studied.Under low-dose-rate irradiation,accelerated degradation of the shape memory performance was observed;specifically,the shape recovery ratio decreased exponentially with increasing irradiation time(that is,with decreasing dose rate).In addition,the glass transition temperature of the SMEP,as measured by dynamic mechanical analysis,decreased overall with decreasing dose rate.The dose rate effects of 1 Me V electron irradiation on the SMEP were confirmed by structural analysis using electron paramagnetic resonance(EPR)spectroscopy and Fourier transform infrared(FTIR)spectroscopy.The EPR spectra showed that the concentration of free radicals increased exponentially with increasing irradiation time.Moreover,the FTIR spectra showed higher intensities of the peaks at 1660 and 1720 cm^(-1),which are attributed to stretching vibrations of amide C=O and ketone/acid C=O,at lower dose rates.The intensities of the IR peaks at 1660 and 1720 cm^(-1) increased exponentially with increasing irradiation time,and the relative intensity of the IR peak at 2926 cm^(-1)decreased exponentially with increasing irradiation time.The solid-state13 C nuclear magnetic resonance(NMR)spectra of the SMEP before and after 1 Me V electron irradiation at a dose of 1970 k Gy and a dose rate of 78.8 Gy s^(-1) indicated damage to the CH_(2)–N groups and aliphatic isopropanol segment.This result is consistent with the detection of nitrogenous free radicals,a phenoxy-type free radical,and several types of pyrolytic carbon radicals by EPR.During the subsequent propagation process,the free radicals produced at lower dose rates were more likely to react with oxygen,which was present at higher concentrations,and form the more destructive peroxy free radicals and oxidation products such as acids,amides,and ketones.The increase in peroxy free radicals at lower dose rates was thought to accelerate the degradation of the macroscopic performance of the SMEP.展开更多
A two-way shape memory effect (TWSM E) in the Ti46.3Ni44.7Nb9 alloy has been systematically investigated by means of bending test and transmission electron microscopy (TEM ) observations. Based on the analysis of the ...A two-way shape memory effect (TWSM E) in the Ti46.3Ni44.7Nb9 alloy has been systematically investigated by means of bending test and transmission electron microscopy (TEM ) observations. Based on the analysis of the microstructure after training. the mechanism of TWSME in the Ti46.3 Ni44.7Nb9 alloy has been discussed.展开更多
Natural diatomite （DT） is the ancient deposit of diatom skeleton with many regular pores of 50-200 nm and also an abundant source of biogenic silica. Although silica is considered biologically safe and there is an i...Natural diatomite （DT） is the ancient deposit of diatom skeleton with many regular pores of 50-200 nm and also an abundant source of biogenic silica. Although silica is considered biologically safe and there is an increasing interest of using natural diatomite for biomedical applications, the toxicity information about natural diatomite is still missing. Here, cytotoxicity of natural diatomite on osteoblasts and fibroblasts were compared to hydroxyapatite and the relationships between cytotoxicity and diatomite sizes, dose, geometry or impurity were systematically investigated. Cell adhesion and interaction with diatomite particles were also fluorescently observed, The results clearly suggested a size-, dose- and shape-dependent cytotoxicity of natural diatomite. Disk-shaped diatomite particles with average size of 30μm in diameter revealed the least toxicity, while the diatomite particles with irregular shapes and sizes less than 10 μm were remarkably toxic. Diatomite particles with proper sizes were then selected to investigate the reinforcing effect on injectable calcium phosphate bone cement. Results showed that diatomite significantly improved the compressive strength of bone cement but did not alter the injectability of the cement, This work provided important biocompatibility information of natural diatomite and demonstrated the feasibility of using selected diatomite as bone implant material.展开更多
The Effect of the thermal cycling training under constant strain on the two-way shape memory effect (TWSME) in a Ti36l\li49Hf15 high temperature shape memory alloy (SMA) has been investigated by bending tests. The res...The Effect of the thermal cycling training under constant strain on the two-way shape memory effect (TWSME) in a Ti36l\li49Hf15 high temperature shape memory alloy (SMA) has been investigated by bending tests. The results indicated that the training procedure is beneficial to get the better TWSME. The two-way shape memory strain increases with increasing the training strain. And it decreases with increasing the training temperature. The TWSME obtained in the present alloy shows poorer stability compared with that obtained in the TiNi alloys.展开更多
基金supported by National Natural Science Foundation of China (Nos. 11261140327, 11005035, 11175058)National Magnetic Confinement Fusion Science Program of China (No. 2009GB105002)
文摘Shaping effects of the E-fishbone in tokamaks are investigated. Coordinates related to the Solov＇ev configuration are used to calculate the precession frequency and kinetic contribu- tion. It is shown that elongation does not change the precession frequency and the kinetic energy. Growth rates of the E-fishbone vary with elongation which essentially has destabilizing effects. For elongated tokamaks, triangularity has a stabilizing effect on the modes which play a compensative role. The results may apply to Sunist.
基金financially supported by the National Science and Technology Major Project of China (No.J2019-VI-0004-0117)a Laboratory Fund Project (6142903220101)。
文摘The size and shape effect(SSE)of components has become a critical issue for mechanical properties,application reliability,and processing.In this study,the creep rupture life(CRL)of components with different wall thicknesses and positions in a combustion chamber casing simulator made of K439B superalloy was investigated.The intrinsic mechanisms of the SSE were explored from the dendrite structure,volume fraction and size of theγ'phase,and element segregation,etc.It is shown that this casting exhibits a strong SSE of creep rupture life,characterized by a significant difference in the CRL values up to 60%with the variation of wall thickness and position in the casing.In terms of casting technology,the influence of SSE on CRL is actually determined by the cooling rate.The SSE on the creep rupture life originates from the dendrite structure(such as the secondary dendrite arm spacing),volume fraction size of theγ'phase in the dendrite trunk,and elements segregation rate.This work may have implications for the design and application of engineering components with large sizes and complex structures.
基金supported by National Key R&D Program of China(Grant No.2022YFB4601701)74th Batch of General Funding from the China Postdoctoral Science Foundation(Grant No.2023M741341)+7 种基金5th Batch of Special Grants from the China Postdoctoral Science Foundation(before the station,Grant No.2023TQ0129)Postdoctoral Fellowship Program of CPSF(Grant No.GZB20230257)National Natural Science Foundation of China(Grant Nos.52375289,52205310)Natural Science Foundation of Shandong Province(Grant No.ZR2021QE263)Science and Technology Development Program of Jilin Province(Grant No.20230508045RC)Capital Construction Fund plan within the budget of Jilin Province(Grant No.2023C041-4)Chongqing Natural Science Foundation(Grant No.CSTB2022NSCQ-MSX0225)the Shandong Postdoctoral Science Foundation(Grant No.SDCX-ZG-202400238).
文摘The emergence of additive manufacturing technology,particularly laser powder bed fusion,has revitalized NiTi alloy production.However,challenges arise regarding its mechanical properties and diminishing shape memory effect,which hinder its widespread application.Heat treatment has been identified as a method to enhance the performance of metallic materials in the realm of additive manufacturing.This process eliminates residual stress and enhances performance through precipitation strengthening.This study conducted a comprehensive annealing investigation on NiTi alloys to explore the impact of annealing time and temperature on the phase transformation behavior and shape memory performance.The mechanism underlying the performance enhancement was analyzed using scanning electron microscopy,energy-dispersive X-ray spectroscopy,electron backscatter diffraction,and transmission electron microscopy.The findings revealed that different annealing conditions resulted in multistep phase transformation behavior,with the 500℃-5 h sample exhibiting the best mechanical properties owing to the formation of nanoscale dispersed precipitates like Ni_(4)Ti_(3).However,higher temperatures led to larger precipitates,significantly weakening the properties of the NiTi alloy.Additionally,the annealing treatment did not have a notable impact on the grain size,texture strength,or direction.This study provides valuable insights for optimizing the heat treatment process of LPBF-NiTi alloys.
基金The fnancial support of the Research Council of the Katholieke Universiteit Leuven(OT-project OT/03/35)
文摘The experimental study in this paper focuses on the effects of the layer orientation and sample shape on failure strength and fracture pattern of samples tested under Brazilian test conditions(i.e.diametrical loading of cylindrical discs)for one particular layered sandstone which is from Modave in the south of Belgium.The variations of the strength in combination with the failure patterns are examined as a function of the inclination angle between the layer plane and the loading direction.The experimental,results clearly show that the induced fracture patterns are a combination of tensile and/or shear fractures.In shape effect experiments the layer thickness and the number of layer boundaries are investigated.Different blocks of Modave sandstone are used to prepare samples.The layer thickness is different among the various blocks,but the layer thickness in each studied rock block can be considered to be constant;hence,the number of layer boundaries changes according to the sample diameter for samples of the same block.The experimental study shows that the layer thickness plays a more important role than the number of layer boundaries per sample.
基金funded by the National Natural Science Foundation of China(Nos.51774326,42177164,41807259,and41702350)Hunan Young Talent(No.2021RC3007)+2 种基金the open fund of Mining Disaster Prevention and Control Ministry Key Laboratory at Shandong University of Science and Technology(No.MDPC201917)the Fundamental Research Funds for the Central Universities of Central South University(No.2019zzts668)the Innovation-Driven Project of Central South University(No.2020CX040)。
文摘Isolated pillars in underground mines are subjected to uniaxial stress,and the load bearing cross-section of pillars is commonly rectangularly shaped.In addition,the uniaxial compression test(UCT)is widely used for determining the basic mechanical properties of rocks and revealing the mechanism of isolated pillar disasters under unidimensional stress.The shape effects of rock mechanical properties under uniaxial compression are mainly quantitatively reflected in the specific shape ratios of rocks.Therefore,it is necessary to study the detailed shape ratio effects on the mechanical properties of rectangular prism rock specimens and isolated pillars under uniaxial compressive stress.In this study,granite,marble and sandstone rectangular prism specimens with various height to width ratios(r)and width to thickness ratios(u)were prepared and tested.The study results show that r and u have a great influence on the bearing ability of rocks,and thin or high rocks have lower uniaxial compressive strength.Reducing the level of r can enhance the u effect on the strength of rocks,and increasing the level of u can enhance the r effect on the strength of rocks.The lateral strain on the thickness side of the rock specimen is larger than that on the width side,which implies that crack growth occurs easily on the thickness side.Considering r and u,a novel strength prediction model of isolated pillars was proposed based on the testing results,and the prediction model was used for the safety assessment of 179 isolated pillars in the Xianglu Mountain Tungsten Mine.
基金funding support from the973 Program(2014CB440904)Chinese NSF projects(41225012,41490635,41530210)
文摘An anomalous isotope effect exists in many heavy element isotope systems （e.g., Sr, Gd, Zn, U）. This effect used to be called the ＂odd--even isotope effect＂ because the odd mass number isotopes behave differently from the even mass number isotopes. This mass-indepen- dent isotope fractionation driving force, which originates from the difference in the ground-state electronic energies caused by differences in nuclear size and shape, is cur- rently denoted as the nuclear field shift effect （NFSE）. It is found that the NFSE can drive isotope fractionation of some heavy elements （e.g., Hg, T1, U） to an astonishing degree, far more than the magnitude caused by the con- ventional mass-dependent effect （MDE）. For light ele- ments, the MDE is the dominant factor in isotope fractionation, while the NFSE is neglectable. Furthermore, the MDE and the NFSE both decrease as temperatures increase, though at different rates. The MDE decreases rapidly with a factor of 1/T2, while the NFSE decreases slowly with a factor of 1/T. As a result, even at high temperatures, the NFSE is still significant for many heavy element isotope systems. In this review paper, we begin with an introduction of the basic concept of the NSFE, including its history and recent progress, and follow with the potential implications of the inclusion of the NFSE into the kinetic isotope fractionation effect （KIE） and heavy isotope geochronology.
基金supported by the financial support from the National Natural Science Foundation of China(Nos.51735005 and U1930207)the Basic Strengthening Program(No.2019-JCJQ-JJ-331)+1 种基金National Natural Science Founda-tion of China for Creative Research Groups(No.51921003)the 15th Batch of‘Six Talents Peaks’Innovative Talents Team Program(No.TD-GDZB-001).
文摘Laser additive manufacturing (AM) of lattice structures with light weight, excellent impact resistance, and energy absorption performance is receiving considerable attention in aerospace, transportation, and mechanical equipment application fields. In this study, we designed four gradient lattice structures (GLSs) using the topology optimization method, including the unidirectional GLS, the bi-directional increasing GLS, the bi-directional decreasing GLS and the none-GLS. All GLSs were manufactureed by laser powder bed fusion (LPBF). The uniaxial compression tests and finite element analysis were conducted to investigate the influence of gradient distribution features on deformation modes and energy absorption performance of GLSs. The results showed that, compared with the 45° shear fracture characteristic of the none-GLS, the unidirectional GLS, the bi-directional increasing GLS and the bi-directional decreasing GLS had the characteristics of the layer-by-layer fracture, showing considerably improved energy absorption capacity. The bi-directional increasing GLS showed a unique combination of shear fracture and layer-by-layer fracture, having the optimal energy absorption performance with energy absorption and specific energy absorption of 235.6 J and 9.5 J g-1 at 0.5 strain, respectively. Combined with the shape memory effect of NiTi alloy, multiple compression-heat recovery experiments were carried out to verify the shape memory function of LPBF-processed NiTi GLSs. These findings have potential value for the future design of GLSs and the realization of shape memory function of NiTi components through laser AM.
基金This work was supported by Hong Kong ITF research project (No. ITS 098/02).
文摘SMPU （shape memory polyurethane） non-ionomers and ionomers, synthesized with poly（c-caprolactone） （PCL）, 4, 4＇-diphenylmethane diisocyanate （MDI）, 1,4-butanediol （BDO）, dimethylolpropionic acid （DMPA） were measured with cyclic tensile test and strain recovery test. The relations between the structure and shape memory effect of these two series were studied with respect to the ionic group content and the effect of neutralization. The resulting data indicate that, with the introduction of asymmetrical extender, the stress at 100% elongation is decreased for PU non-ionomer and ionomer series, especially lowered sharply for non-ionomer series; the fixation ratio of ionomer series is not affected obviously by the ionic group content; the total recovery ratio of ionomer series is decreased greatly. After sufficient relaxation time for samples stretched beforehand, the switching temperature is raised slightly, whereas the recovery ratio measured with strain recovery test method is lowered with increased DMPA content. The characterization with FT-IR, DSC, DMA elucidated that, the ordered hard domain of the two series is disrupted with the introduction of DMPA which causes more hard segments to dissolve in soft phase; ionic groups on hard segment enhance the cohesion between hard segments especially at high ionic group content and significantly facilitate the phase separation compared with the corresponding non-ionomer at moderate ionic group content.
基金Financial supports by the National Natural Science Foundation of China (Grant 11532010)the project for Sichuan Provincial Youth Science and Technology Innovation Team, China (Grant 2013TD0004)
文摘A macroscopic based multi-mechanism constitutive model is constructed in the framework of irreversible thermodynamics to describe the degeneration of shape memory effect occurring in the thermo-mechanical cyclic deformation of NiTi shape memory alloys (SMAs). Three phases, austenite A, twinned martensite and detwinned martensite , as well as the phase transitions occurring between each pair of phases (, , , , and are considered in the proposed model. Meanwhile, two kinds of inelastic deformation mechanisms, martensite transformation-induced plasticity and reorientation-induced plasticity, are used to explain the degeneration of shape memory effects of NiTi SMAs. The evolution equations of internal variables are proposed by attributing the degeneration of shape memory effect to the interaction between the three phases (A, , and and plastic deformation. Finally, the capability of the proposed model is verified by comparing the predictions with the experimental results of NiTi SMAs. It is shown that the degeneration of shape memory effect and its dependence on the loading level can be reasonably described by the proposed model.
基金This work was supported by the National Natural Science Foundations of China(Grant 11272044)the Fundamental Research Funds for the Central Universities(Grant 2018JBM305).
文摘Shape memory polymers(SMPs)usually have a one-way shape memory effect.In this paper,an easy-operating method to realize a two-way shape memory effect was demonstrated in a ring-shaped bilayer structure where the two layers are SMPs with different thermal transition temperatures.By designing specific thermomechanical processes,the mismatched deformation between the two layers leads to a morphology change of ring-shaped bilayer structures from a smooth ring to a gear-like buckling shape under cooling and a reversible recovery to the smooth shape under heating.Such a morphology change is ascribed to occurrence and recovery of thermoelastic buckling.This method was validated by finite element simulation.We experimentally investigated the influence of pre-strain on buckling,and it was found that both the buckling occurrence and recovery temperature vary with pre-strain.Furthermore,considering a ring-shaped SMP-SMP bilayer structure,finite element analysis was conducted to study the influence of film thickness and modulus ratio of two layers on buckling behavior.The results showed that the critical buckling wavelength was greatly influenced by film thickness and modulus ratio.W e made a theoretical analysis that accorded well with the numerical results.
基金the National Natural Science Foundation of China(Nos.51731005,51822102 and 51527801)the Fundamental Research Funds for the Central Universities(grant No.FRF-TP-18-008C1)Use of the Advanced Photon Source was supported by the U.S.Department of Energy,Office of Science,Office of Basic Energy Science,under Contract No.DE-AC02-06CH11357.
文摘An intrinsic two-way shape memory effect with a fully recoverable strain of 1.0%was achieved in an as-prepared Ni50Mn37.5Sn12.5 metamagnetic shape memory microwire fabricated by Taylor-Ulitovsky method.This two-way shape memory effect is mainly owing to the internal stress caused by the retained martensite in austenite matrix,as revealed by transmission electron microscopy observations and highenergy X-ray diffraction experiments.After superelastic training for 30 loading/unloading cycles at room temperature,the amount of retained martensite increased and the recoverable strain of two-way shape memory effect increased significantly to 2.2%.Furthermore,a giant recoverable strain of 11.2%was attained under a bias stress of 300 MPa in the trained microwire.These properties confer this microwire great potential for micro-actuation applications.
文摘With the development of radioactive-ion-beam facilities,many exotic phenomena have been discovered or predicted in the nuclei far from the stability line,including cluster structure,shell structure,deformed halo,and shape decoupling effects.The study of exotic nuclear phenomena is at the frontier of nuclear physics nowadays.The covariant density functional theory(CDFT)is one of the most successful microscopic models in describing the structure of nuclei in almost the whole nuclear chart.Within the framework of CDFT,toward a proper treatment of deformation and weak binding,the deformed relativistic Hartree-Bogoliubov theory in continuum(DRHBc)has been developed.In this contribution,we review the applications and extensions of the DRHBc theory to the study of exotic nuclei.The DRHBc theory has been used to investigate the deformed halos in B,C,Ne,Na,and Mg isotopes and the theoretical descriptions are reasonably consistent with available data.A DRHBc Mass Table Collaboration has been founded,aiming at a high precision nuclear mass table with deformation and continuum effects included,which is underway.By implementing the angular momentum projection based on the DRHBc theory,the rotational excitations of deformed halos have been investigated and it is shown that the deformed halos and shape decoupling effects also exist in the low-lying rotational excitation states of deformed halo nuclei.
文摘The influence of aging on the microstructure and mechanical properties of Cu-11.6wt%Al-3.9wt%Ni-2.5wt%Mn shape memory alloy（SMA） was studied by means of scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray diffractometer,and differential scanning calorimeter（DSC）.Experimental results show that bainite,γ2,and α phase precipitates occur with the aging effect in the alloy.After aging at 300°C,the bainitic precipitates appear at the early stages of aging,while the precipitates of γ2 phase are observed for a longer aging time.When the aging temperature increases,the bainite gradually evolves into γ2 phase and equilibrium α phase（bcc） precipitates from the remaining parent phase.Thus,the bainite,γ2,and α phases appear,while the martensite phase disappears progressively in the alloy.The bainitic precipitates decrease the reverse transformation temperature while the γ2 phase precipitates increase these temperatures with a decrease of solute content in the retained parent phase.On the other hand,these precipitations cause an increasing in hardness of the alloy.
基金supported by the National Natural Science Foundation of China (No.50971007)the Program for New Century Excellent Talents in Universities from the Ministry of Education of China (No.NCET-09-0024)
文摘A NiTi shape memory alloy （SMA） modified by Ta ion implantation was subjected to oxidation treatment in air at 723 and 873 K. Atomic force microscopy （AFM）, Auger electron spectroscopy （AES）, and grazing incidence X-ray diffraction （GIXRD） measurements were conducted to investigate the surface characteristics, including surface topography, elemental depth profiles, and surface phase structures. The surface roughness of the Ta-implanted NiTi increases after oxidation, and the higher the oxidation temperature is, the larger the value is. The surface of the Ta-implanted NiTi oxidized at 723 K is a nanolayer mainly composed of TiO2/Ta2O5 and TiO with depressed Ni content. The Ta-implanted NiTi oxidized at 873 K is mainly covered by rutile TiO2 in several micrometers of thickness. Potentiodynamic polarization tests indicated that the corrosion resistance of the Ta-implanted NiTi was improved after thermal oxidation at 723 K, but a negative impact was found for the Ta-implanted NiTi oxidized at 873 K.
文摘Improvement of shape, memory effect (SME) in Fe-Mn-Si based alloys has been investigated, compared with that by conventional 'training' treatment. It is found that SME in Fe-Mn-Si alloy can be greatly improved by ausforming and 3.8%recovery strain and 2.2% complete recovery strain can be reached by ausforming at 973 K when dynamic recrystallization has just occurred. The mechanism for the improvement of SME is proposed.
基金The project is financially supported by the National Natural Science Foundation of China ( No 50531020)
文摘The microstructure,phase transformation,compression property and strain recovery characteristics of equiatomic Ru-Nb high temperature shape memory alloy were investigated by means of optical microscope,X-ray diffraction(XRD),differential scanning calorimetry(DSC),compression tests and transmission electron microscopy(TEM).When cooling the alloy specimen from high temperature to room temperature,β(parent phase)→β’(interphase)→β″(martensite) two step phase transformation occurs.The microstructure at room temperature shows regularly arranged band morphology with the monoclinic crystal structure.The twinning relationship between the martensite bands was determined to be(101) Type I.Reorientation and of the martensite bands inside the variant and dislocation were found during compression at room temperature.The maximum complete recovery strain is about 1.5%.
基金support of the 111 Project(No.B18017)the National Equipment Pre-Research Project of the 13th Five-Year Plan(No.30508040601)。
文摘The effects of 1 Me V electron irradiation in air at a fixed accumulated dose and dose rates of 393.8,196.9,78.8,and 39.4 Gy s^(-1)on a shape memory epoxy(SMEP)resin were studied.Under low-dose-rate irradiation,accelerated degradation of the shape memory performance was observed;specifically,the shape recovery ratio decreased exponentially with increasing irradiation time(that is,with decreasing dose rate).In addition,the glass transition temperature of the SMEP,as measured by dynamic mechanical analysis,decreased overall with decreasing dose rate.The dose rate effects of 1 Me V electron irradiation on the SMEP were confirmed by structural analysis using electron paramagnetic resonance(EPR)spectroscopy and Fourier transform infrared(FTIR)spectroscopy.The EPR spectra showed that the concentration of free radicals increased exponentially with increasing irradiation time.Moreover,the FTIR spectra showed higher intensities of the peaks at 1660 and 1720 cm^(-1),which are attributed to stretching vibrations of amide C=O and ketone/acid C=O,at lower dose rates.The intensities of the IR peaks at 1660 and 1720 cm^(-1) increased exponentially with increasing irradiation time,and the relative intensity of the IR peak at 2926 cm^(-1)decreased exponentially with increasing irradiation time.The solid-state13 C nuclear magnetic resonance(NMR)spectra of the SMEP before and after 1 Me V electron irradiation at a dose of 1970 k Gy and a dose rate of 78.8 Gy s^(-1) indicated damage to the CH_(2)–N groups and aliphatic isopropanol segment.This result is consistent with the detection of nitrogenous free radicals,a phenoxy-type free radical,and several types of pyrolytic carbon radicals by EPR.During the subsequent propagation process,the free radicals produced at lower dose rates were more likely to react with oxygen,which was present at higher concentrations,and form the more destructive peroxy free radicals and oxidation products such as acids,amides,and ketones.The increase in peroxy free radicals at lower dose rates was thought to accelerate the degradation of the macroscopic performance of the SMEP.
文摘A two-way shape memory effect (TWSM E) in the Ti46.3Ni44.7Nb9 alloy has been systematically investigated by means of bending test and transmission electron microscopy (TEM ) observations. Based on the analysis of the microstructure after training. the mechanism of TWSME in the Ti46.3 Ni44.7Nb9 alloy has been discussed.
基金financially supported by the National Natural Science Foundation of China(Nos.81622032,51672184,51525101and 51472279)the Priority Academic Program Development of Jiangsu High Education Institutions(PAPD)+2 种基金the Jiangsu Innovation and Entrepreneurship Program,the National Basic Research Program of China(973 Program,No.2014CB748600)the Jiangsu Provincial Special Program of Medical Science(No.BL2012004)the Jiangsu Six Peak of Talents Program(No.2013-WSW-056)
文摘Natural diatomite （DT） is the ancient deposit of diatom skeleton with many regular pores of 50-200 nm and also an abundant source of biogenic silica. Although silica is considered biologically safe and there is an increasing interest of using natural diatomite for biomedical applications, the toxicity information about natural diatomite is still missing. Here, cytotoxicity of natural diatomite on osteoblasts and fibroblasts were compared to hydroxyapatite and the relationships between cytotoxicity and diatomite sizes, dose, geometry or impurity were systematically investigated. Cell adhesion and interaction with diatomite particles were also fluorescently observed, The results clearly suggested a size-, dose- and shape-dependent cytotoxicity of natural diatomite. Disk-shaped diatomite particles with average size of 30μm in diameter revealed the least toxicity, while the diatomite particles with irregular shapes and sizes less than 10 μm were remarkably toxic. Diatomite particles with proper sizes were then selected to investigate the reinforcing effect on injectable calcium phosphate bone cement. Results showed that diatomite significantly improved the compressive strength of bone cement but did not alter the injectability of the cement, This work provided important biocompatibility information of natural diatomite and demonstrated the feasibility of using selected diatomite as bone implant material.
文摘The Effect of the thermal cycling training under constant strain on the two-way shape memory effect (TWSME) in a Ti36l\li49Hf15 high temperature shape memory alloy (SMA) has been investigated by bending tests. The results indicated that the training procedure is beneficial to get the better TWSME. The two-way shape memory strain increases with increasing the training strain. And it decreases with increasing the training temperature. The TWSME obtained in the present alloy shows poorer stability compared with that obtained in the TiNi alloys.
