Based on simplified axisymmetrical forming model, a elasto-plastic FEM simulation system of multi-pass conventional spinning is developed. Taking the typical draw-spinning as the study object, and establishing reasona...Based on simplified axisymmetrical forming model, a elasto-plastic FEM simulation system of multi-pass conventional spinning is developed. Taking the typical draw-spinning as the study object, and establishing reasonable mechanics model, research on the first pass of spinning process is carried out with FEM system developed. The distributions of the stress and strain are obtained by three types of roller-trace curves: straight line, involute curves and quadratic curves. The results are as follows: (1) The values of equivalent stress and strain are the lowest under involute curve compared to other two curves, and they change relatively small and decrease with the increase of radius. The values of equivalent stress and strain is the highest under quadratic curves, and increase with the increase of radius. (2) The value of radial stress is smallest under involute curve, and is the largest under straight line. Value of radial stress is often used as the criterion of cracking limit, so its distribution laws can provide references for studying the condition of cracking in multi-pass conventional spinning under different roller-trace. (3) Tangential stress is compressive stress. Absolute value of tangential stress is the smallest under involute curve, and values of tangential stress are close between other two curves. The distribution laws of tangential stress can serve as a significant guide to research the critical condition of wrinkling in multi-pass conventional spinning under different roller-trace. (4) The reduction of thickness is the smallest under involute curve. The distribution of the thickness strain is very unequal under quadratic curves. The results obtained can provide references for selecting reasonable roller-trace in multi-pass conventional spinning.展开更多
Using a method of free energy minimization, this paper investigates the magnetization properties of a ferromagnetic （FM） monolayer and an FM/antiferromagnetic （AFM） bilayer under a stress field, respectively. It t...Using a method of free energy minimization, this paper investigates the magnetization properties of a ferromagnetic （FM） monolayer and an FM/antiferromagnetic （AFM） bilayer under a stress field, respectively. It then investigates the magnetoresistance （MR） of the spin-valve structure, which is built by an FM rnonolayer and an FM/AFM bilayer, and its dependence upon the applied stress field. The results show that under the stress field, the magnetization properties of the FM monolayer is obviously different from that of the FM/AFM bilayer, since the coupled AFM layer can obviously block the magnetization of the FM layer. This phenomenon makes the MR of the spin-valve structure become obvious. In detail, there are two behaviors for the MR of the spin-valve structure dependence upon the stress field distinguished by the coupling （FM coupling or AFM coupling） between the FM layer and the FM/AFM bilayer. Either behavior of the MR of the spin-valve structure depends on the stress field including its value and orientation. Based on these investigations, a perfect mechanical sensor at the nano-scale is suggested to be devised experimentally.展开更多
The application of computational fluid dynamics/computational solid method(CFD/CSM)on solving the aero-thermo-elastic problem of spinning rocket is introduced.Firstly,the aerodynamic coefficients of a rocket are calcu...The application of computational fluid dynamics/computational solid method(CFD/CSM)on solving the aero-thermo-elastic problem of spinning rocket is introduced.Firstly,the aerodynamic coefficients of a rocket are calculated,and the results are compared with the available experimental data,which verified the accuracy of the CFD output.Then,analysis is carried using ANSYS Workbench multi-physics coupling platform,which includes fluid,thermal,and structural solvers.The results show that spinning causes a significant effect on the deformations and stresses.Furthermore,thermal stresses due to high temperature at the rocket warhead and tail edges have a dominated effect,even more than those produced by aerodynamic forces.Consequently,this important outcome should be taken into consideration during the rocket design stages.展开更多
Based on the general solution given to a kind of linear tensor equations,the spin of a symmetric tensor is derived in an invariant form.The result is applied to find the spins of the left and the tight stretch tensors...Based on the general solution given to a kind of linear tensor equations,the spin of a symmetric tensor is derived in an invariant form.The result is applied to find the spins of the left and the tight stretch tensors and the relation among different rotation rate tensors has been discussed.According to work conjugacy,the relations between Cauchy stress and the stresses conjugate to Hill's generalized strains are obtained.Particularly,the logarithmic strain,its time rate and the conjugate stress have been discussed in de- tail.These results are important in modeling the constitutive relations for finite deformations in continuum me- chanics.展开更多
The residual stress distribution of Hastelloy C corrosion-resistant alloy tubes after power spinning was simulated with the elasto-plastic finite element method combining with the element birth and death technique, th...The residual stress distribution of Hastelloy C corrosion-resistant alloy tubes after power spinning was simulated with the elasto-plastic finite element method combining with the element birth and death technique, the influences of spinning parameters on the distribution of the residual stress were investigated in detail, and the formation mechanism of residual stress during tube spinning was discussed. Based on the calculation of the residual stress, the reasons for annealing cracks on the spun tube during interpass heat treatment were explored. The simulation results and the characteristics of annealing cracks show that the circumferential residual tensile stress is a main factor to cause the annealing cracks.展开更多
Objective To study the oxidative stress induced by consumption of mercury-contaminated rice in rats, and to assess the possible public health risk of mercury contamination in Wanshan mining area. Methods Sprague Dawle...Objective To study the oxidative stress induced by consumption of mercury-contaminated rice in rats, and to assess the possible public health risk of mercury contamination in Wanshan mining area. Methods Sprague Dawley rats were fed the mercury-contaminated rice produced from Wanshan area for 90 days. The antioxidant status and the free radicals in rat serum were evaluated. Results High mercury accumulation in organs of rats fed the mercury-contaminated rice confirmed the server pollution of mercury in Wanshan mining area. The intensity of electron spin resonance （ESR） signal increased by 87.38% in rats fed the rice from Wanshan compared with that in the control rats fed the rice from Shanghai, suggesting that chronic dietary consumption of rice from mercury mining area could induce an aggravation of free radicals. Feeding the mercury-contaminated rice was associated with significant decreases in the antioxidant enzymatic activities of superoxide dismutase （SOD） and glutathione peroxidase （GSH-Px） and concentration of serum nitric oxide （NO）, but it had no effect on serum nitric oxide synthase （NOS） activity. Feeding the mercury-contaminated rice raised the level of serum malonyldialdehyde （MDA）, indicating the occurrence of oxidative stress. Conclusion The long-term dietary consumption of mercury-contaminated rice induces the aggravation of free radicals and exerts oxidative stress.展开更多
We investigate the role of extended intrinsic mean spin tensor introduced in this work for turbulence modelling in a non-inertial frame of reference. It is described by the Euclidean group of transformations and, in p...We investigate the role of extended intrinsic mean spin tensor introduced in this work for turbulence modelling in a non-inertial frame of reference. It is described by the Euclidean group of transformations and, in particular, its significance and importance in the approach of the algebraic Reynolds stress modelling, such as in a nonlinear K-ε model. To this end and for illustration of the effect of extended intrinsic spin tensor on turbulence modelling, we examine several recently developed nonlinear K-ε models and compare their performance in predicting the homogeneous turbulent shear flow in a rotating frame of reference with LES data. Our results and analysis indicate that, only if the deficiencies of these models and the like be well understood and properly corrected, may in the near future, more sophisticated nonlinear K-ε models be developed to better predict complex turbulent flows in a non-inertial frame of reference.展开更多
文摘Based on simplified axisymmetrical forming model, a elasto-plastic FEM simulation system of multi-pass conventional spinning is developed. Taking the typical draw-spinning as the study object, and establishing reasonable mechanics model, research on the first pass of spinning process is carried out with FEM system developed. The distributions of the stress and strain are obtained by three types of roller-trace curves: straight line, involute curves and quadratic curves. The results are as follows: (1) The values of equivalent stress and strain are the lowest under involute curve compared to other two curves, and they change relatively small and decrease with the increase of radius. The values of equivalent stress and strain is the highest under quadratic curves, and increase with the increase of radius. (2) The value of radial stress is smallest under involute curve, and is the largest under straight line. Value of radial stress is often used as the criterion of cracking limit, so its distribution laws can provide references for studying the condition of cracking in multi-pass conventional spinning under different roller-trace. (3) Tangential stress is compressive stress. Absolute value of tangential stress is the smallest under involute curve, and values of tangential stress are close between other two curves. The distribution laws of tangential stress can serve as a significant guide to research the critical condition of wrinkling in multi-pass conventional spinning under different roller-trace. (4) The reduction of thickness is the smallest under involute curve. The distribution of the thickness strain is very unequal under quadratic curves. The results obtained can provide references for selecting reasonable roller-trace in multi-pass conventional spinning.
基金Project supported by the National Natural Science Foundation of China (Grant No 10347118)Natural Science Foundation of College of Jiangsu Province,China (Grant Nos 2006KJB140133 and 2007KJD140241)
文摘Using a method of free energy minimization, this paper investigates the magnetization properties of a ferromagnetic （FM） monolayer and an FM/antiferromagnetic （AFM） bilayer under a stress field, respectively. It then investigates the magnetoresistance （MR） of the spin-valve structure, which is built by an FM rnonolayer and an FM/AFM bilayer, and its dependence upon the applied stress field. The results show that under the stress field, the magnetization properties of the FM monolayer is obviously different from that of the FM/AFM bilayer, since the coupled AFM layer can obviously block the magnetization of the FM layer. This phenomenon makes the MR of the spin-valve structure become obvious. In detail, there are two behaviors for the MR of the spin-valve structure dependence upon the stress field distinguished by the coupling （FM coupling or AFM coupling） between the FM layer and the FM/AFM bilayer. Either behavior of the MR of the spin-valve structure depends on the stress field including its value and orientation. Based on these investigations, a perfect mechanical sensor at the nano-scale is suggested to be devised experimentally.
基金Supported by the National Natural Science Foundation of China(11102089)
文摘The application of computational fluid dynamics/computational solid method(CFD/CSM)on solving the aero-thermo-elastic problem of spinning rocket is introduced.Firstly,the aerodynamic coefficients of a rocket are calculated,and the results are compared with the available experimental data,which verified the accuracy of the CFD output.Then,analysis is carried using ANSYS Workbench multi-physics coupling platform,which includes fluid,thermal,and structural solvers.The results show that spinning causes a significant effect on the deformations and stresses.Furthermore,thermal stresses due to high temperature at the rocket warhead and tail edges have a dominated effect,even more than those produced by aerodynamic forces.Consequently,this important outcome should be taken into consideration during the rocket design stages.
基金The project is supported by the National Natural Science Foundation of Chinathe Chinese Academy of Sciences(No.87-52)
文摘Based on the general solution given to a kind of linear tensor equations,the spin of a symmetric tensor is derived in an invariant form.The result is applied to find the spins of the left and the tight stretch tensors and the relation among different rotation rate tensors has been discussed.According to work conjugacy,the relations between Cauchy stress and the stresses conjugate to Hill's generalized strains are obtained.Particularly,the logarithmic strain,its time rate and the conjugate stress have been discussed in de- tail.These results are important in modeling the constitutive relations for finite deformations in continuum me- chanics.
基金the National Natural Science Foundation of China(No.59995444).
文摘The residual stress distribution of Hastelloy C corrosion-resistant alloy tubes after power spinning was simulated with the elasto-plastic finite element method combining with the element birth and death technique, the influences of spinning parameters on the distribution of the residual stress were investigated in detail, and the formation mechanism of residual stress during tube spinning was discussed. Based on the calculation of the residual stress, the reasons for annealing cracks on the spun tube during interpass heat treatment were explored. The simulation results and the characteristics of annealing cracks show that the circumferential residual tensile stress is a main factor to cause the annealing cracks.
基金This work was supported by National Natural Science Foundation of China (No. 20607014)
文摘Objective To study the oxidative stress induced by consumption of mercury-contaminated rice in rats, and to assess the possible public health risk of mercury contamination in Wanshan mining area. Methods Sprague Dawley rats were fed the mercury-contaminated rice produced from Wanshan area for 90 days. The antioxidant status and the free radicals in rat serum were evaluated. Results High mercury accumulation in organs of rats fed the mercury-contaminated rice confirmed the server pollution of mercury in Wanshan mining area. The intensity of electron spin resonance （ESR） signal increased by 87.38% in rats fed the rice from Wanshan compared with that in the control rats fed the rice from Shanghai, suggesting that chronic dietary consumption of rice from mercury mining area could induce an aggravation of free radicals. Feeding the mercury-contaminated rice was associated with significant decreases in the antioxidant enzymatic activities of superoxide dismutase （SOD） and glutathione peroxidase （GSH-Px） and concentration of serum nitric oxide （NO）, but it had no effect on serum nitric oxide synthase （NOS） activity. Feeding the mercury-contaminated rice raised the level of serum malonyldialdehyde （MDA）, indicating the occurrence of oxidative stress. Conclusion The long-term dietary consumption of mercury-contaminated rice induces the aggravation of free radicals and exerts oxidative stress.
文摘We investigate the role of extended intrinsic mean spin tensor introduced in this work for turbulence modelling in a non-inertial frame of reference. It is described by the Euclidean group of transformations and, in particular, its significance and importance in the approach of the algebraic Reynolds stress modelling, such as in a nonlinear K-ε model. To this end and for illustration of the effect of extended intrinsic spin tensor on turbulence modelling, we examine several recently developed nonlinear K-ε models and compare their performance in predicting the homogeneous turbulent shear flow in a rotating frame of reference with LES data. Our results and analysis indicate that, only if the deficiencies of these models and the like be well understood and properly corrected, may in the near future, more sophisticated nonlinear K-ε models be developed to better predict complex turbulent flows in a non-inertial frame of reference.
