Ni_(47)Ti_(44)Nb_(9)shape memory alloy(SMA)is a promising material in the aerospace field due to its wide transformation hysteresis.The application of shape memory effect depends on multistep thermomechan-ical loading...Ni_(47)Ti_(44)Nb_(9)shape memory alloy(SMA)is a promising material in the aerospace field due to its wide transformation hysteresis.The application of shape memory effect depends on multistep thermomechan-ical loading,viz.,low-temperature deformation and subsequent heating to recovery.Low-temperature deformation prestrain plays a pivotal role in shape memory properties tailoring of SMA components.However,microstructure evolution and deformation mechanisms of Ni_(47)Ti_(44)Nb_(9)SMA subjected to vari-ous prestrain levels are still unclear.To this end,microstructure evolution and shape memory behaviors of Ni_(47)Ti_(44)Nb_(9)alloy subjected to multistep thermomechanical loading with prestrain levels of 8%-16%at-28℃(M_(s)+30℃)were investigated.The results demonstrate that the stress-strain curve of the specimen exhibits four distinct stages at a maximal prestrain of 16%.Whereas stageⅡand stageⅢend at prestrains of∼8%and∼12%,respectively.In stageⅡ,the stress-induced martensitic transformation is accompanied by the dislocation slip of the NiTi matrix andβ-Nb inclusions.In stageⅢ,in addition to the higher density of dislocations and further growth of stress-induced martensite variants(SIMVs),(001)compound twins are introduced as a result of the(001)deformation twinning in stress-induced martensite.More{20-1}martensite twins are gradually introduced in stageⅣ.Correspondingly,after subsequent unloading and heating,a higher density of{114}austenite twins form in the specimen with a larger prestrain of 16%.With increasing prestrain from 8%to 16%,the recoverable strainε_(re)^(T)upon heating increases first and then decreases.Theε_(re)^(T)obtains a maximum of 7.03%at 10%prestrain and de-creases to 6.17%at 16%prestrain.The increase ofε_(re)^(T)can be attributed to the formation of new SIMVs,the further growth of existing SIMVs,and the recoverable(001)compound twins.While the decrease ofε_(re)^(T)is mainly associated with the irrecoverable strain by{20−1}martensite twins.The effect ofβ-Nb inclusions o展开更多
By choosing the dissipation energy as the damage variable,corresponding damage evolution equations are established,respectively,for the mechanical cyclic loading part and the thermal one during the thermo-mechanical c...By choosing the dissipation energy as the damage variable,corresponding damage evolution equations are established,respectively,for the mechanical cyclic loading part and the thermal one during the thermo-mechanical cyclic loading of NiTi shape memory alloys(SMAs)involving one-way shape memory effect(simply denoted as the OWSME cycling).And then,the evolution law of total damage is obtained by a superposition of such two damage parts.Finally,the uniaxial OWSME fatigue lives of NiTi SMA micro-tubes are predicted by combining the proposed damage model with an adopted failure criterion.The results show that all the predicted fatigue lives are located within the twice scatter band with regard to the experimental ones,and most of them are located within a scatter band of 1.5 times.It is indicated that the predicted OWSME fatigue lives are in good agreement with the experimental ones.展开更多
Research on microcapsules has been conducted in recent years given trends in miniaturization and novel functionalization.In this work,we designed and prepared a series of unique shape memory polyurethane(SMPU)microcap...Research on microcapsules has been conducted in recent years given trends in miniaturization and novel functionalization.In this work,we designed and prepared a series of unique shape memory polyurethane(SMPU)microcapsules with stimuli-responsive func-tions.The microcapsule has a core-shell structure in which the surface morphology can be adjusted,and it has a certain loadbearing capacity.In addition,the SMPU microcapsule has a stimuliresponsive function for shape memory and solvent response.The temperature of its shape recovery is approximately body tempera-ture,and it can swell to rupture under the stimulation of organic solvents.Thus,the SMPU microcapsule has potential applications in biomedical fields,such as drug release.展开更多
A new finite strain elatoplastic J2-flow model with coupling effects of both isotropic and anisotropic hardening is proposed with the co-rotational logarithmic rate.In terms of certain single-variable shape functions ...A new finite strain elatoplastic J2-flow model with coupling effects of both isotropic and anisotropic hardening is proposed with the co-rotational logarithmic rate.In terms of certain single-variable shape functions representing uniaxial loading and unloading curves,explicit multi-axial expressions for the three hardening quantities incorporated in the new model proposed are derived in unified forms for the purpose of automatically and accurately simulating complex pseudoelastic-to-plastic transition effects of shape memory alloys(SMAs)under multiple loading-unloading cycles.Numerical examples show that with only a single parameter of direct physical meaning for each cycle,accurate and explicit simulations may be achieved for extensive data from multiple cycle tests.展开更多
The cyclic transformation behaviors of polycrystalline super-elastic NiTi shape memory alloys (SMAs)under multiaxial loading paths with different angles between axial and torsional loading orientations were experiment...The cyclic transformation behaviors of polycrystalline super-elastic NiTi shape memory alloys (SMAs)under multiaxial loading paths with different angles between axial and torsional loading orientations were experimentally investigated.The experimental results showed that the start stresses of forward and reverse transformations decreased with the increase'in the number of cycles and exhibit obvious anisotropic evolutions.The start stresses of forward and reverse transformations in the tensile and torsional directions did not satisfy the yon Mises criterion.The shape of transformation surface during the forward and reverse transformations evolved with the increase in the number of cycles.Then,new cyclic anisotropic transformation surfaces were established by introducing an anisotropic tensor into the von Mises equivalent stress based on a typical transformation criterion related to J2 and J3.Moreover,the evolution equations of material parameters used in the proposed transformation surfaces were established to describe the subsequent evolutions of transformation surfaces.Finally,the start stresses of forward and reverse transformations predicted using the proposed transformation surfaces were compared with the experimental results.It shows that the proposed transformation surfaces can reasonably describe the start stresses of forward and reverse transformations,which are helpful for establishing a three-dimensional cyclic constitutive model to describe the cyclic transformation behaviors of super-elastic NiTi SMAs.展开更多
基金support from the National Natural Science Foundation of China(No.51775441)the National Science Fund for Excellent Young Scholars(No.51522509).
文摘Ni_(47)Ti_(44)Nb_(9)shape memory alloy(SMA)is a promising material in the aerospace field due to its wide transformation hysteresis.The application of shape memory effect depends on multistep thermomechan-ical loading,viz.,low-temperature deformation and subsequent heating to recovery.Low-temperature deformation prestrain plays a pivotal role in shape memory properties tailoring of SMA components.However,microstructure evolution and deformation mechanisms of Ni_(47)Ti_(44)Nb_(9)SMA subjected to vari-ous prestrain levels are still unclear.To this end,microstructure evolution and shape memory behaviors of Ni_(47)Ti_(44)Nb_(9)alloy subjected to multistep thermomechanical loading with prestrain levels of 8%-16%at-28℃(M_(s)+30℃)were investigated.The results demonstrate that the stress-strain curve of the specimen exhibits four distinct stages at a maximal prestrain of 16%.Whereas stageⅡand stageⅢend at prestrains of∼8%and∼12%,respectively.In stageⅡ,the stress-induced martensitic transformation is accompanied by the dislocation slip of the NiTi matrix andβ-Nb inclusions.In stageⅢ,in addition to the higher density of dislocations and further growth of stress-induced martensite variants(SIMVs),(001)compound twins are introduced as a result of the(001)deformation twinning in stress-induced martensite.More{20-1}martensite twins are gradually introduced in stageⅣ.Correspondingly,after subsequent unloading and heating,a higher density of{114}austenite twins form in the specimen with a larger prestrain of 16%.With increasing prestrain from 8%to 16%,the recoverable strainε_(re)^(T)upon heating increases first and then decreases.Theε_(re)^(T)obtains a maximum of 7.03%at 10%prestrain and de-creases to 6.17%at 16%prestrain.The increase ofε_(re)^(T)can be attributed to the formation of new SIMVs,the further growth of existing SIMVs,and the recoverable(001)compound twins.While the decrease ofε_(re)^(T)is mainly associated with the irrecoverable strain by{20−1}martensite twins.The effect ofβ-Nb inclusions o
基金Financial support of the National Natural Science Foundation of China(No.11532010)is appreciated。
文摘By choosing the dissipation energy as the damage variable,corresponding damage evolution equations are established,respectively,for the mechanical cyclic loading part and the thermal one during the thermo-mechanical cyclic loading of NiTi shape memory alloys(SMAs)involving one-way shape memory effect(simply denoted as the OWSME cycling).And then,the evolution law of total damage is obtained by a superposition of such two damage parts.Finally,the uniaxial OWSME fatigue lives of NiTi SMA micro-tubes are predicted by combining the proposed damage model with an adopted failure criterion.The results show that all the predicted fatigue lives are located within the twice scatter band with regard to the experimental ones,and most of them are located within a scatter band of 1.5 times.It is indicated that the predicted OWSME fatigue lives are in good agreement with the experimental ones.
基金the National Natural Science Foundation of China(Grant No.11802075,12072094).
文摘Research on microcapsules has been conducted in recent years given trends in miniaturization and novel functionalization.In this work,we designed and prepared a series of unique shape memory polyurethane(SMPU)microcapsules with stimuli-responsive func-tions.The microcapsule has a core-shell structure in which the surface morphology can be adjusted,and it has a certain loadbearing capacity.In addition,the SMPU microcapsule has a stimuliresponsive function for shape memory and solvent response.The temperature of its shape recovery is approximately body tempera-ture,and it can swell to rupture under the stimulation of organic solvents.Thus,the SMPU microcapsule has potential applications in biomedical fields,such as drug release.
基金Project supported by the National Natural Science Foundation of China(No.11372172)and the Start-up Fund from Jinan University in Guangzhou of China。
文摘A new finite strain elatoplastic J2-flow model with coupling effects of both isotropic and anisotropic hardening is proposed with the co-rotational logarithmic rate.In terms of certain single-variable shape functions representing uniaxial loading and unloading curves,explicit multi-axial expressions for the three hardening quantities incorporated in the new model proposed are derived in unified forms for the purpose of automatically and accurately simulating complex pseudoelastic-to-plastic transition effects of shape memory alloys(SMAs)under multiple loading-unloading cycles.Numerical examples show that with only a single parameter of direct physical meaning for each cycle,accurate and explicit simulations may be achieved for extensive data from multiple cycle tests.
基金National Natural Science Foundation of China (1157226511532010),the Excellent Youth Found of Sichuan Province (2017JQ0019),the Open Project of Traction Power State Key Laboratory (TPL1606)and the Exploration Project of Traction Power State Key Laboratory (2017TPL_T04)are acknowledged.
文摘The cyclic transformation behaviors of polycrystalline super-elastic NiTi shape memory alloys (SMAs)under multiaxial loading paths with different angles between axial and torsional loading orientations were experimentally investigated.The experimental results showed that the start stresses of forward and reverse transformations decreased with the increase'in the number of cycles and exhibit obvious anisotropic evolutions.The start stresses of forward and reverse transformations in the tensile and torsional directions did not satisfy the yon Mises criterion.The shape of transformation surface during the forward and reverse transformations evolved with the increase in the number of cycles.Then,new cyclic anisotropic transformation surfaces were established by introducing an anisotropic tensor into the von Mises equivalent stress based on a typical transformation criterion related to J2 and J3.Moreover,the evolution equations of material parameters used in the proposed transformation surfaces were established to describe the subsequent evolutions of transformation surfaces.Finally,the start stresses of forward and reverse transformations predicted using the proposed transformation surfaces were compared with the experimental results.It shows that the proposed transformation surfaces can reasonably describe the start stresses of forward and reverse transformations,which are helpful for establishing a three-dimensional cyclic constitutive model to describe the cyclic transformation behaviors of super-elastic NiTi SMAs.
