This paper is devoted to developing a yield criterion that can model the asymmetry and anisotropy in yielding of pressure insensitive metals,in terms of accuracy and simplicity of formulation.First,a new isotropic yie...This paper is devoted to developing a yield criterion that can model the asymmetry and anisotropy in yielding of pressure insensitive metals,in terms of accuracy and simplicity of formulation.First,a new isotropic yield criterion,which can model the asymmetry in yielding of pressure insensitive metals,is proposed.Further,using Cazacu's generalizations to anisotropic conditions of the invariants of the deviatoric stress,the proposed isotropic yield criterion is extended to orthotropy.The proposed anisotropic criterion has a quite simple form,and the number of material constants involved is only half of that of Cazacu's(2004) yield criterion.Compared to Hill's(1948) yield criterion,the proposed anisotropic yield criterion has three additional constants,which are used to model the tension-compression asymmetry of materials.All the material constants involved in the criterion can be determined by simple tests.The proposed criterion reduces to Hill's(1948) yield criterion if the tensile and compressive yield stresses are equal.In other words,the proposed anisotropic yield criterion can be considered as an extension of Hill's(1948) criterion to tension-compression asymmetry materials.The anisotropic yield criterion is used to describe the plastic response of Cu-Al-Be shape memory alloy(data after Laydi and Lexcellent) and Ni3Al based intermetallic alloy IC10 sheets.It is shown that the proposed yield criterion can describe very well the asymmetry and anisotropy observed in those materials.展开更多
塑性变形是金属材料在应力作用下产生损伤的早期阶段,对其的有效检测可预判危害的发生,实现设备破坏前的预警。针对金属磁记忆检测技术,利用量子力学密度泛函理论建立铁磁材料力磁耦合计算模型,采用原子轨道正交化线性组合法(Orthogonal...塑性变形是金属材料在应力作用下产生损伤的早期阶段,对其的有效检测可预判危害的发生,实现设备破坏前的预警。针对金属磁记忆检测技术,利用量子力学密度泛函理论建立铁磁材料力磁耦合计算模型,采用原子轨道正交化线性组合法(Orthogonalized linear combination atomic orbitals,OLCAO)计算铁磁晶体在应力作用下的磁特性变化及磁记忆信号特征。结果表明:应力作用引起晶体内部电子运动状态及其分布特征改变,导致体系能带结构和电子态密度分布发生变化,材料的磁特性发生改变,定量表现为原子磁矩随应力的增加而变化。拉应力导致原子磁矩线性减小,压应力导致原子磁矩线性增大。当金属发生塑性变形时,体系的磁矩均发生突变,应力磁矩关系曲线出现拐点,变化速度变慢,表现为磁记忆信号的特殊变化特征。通过铁磁材料的拉伸及压缩试验,验证了理论计算结果的正确性。展开更多
The present work is concerned with the characterization of hardening parameters for an elasto-plastic continuum model, taking into account the memory effect of plastic strain amplitude, in order to predict the hystere...The present work is concerned with the characterization of hardening parameters for an elasto-plastic continuum model, taking into account the memory effect of plastic strain amplitude, in order to predict the hysteretic responses of a ferritic steel. This elasto-plastic three-dimensional model is based on the internal thermodynamic variables which composed of the nonlinear kinematic hardening and isotropic hardening with the plastic strain memorization. The emphasis is put on the determination of strain memory parameters along with other material parameters of the proposed model in order to better simulate the behavior of the material at different strain range. The material parameters are calibrated with the experimental stabilized loops of stress-strain curves available in the literature. The predicted stabilized loops from the simulation with the determined parameters show good agreement with the experimental results signifying the validity of the considered model.展开更多
The recovery force or recovery strain is an important indicator of NiTi-based shape memory alloy devices. However, the restoring force or recoverable strain is partially restrained due to an interaction between reorie...The recovery force or recovery strain is an important indicator of NiTi-based shape memory alloy devices. However, the restoring force or recoverable strain is partially restrained due to an interaction between reorientation and reorientation-induced plasticity. Therefore, a macroscopic multi-mechanism constitutive model was constructed to describe the degeneration of shape memory effect based on the phase diagram. The residual strain after cooling consists of reorientation strain and reorientation-induced plastic strain. An internal variable, i.e., the detwinned stress, and its evolution equation were introduced into the transformation kinetics equation to describe the nonlinear hardening characteristics induced by the combined reorien- ration and detwinning mechanisms during mechanical loading. Finally, the proposed model was numerically implemented to simulate the experiments of shape memory effect at different peak strains. Comparisons between the experimental and simulated results show that the proposed model can reasonably describe the degeneration of shape memory effect.展开更多
Detecting stress concentration, especially critical stress state leading to structure damage or failure, is one of the most important tasks of equipment diagnosis. Metal magnetic memory technique needs further researc...Detecting stress concentration, especially critical stress state leading to structure damage or failure, is one of the most important tasks of equipment diagnosis. Metal magnetic memory technique needs further research to evaluate stress concentration quantitatively due to ambiguous physical mechanism, though it has potential to detect early defects in ferromagnetic materials. Mild Q235 steel defective specimens in demagnetization state were loaded in tension up to visible necking, with magnetic memory signals measurement made at increasing stress levels. Magnetic signals varied greatly under first several loadings and subsequently tended to stability in the elastic region, which showed that the magnetization always approaches the anhysteretic magnetization curve and was explained by the theory of magnetomechanical effect. In the plastic stage, an abnormal wave occurred in the stress concentration zone and its height value was sensitive to plastic deformation levels and dependent on the distance between the probe and defect, in accordance with the simulation results based on the magnetic dipole model. Different magnetic signal characteristics in the elastic-plastic region indicate that the magnetic memory technique can identify macroyielding and early damage, which is of profound significance for ensuring safe operation of equipment in service.展开更多
Nickel-titanium shape memory alloy （NiTi SMA） which possesses crystal structure of B2 austenite at room temperature was subjected to plastic deformation at low temperature （-150 ℃） by means of local canning compr...Nickel-titanium shape memory alloy （NiTi SMA） which possesses crystal structure of B2 austenite at room temperature was subjected to plastic deformation at low temperature （-150 ℃） by means of local canning compression. The microstructural evolution of NiTi SMA at the different deformation degree was investigated by transmission electron microscopy （TEM） and high resolution transmission electron microscopy （HRTEM）. At the deformation degree by 15%, a high density of dislocations occurs in the deformed NiTi sample. At the deformation degree by 25%, the deformed NiTi sample exhibits the martensite morphology due to the pinning of dislocations at the grain boundaries. At the deformation degree by 50%, a small amount of nanocrystalline phase arises in the deformed NiTi sample. At the deformation degree by 80%, severe plastic deformation （SPD） leads to the occurrence of a great deal of amorphous and nanocrystalline phase,展开更多
The paper presents a complex method of forming the surface-modified layers of materials with shape memory effect, including high-speed flame spraying of powders based on TiNiCo;subsequent thermal and thermomechanical ...The paper presents a complex method of forming the surface-modified layers of materials with shape memory effect, including high-speed flame spraying of powders based on TiNiCo;subsequent thermal and thermomechanical treatment allows the formation of surface layers of nano-sized state that have a high level of functional, mechanical and performance properties;it is shown that the complex processing with a layer of TiNiCo allows a reduction of the porosity of the coatings and increases the strength of the coating’s adhesion to the substrate. It is found that, after treatment with high-speed flame spraying powder shape memory TiNiCo, steel has an increase in cycle life by 30% - 40% in a cycle fatigue and 3 - 3.5 times durability. Based on comprehensive research into the metallophysical surface-modified layer, new information is obtained about the nanoscale composition.展开更多
Objective:Drainage tubes(e.g.,intracranial,abdominal cavity and thoracic)are commonly used to drain blood and fluid collections after surgery.It usually fails due to the lack of fixation perpendicular to the skin and ...Objective:Drainage tubes(e.g.,intracranial,abdominal cavity and thoracic)are commonly used to drain blood and fluid collections after surgery.It usually fails due to the lack of fixation perpendicular to the skin and the variety of tube materials.The objective of the article is to describe a new drainage tube device.Methods:This new device consists of a drainage tube fixator and diverter with a rotating handle.The fixator and diverter are fixed to the skin with a pair of wings,and the base comprises acircular arc with chamfering of the edge.The removable stopper and plastic diverter have a memory function.There are 2 holes on either side of the wings,by which they can be sewn to the skin or stapled for strength and stability.Results:The removable limiting stopper and plastic diverter with memory function work together to ensure that the drainage tube is firmly fixed.Therefore,the tube will not move either vertically or horizontally on the skin.Moreover,the device is fit for drainage tubes with different specifications and materials.Conclusions:The limiting stopper can be moved easily,which is conducive to local skin disinfection around the drainage tube.The device deserves clinical promotion.展开更多
文摘This paper is devoted to developing a yield criterion that can model the asymmetry and anisotropy in yielding of pressure insensitive metals,in terms of accuracy and simplicity of formulation.First,a new isotropic yield criterion,which can model the asymmetry in yielding of pressure insensitive metals,is proposed.Further,using Cazacu's generalizations to anisotropic conditions of the invariants of the deviatoric stress,the proposed isotropic yield criterion is extended to orthotropy.The proposed anisotropic criterion has a quite simple form,and the number of material constants involved is only half of that of Cazacu's(2004) yield criterion.Compared to Hill's(1948) yield criterion,the proposed anisotropic yield criterion has three additional constants,which are used to model the tension-compression asymmetry of materials.All the material constants involved in the criterion can be determined by simple tests.The proposed criterion reduces to Hill's(1948) yield criterion if the tensile and compressive yield stresses are equal.In other words,the proposed anisotropic yield criterion can be considered as an extension of Hill's(1948) criterion to tension-compression asymmetry materials.The anisotropic yield criterion is used to describe the plastic response of Cu-Al-Be shape memory alloy(data after Laydi and Lexcellent) and Ni3Al based intermetallic alloy IC10 sheets.It is shown that the proposed yield criterion can describe very well the asymmetry and anisotropy observed in those materials.
文摘塑性变形是金属材料在应力作用下产生损伤的早期阶段,对其的有效检测可预判危害的发生,实现设备破坏前的预警。针对金属磁记忆检测技术,利用量子力学密度泛函理论建立铁磁材料力磁耦合计算模型,采用原子轨道正交化线性组合法(Orthogonalized linear combination atomic orbitals,OLCAO)计算铁磁晶体在应力作用下的磁特性变化及磁记忆信号特征。结果表明:应力作用引起晶体内部电子运动状态及其分布特征改变,导致体系能带结构和电子态密度分布发生变化,材料的磁特性发生改变,定量表现为原子磁矩随应力的增加而变化。拉应力导致原子磁矩线性减小,压应力导致原子磁矩线性增大。当金属发生塑性变形时,体系的磁矩均发生突变,应力磁矩关系曲线出现拐点,变化速度变慢,表现为磁记忆信号的特殊变化特征。通过铁磁材料的拉伸及压缩试验,验证了理论计算结果的正确性。
文摘The present work is concerned with the characterization of hardening parameters for an elasto-plastic continuum model, taking into account the memory effect of plastic strain amplitude, in order to predict the hysteretic responses of a ferritic steel. This elasto-plastic three-dimensional model is based on the internal thermodynamic variables which composed of the nonlinear kinematic hardening and isotropic hardening with the plastic strain memorization. The emphasis is put on the determination of strain memory parameters along with other material parameters of the proposed model in order to better simulate the behavior of the material at different strain range. The material parameters are calibrated with the experimental stabilized loops of stress-strain curves available in the literature. The predicted stabilized loops from the simulation with the determined parameters show good agreement with the experimental results signifying the validity of the considered model.
基金Financial supports by the National Natural Science Foundation of China （Nos. 11572265, 11532010）, the Excellent Youth Found of Sichuan Province （No. 2017JQ0019）
文摘The recovery force or recovery strain is an important indicator of NiTi-based shape memory alloy devices. However, the restoring force or recoverable strain is partially restrained due to an interaction between reorientation and reorientation-induced plasticity. Therefore, a macroscopic multi-mechanism constitutive model was constructed to describe the degeneration of shape memory effect based on the phase diagram. The residual strain after cooling consists of reorientation strain and reorientation-induced plastic strain. An internal variable, i.e., the detwinned stress, and its evolution equation were introduced into the transformation kinetics equation to describe the nonlinear hardening characteristics induced by the combined reorien- ration and detwinning mechanisms during mechanical loading. Finally, the proposed model was numerically implemented to simulate the experiments of shape memory effect at different peak strains. Comparisons between the experimental and simulated results show that the proposed model can reasonably describe the degeneration of shape memory effect.
基金supported by National Natural Science Foundation of China(Grant No. 10772061)Heilongjiang Provincial Natural Science Foundation of China(Grant No. A200907)Specialized Research Fundfor the Doctoral Program of Higher Education of China(Grant No.20092322120001)
文摘Detecting stress concentration, especially critical stress state leading to structure damage or failure, is one of the most important tasks of equipment diagnosis. Metal magnetic memory technique needs further research to evaluate stress concentration quantitatively due to ambiguous physical mechanism, though it has potential to detect early defects in ferromagnetic materials. Mild Q235 steel defective specimens in demagnetization state were loaded in tension up to visible necking, with magnetic memory signals measurement made at increasing stress levels. Magnetic signals varied greatly under first several loadings and subsequently tended to stability in the elastic region, which showed that the magnetization always approaches the anhysteretic magnetization curve and was explained by the theory of magnetomechanical effect. In the plastic stage, an abnormal wave occurred in the stress concentration zone and its height value was sensitive to plastic deformation levels and dependent on the distance between the probe and defect, in accordance with the simulation results based on the magnetic dipole model. Different magnetic signal characteristics in the elastic-plastic region indicate that the magnetic memory technique can identify macroyielding and early damage, which is of profound significance for ensuring safe operation of equipment in service.
基金Funded by National Natural Science Foundation of China(No.51071056)the Fundamental Research Funds for the Central Universities of China(Nos.HEUCF121712 and HEUCF201317002)
文摘Nickel-titanium shape memory alloy （NiTi SMA） which possesses crystal structure of B2 austenite at room temperature was subjected to plastic deformation at low temperature （-150 ℃） by means of local canning compression. The microstructural evolution of NiTi SMA at the different deformation degree was investigated by transmission electron microscopy （TEM） and high resolution transmission electron microscopy （HRTEM）. At the deformation degree by 15%, a high density of dislocations occurs in the deformed NiTi sample. At the deformation degree by 25%, the deformed NiTi sample exhibits the martensite morphology due to the pinning of dislocations at the grain boundaries. At the deformation degree by 50%, a small amount of nanocrystalline phase arises in the deformed NiTi sample. At the deformation degree by 80%, severe plastic deformation （SPD） leads to the occurrence of a great deal of amorphous and nanocrystalline phase,
文摘The paper presents a complex method of forming the surface-modified layers of materials with shape memory effect, including high-speed flame spraying of powders based on TiNiCo;subsequent thermal and thermomechanical treatment allows the formation of surface layers of nano-sized state that have a high level of functional, mechanical and performance properties;it is shown that the complex processing with a layer of TiNiCo allows a reduction of the porosity of the coatings and increases the strength of the coating’s adhesion to the substrate. It is found that, after treatment with high-speed flame spraying powder shape memory TiNiCo, steel has an increase in cycle life by 30% - 40% in a cycle fatigue and 3 - 3.5 times durability. Based on comprehensive research into the metallophysical surface-modified layer, new information is obtained about the nanoscale composition.
基金Supported by the Zhejiang Province Traditional Chinese Medicine Project On Technology(No.2015ZA209)
文摘Objective:Drainage tubes(e.g.,intracranial,abdominal cavity and thoracic)are commonly used to drain blood and fluid collections after surgery.It usually fails due to the lack of fixation perpendicular to the skin and the variety of tube materials.The objective of the article is to describe a new drainage tube device.Methods:This new device consists of a drainage tube fixator and diverter with a rotating handle.The fixator and diverter are fixed to the skin with a pair of wings,and the base comprises acircular arc with chamfering of the edge.The removable stopper and plastic diverter have a memory function.There are 2 holes on either side of the wings,by which they can be sewn to the skin or stapled for strength and stability.Results:The removable limiting stopper and plastic diverter with memory function work together to ensure that the drainage tube is firmly fixed.Therefore,the tube will not move either vertically or horizontally on the skin.Moreover,the device is fit for drainage tubes with different specifications and materials.Conclusions:The limiting stopper can be moved easily,which is conducive to local skin disinfection around the drainage tube.The device deserves clinical promotion.
