A coupled thermal-mechanical model of the rotary swaging of pure magnesium was developed using the general finite-element software program MSC/Marc to visualize the effect of axial feeding velocity on the rotary swagi...A coupled thermal-mechanical model of the rotary swaging of pure magnesium was developed using the general finite-element software program MSC/Marc to visualize the effect of axial feeding velocity on the rotary swaging process. The radial displacement occurring in one pulse impact increases in proportion to axial feeding velocity (vax). When the other processing parameters are fixed, the surface roughness of the swaged bar increases with vax and is in parabolic relation with vax. There exists a minimum velocity vax, min below which the decrease of vax will no longer improve the surface roughness. Under the technological conditions of this simulation, when the finial diameter d=6.6 mm, vax, min=1.82 m/min, and when d=7.0 mm, vax, =1.83 m/min. If min Ra=3.2 is required for the end product, then vax, =6.02 m/min is gotten for d=6.6 mm and vax, max max =7.05 m/min for d=7.0mm. The increase of vax has no notable influence on strain distribution along radial direction. The errors between the experimental and simulated height of the spiral spine-like ridges are below 8.0%.展开更多
The precipitation process of Ni-Cr-Al alloy with low Al content was studied at atomic scale based on the microscopicphase-field kinetic model coupled with elastic strain energy.The aim is to investigate the effect of ...The precipitation process of Ni-Cr-Al alloy with low Al content was studied at atomic scale based on the microscopicphase-field kinetic model coupled with elastic strain energy.The aim is to investigate the effect of elastic strain energy onprecipitation mechanism and morphological evolution of the alloy.The simulation results show that in the early stage of precipitation,D022 phase and L12 phase present irregular shape,and they randomly distribute in the matrix.With the progress of aging,L12 phaseand D022 phase change into the quadrate shape and their orientations become more obvious.In the later stage,L12 phase and D022phase present quadrate shape with round corner and align along the[100]and[010]directions,and highly preferential selectedmicrostructure is formed.The mechanism of early precipitation of L12 phase in Ni-17%Cr-7.5%Al(mole fraction)alloy is the mixedstyle of non-classical nucleation growth and spinodal decomposition and the D022 phase is the spinodal decomposition.Themechanisms of early precipitation of L12 phase and D022 phase in Ni-12.5%Cr-7.5%Al alloy are both the non-classical nucleationand growth.The coarsening process follows the rule of preferential selected coarsening.展开更多
Based on the results of triaxial compressive creep tests for five kinds of rock under the different stress loading,unloading and cycle-loading-unloading conditions,the creep deformation is not only a function of stres...Based on the results of triaxial compressive creep tests for five kinds of rock under the different stress loading,unloading and cycle-loading-unloading conditions,the creep deformation is not only a function of stress and time,but also it has the corresponding relations to the triaxial stress-strain curves of rock.The deformation properties of soften-strain,harden-strain and ideal plasticity presented by conventional triaxial compressive test curves under the different stress states were utilized,and the creep characteristics,the creep starting stress and the different entire creep process curves of rock were studied systematically according to creep experiment results,and the relations of the triaxial stress-strain curves to the creeping starting stress,the terminating curve,the different creep processes,and the different creep fracture properties were established.The relations presented in this paper were verified partially by the creep experiment results of five types of rock.展开更多
Compaction processes are one the most important par ts of powder forming technology. The main applications are focused on pieces for a utomotive, aeronautic, electric and electronic industries. The main goals of the c...Compaction processes are one the most important par ts of powder forming technology. The main applications are focused on pieces for a utomotive, aeronautic, electric and electronic industries. The main goals of the compaction processes are to obtain a compact with the geometrical requirements, without cracks, and with a uniform distribution of density. Design of such proc esses consist, essentially, in determine the sequence and relative displacements of die and punches in order to achieve such goals. A.B. Khoei presented a gener al framework for the finite element simulation of powder forming processes based on the following aspects; a large displacement formulation, centred on a total and updated Lagrangian formulation; an adaptive finite element strategy based on error estimates and automatic remeshing techniques; a cap model based on a hard ening rule in modelling of the highly non-linear behaviour of material; and the use of an efficient contact algorithm in the context of an interface element fo rmulation. In these references, the non-linear behaviour of powder was adequately desc ribed by the cap plasticity model. However, it suffers from a serious deficiency when the stress-point reaches a yield surface. In the flow theory of plasticit y, the transition from an elastic state to an elasto-plastic state appears more or less abruptly. For powder material it is very difficult to define the locati on of yield surface, because there is no distinct transition from elastic to ela stic-plastic behaviour. Results of experimental test on some hard met al powder show that the plastic effects were begun immediately upon loading. In such mater ials the domain of the yield surface would collapse to a point, so making the di rection of plastic increment indeterminate, because all directions are normal to a point. Thus, the classical plasticity theory cannot deal with such materials and an advanced constitutive theory is necessary. In the present paper, the constitutive equations of powder materials will be discussed via an endochronic theory of plasticity. This theory provides a unifi ed point of view to describe the elastic-plastic behaviour of material since it places no requirement for a yield surface and a ’loading function’ to disting uish between loading an unloading. Endochronic theory of plasticity has been app lied to a number of metallic materials, concrete and sand, but to the knowledge of authors, no numerical scheme of the model has been applied to powder material . In the present paper, a new approach is developed based on an endochronic rate independent, density-dependent plasticity model for describing the isothermal deformation behavior of metal powder at low homologous temperature. Although the concept of yield surface has not been explicitly assumed in endochronic theory, it is shown that the cone-cap plasticity yield surface (Fig.1), which is the m ost commonly used plasticity models for describing the behavior of powder materi al can be easily derived as a special case of the proposed endochronic theory. Fig.1 Trace of cone-cap yield function on the meridian pl ane for different relative density As large deformation is observed in powder compaction process, a hypoelastic-pl astic formulation is developed in the context of finite deformation plasticity. Constitutive equations are stated in unrotated frame of reference that greatly s implifies endochronic constitutive relation in finite plasticity. Constitutive e quations of the endochronic theory and their numerical integration are establish ed and procedures for determining material parameters of the model are demonstra ted. Finally, the numerical schemes are examined for efficiency in the model ling of a tip shaped component, as shown in Fig.2. Fig.2 A shaped tip component. a) Geometry, boundary conditio n and finite element mesh; b) density distribution at final stage of展开更多
咸蛋清是1种食品加工副产物,也是宝贵的蛋白质资源,利用耐盐细菌对其发酵降盐,可实现咸蛋清的回收再利用。以咸鸡蛋蛋壳为分离源,利用稀释划线法作耐盐菌种的分离纯化,结合革兰氏染色、生理生化特性检测、16S r RNA基因测序、系统进化...咸蛋清是1种食品加工副产物,也是宝贵的蛋白质资源,利用耐盐细菌对其发酵降盐,可实现咸蛋清的回收再利用。以咸鸡蛋蛋壳为分离源,利用稀释划线法作耐盐菌种的分离纯化,结合革兰氏染色、生理生化特性检测、16S r RNA基因测序、系统进化树构建等方法作菌株鉴定;利用溶血性、抗生素抗性、血浆凝固酶试验检测菌株安全性;利用单因素及正交试验法优化复合发酵咸蛋清工艺条件。结果表明:X140被鉴定为黄色植物杆菌(Plantibacter flavus),X29被鉴定为马胃葡萄球菌(Staphylococcus equorum),这2株食用安全的耐盐细菌均为革兰氏阳性菌,其在质量分数为8%NaCl的营养肉汤液体培养基中均表现出较强活力,可用于高盐食品发酵。以脱盐率为评价指标,通过单因素及正交试验法筛选得到最佳脱盐工艺参数:菌株添加量体积分数为3%、菌株复配体积比为1:2、发酵时间为40 h,在此工艺条件下,咸蛋清蛋白质保留率为95.12%,脱盐率为50.78%。展开更多
Structure evolution of an Al-Zn wrought alloy in remelting processing in thestrain induced melt activated (SIMA) serai-solid procedure was observed, and effects of factors, theremelting temperature, the holding time, ...Structure evolution of an Al-Zn wrought alloy in remelting processing in thestrain induced melt activated (SIMA) serai-solid procedure was observed, and effects of factors, theremelting temperature, the holding time, and the compression strain, on structures and grain sizesof the alloy were investigated. The results show that (1) the proper temperature of remelting is inthe range of 610 to 615℃; (2) the grain size in specimen with greater compression strain is smallerthan that with smaller compression strain in condition of the same remelting temperature andholding time, and the grain size in local area with great local equivalent strain is smaller thanthat with small one; (3) liquid occurs in form of cluster in matrix during remelting and itsquantity increases with remelting time increasing; liquid in specimen with great compression strainoccurs earlier than that with small one, and quantity of liquid in the center of specimen withgreater local equivalent strain is greater than that in the two ends of it; (4) distortion energyafter deforming in matrix of the alloy is the significant factor to activate melting of matrix atlocal area with great local equivalent strain.展开更多
基金Project(98009999200301) supported by the Ministry of Science and Technology of China
文摘A coupled thermal-mechanical model of the rotary swaging of pure magnesium was developed using the general finite-element software program MSC/Marc to visualize the effect of axial feeding velocity on the rotary swaging process. The radial displacement occurring in one pulse impact increases in proportion to axial feeding velocity (vax). When the other processing parameters are fixed, the surface roughness of the swaged bar increases with vax and is in parabolic relation with vax. There exists a minimum velocity vax, min below which the decrease of vax will no longer improve the surface roughness. Under the technological conditions of this simulation, when the finial diameter d=6.6 mm, vax, min=1.82 m/min, and when d=7.0 mm, vax, =1.83 m/min. If min Ra=3.2 is required for the end product, then vax, =6.02 m/min is gotten for d=6.6 mm and vax, max max =7.05 m/min for d=7.0mm. The increase of vax has no notable influence on strain distribution along radial direction. The errors between the experimental and simulated height of the spiral spine-like ridges are below 8.0%.
基金Projects(50671084,50071046)supported by the National Natural Science Foundation of ChinaProject(2002AA331051)supported by the National Hi-Tech Research Development Program of China
文摘The precipitation process of Ni-Cr-Al alloy with low Al content was studied at atomic scale based on the microscopicphase-field kinetic model coupled with elastic strain energy.The aim is to investigate the effect of elastic strain energy onprecipitation mechanism and morphological evolution of the alloy.The simulation results show that in the early stage of precipitation,D022 phase and L12 phase present irregular shape,and they randomly distribute in the matrix.With the progress of aging,L12 phaseand D022 phase change into the quadrate shape and their orientations become more obvious.In the later stage,L12 phase and D022phase present quadrate shape with round corner and align along the[100]and[010]directions,and highly preferential selectedmicrostructure is formed.The mechanism of early precipitation of L12 phase in Ni-17%Cr-7.5%Al(mole fraction)alloy is the mixedstyle of non-classical nucleation growth and spinodal decomposition and the D022 phase is the spinodal decomposition.Themechanisms of early precipitation of L12 phase and D022 phase in Ni-12.5%Cr-7.5%Al alloy are both the non-classical nucleationand growth.The coarsening process follows the rule of preferential selected coarsening.
基金Project(50774090) supported by the National Natural Science Foundation of China
文摘Based on the results of triaxial compressive creep tests for five kinds of rock under the different stress loading,unloading and cycle-loading-unloading conditions,the creep deformation is not only a function of stress and time,but also it has the corresponding relations to the triaxial stress-strain curves of rock.The deformation properties of soften-strain,harden-strain and ideal plasticity presented by conventional triaxial compressive test curves under the different stress states were utilized,and the creep characteristics,the creep starting stress and the different entire creep process curves of rock were studied systematically according to creep experiment results,and the relations of the triaxial stress-strain curves to the creeping starting stress,the terminating curve,the different creep processes,and the different creep fracture properties were established.The relations presented in this paper were verified partially by the creep experiment results of five types of rock.
文摘Compaction processes are one the most important par ts of powder forming technology. The main applications are focused on pieces for a utomotive, aeronautic, electric and electronic industries. The main goals of the compaction processes are to obtain a compact with the geometrical requirements, without cracks, and with a uniform distribution of density. Design of such proc esses consist, essentially, in determine the sequence and relative displacements of die and punches in order to achieve such goals. A.B. Khoei presented a gener al framework for the finite element simulation of powder forming processes based on the following aspects; a large displacement formulation, centred on a total and updated Lagrangian formulation; an adaptive finite element strategy based on error estimates and automatic remeshing techniques; a cap model based on a hard ening rule in modelling of the highly non-linear behaviour of material; and the use of an efficient contact algorithm in the context of an interface element fo rmulation. In these references, the non-linear behaviour of powder was adequately desc ribed by the cap plasticity model. However, it suffers from a serious deficiency when the stress-point reaches a yield surface. In the flow theory of plasticit y, the transition from an elastic state to an elasto-plastic state appears more or less abruptly. For powder material it is very difficult to define the locati on of yield surface, because there is no distinct transition from elastic to ela stic-plastic behaviour. Results of experimental test on some hard met al powder show that the plastic effects were begun immediately upon loading. In such mater ials the domain of the yield surface would collapse to a point, so making the di rection of plastic increment indeterminate, because all directions are normal to a point. Thus, the classical plasticity theory cannot deal with such materials and an advanced constitutive theory is necessary. In the present paper, the constitutive equations of powder materials will be discussed via an endochronic theory of plasticity. This theory provides a unifi ed point of view to describe the elastic-plastic behaviour of material since it places no requirement for a yield surface and a ’loading function’ to disting uish between loading an unloading. Endochronic theory of plasticity has been app lied to a number of metallic materials, concrete and sand, but to the knowledge of authors, no numerical scheme of the model has been applied to powder material . In the present paper, a new approach is developed based on an endochronic rate independent, density-dependent plasticity model for describing the isothermal deformation behavior of metal powder at low homologous temperature. Although the concept of yield surface has not been explicitly assumed in endochronic theory, it is shown that the cone-cap plasticity yield surface (Fig.1), which is the m ost commonly used plasticity models for describing the behavior of powder materi al can be easily derived as a special case of the proposed endochronic theory. Fig.1 Trace of cone-cap yield function on the meridian pl ane for different relative density As large deformation is observed in powder compaction process, a hypoelastic-pl astic formulation is developed in the context of finite deformation plasticity. Constitutive equations are stated in unrotated frame of reference that greatly s implifies endochronic constitutive relation in finite plasticity. Constitutive e quations of the endochronic theory and their numerical integration are establish ed and procedures for determining material parameters of the model are demonstra ted. Finally, the numerical schemes are examined for efficiency in the model ling of a tip shaped component, as shown in Fig.2. Fig.2 A shaped tip component. a) Geometry, boundary conditio n and finite element mesh; b) density distribution at final stage of
文摘Structure evolution of an Al-Zn wrought alloy in remelting processing in thestrain induced melt activated (SIMA) serai-solid procedure was observed, and effects of factors, theremelting temperature, the holding time, and the compression strain, on structures and grain sizesof the alloy were investigated. The results show that (1) the proper temperature of remelting is inthe range of 610 to 615℃; (2) the grain size in specimen with greater compression strain is smallerthan that with smaller compression strain in condition of the same remelting temperature andholding time, and the grain size in local area with great local equivalent strain is smaller thanthat with small one; (3) liquid occurs in form of cluster in matrix during remelting and itsquantity increases with remelting time increasing; liquid in specimen with great compression strainoccurs earlier than that with small one, and quantity of liquid in the center of specimen withgreater local equivalent strain is greater than that in the two ends of it; (4) distortion energyafter deforming in matrix of the alloy is the significant factor to activate melting of matrix atlocal area with great local equivalent strain.
