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
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
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.
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.