The present paper is devoted to developing a new numerical simulation method for the analysis of viscous pressure forming （VPF）, which is a sheet flexible-die forming （FDF） process. The pressure-carrying medium us...The present paper is devoted to developing a new numerical simulation method for the analysis of viscous pressure forming （VPF）, which is a sheet flexible-die forming （FDF） process. The pressure-carrying medium used in VPF is one kind of semisolid, flowable and viscous material and its deformation behavior can be described by the visco-elastoplastic constitutive model. A sectional finite element model for the coupled deformation analysis between the viscoelastoplastic pressure-carrying medium and the elastoplastic sheet metal is proposed. The resolution of the Updated Lagrangian （UL） formulation is based on a static explicit approach. The frictional contact between sheet metal and visco-elastoplastic pressure-carrying medium is treated by the penalty function method. Coupled deformation between sheet metal and visco-elastoplastic pressure-carrying medium with large slip is analyzed to validate the developed algorithm. Finally, the viscous pressure bulging （VPB） process of DC06 sheet metal is simulated. Good agreement between numerical simulation results and experimental measurements shows the validity of the developed algorithm.展开更多
The hydroforming experiment of aluminum tubular part with rectangular section was carried out to investigate influence of axial feeding on thickness distribution and calibration pressure of the corner.Thickness distri...The hydroforming experiment of aluminum tubular part with rectangular section was carried out to investigate influence of axial feeding on thickness distribution and calibration pressure of the corner.Thickness distribution and relation between corner radius and internal pressure were analyzed.The influence of lubricant was discussed.Microstructure and hardness of different region were observed.It is shown that thickness reduction in the transition region between the corner and center region is the biggest.Friction condition has influence both on the thickness distribution and calibration pressure of the corner.As the increase of the axial feeding,the calibration pressure is decreased.There is only little change for the microstructure,but the hardness is increased by 23.3% for the transition region.展开更多
The aim of this study was to compare mandibular form （i.e., size and shape） between patients with agenesis of the lower second premolar （P2） and a control group with no agenesis. Three hypotheses were tested： （H...The aim of this study was to compare mandibular form （i.e., size and shape） between patients with agenesis of the lower second premolar （P2） and a control group with no agenesis. Three hypotheses were tested： （H1） agenesis causes a change in mandibular morphology because of inadequate alveolar ridge development in the area of the missing tooth （mandibular plasticity）; （H2） agenesis is caused by spatial limitations within the mandible （dental plasticity）; and （H3） common genetic/ epigenetic factors cause agenesis and affect mandibular form （pleiotropy）. A geometric morphometric analysis was applied to cross-sectional images of computed tomography （CT） scans of three matched groups （n= 50 each）： （1） regularly erupted P2; （2） agenesis of P2 and the primary second molar in situ; and （3） agenesis of P2 and the primary second molar missing for 〉3 months. Cross-sections of the three areas of interest （first premolar, P2, first molar） were digitized with 23 landmarks and superimposed by a generalized Procrustes analysis. On average, the mandibular cross-sections were narrower and shorter in patients with P2 agenesis compared with that in the control group. Both agenesis groups featured a pronounced submandibular fossa. These differences extended at least one tooth beyond the agenesis-affected region. Taken together with the large interindividual variation that resulted in massively overlapping group distributions, these findings support genetic and/or epigenetic pleiotropy （H3） as the most likely origin of the observed covariation between mandibular form and odontogenesis. Clinically, reduced dimensions and greater variability of mandibular form, as well as a pronounced submandibular fossa, should be expected during the treatment planning of patients with P2 agenesis.展开更多
The finite strip method in structural analysis has been extended, and elastic-plastic large deformation spline finite strip method based on the Updated-Lagrange method (U. L. method) was established to simulate roll f...The finite strip method in structural analysis has been extended, and elastic-plastic large deformation spline finite strip method based on the Updated-Lagrange method (U. L. method) was established to simulate roll forming process of channel section with outer edge. The deformation characteristics of strip was analyzed, and the three-dimensional displacement field, strain field and stress field of deformed strip were got. The calculation example proves that the peak transverse pressing membrane strain is on the corner part of the deformed strip, and the peak longitudinal stretching strain is on the outer edge part of the deformed strip in front of rolls. In addition, the transverse deformation of the deformed strip is principal, and the longitudinal deformation is small.展开更多
With the rapid development of microscale cellular structures, the small-diameter cold-formed welded stainless steel tubes have recently been used for creating the metallic lat- tice topologies with high mechanical pro...With the rapid development of microscale cellular structures, the small-diameter cold-formed welded stainless steel tubes have recently been used for creating the metallic lat- tice topologies with high mechanical properties. In this paper, to obtain the accurate material properties of the circular hollow section （CHS） under pure compression, a series of concentric compression tests are conducted on the millimeter-scale cold-formed 304 stainless steel circu- lar tubular stub columns after exposure to a vacuum brazing process. The tests cover a total of 18 small-diameter stub tubes with measured thickness-to-diameter ratios （t/D） from 0.023 to 0.201. A generalized three-stage nominal stress-strain model is developed for describing the compressive behavior of the post-brazing CHSs over the full strain range. This mechanical model is especially applicable to computer code implementation. Hence, an interactive computer pro- gram is developed to simultaneously optimize three strain hardening exponents （n1, n2, n3） in the expression of the model to produce the stress-strain curve capable of accurately replicating the test data. To further reduce the number of the model and material parameters on which this model depends, this paper also develops five expressions for determining the 2.5% proof stress （ap2）, n2, the ultimate compressive strength （σp3）, n3, and the ultimate plastic strain （p3%） for given experimental values of three basic material parameters （E0, σ0.01, σ0.2）. These expressions are validated to he effective for the CHSs with t/D 〉_ 0.027. The analytically predicted full-range stress-strain curves have generally shown close agreement with the ones obtained experimentally.展开更多
We estimate the electromagnetic form factor of the transverse part of cross section σTand provide a correction for the electromagnetic form factor of the longitudinal component of cross section σLfor the charged pio...We estimate the electromagnetic form factor of the transverse part of cross section σTand provide a correction for the electromagnetic form factor of the longitudinal component of cross section σLfor the charged pion within the frame work of hadronic operator. To achieve this, we consider a slightly deformed curve deviating from a straight line and construct a set of differential equations by comparing them to the equation determining charged pion wave function in a straight line case. By solving these equations, we employ the Fourier transform of these wave functions.展开更多
A novel forming method of nickel based super-alloy thin-walled part with variable diameter sections was proposed by using inner and outer pressure with the visco-elasto-plastic pressure-carrying medium at room tempera...A novel forming method of nickel based super-alloy thin-walled part with variable diameter sections was proposed by using inner and outer pressure with the visco-elasto-plastic pressure-carrying medium at room temperature,and the principle of the method was provided.Experiments and FE simulations were carried out to analyze the deformation characteristics for the part with larger variable diameter ratio(35%).The results show that visco-elasto-plastic pressure-carrying medium can meet the requirements of the room-temperature deformation condition for nickel based super-alloy sheet.The inner and outer pressure forming with the visco-elasto-plastic pressure-carrying medium can meet the requirements of dimensional accuracy for the thin-walled part with variable diameter sections.The thinning of wall-thickness is less than 4%.This method provides a new approach for near-net shape forming of nickel based super-alloy thin-walled parts with variable diameter sections.展开更多
巷道断面成形是煤矿掘进过程中的重要工序,但目前的巷道断面成形作业多为人工控制掘进机进行往复式截割,制约了煤矿掘进工作面的智能化发展。为此,针对断面成形轨迹规划未考虑煤岩特征、优化目标单一的问题,提出了一种基于改进灰狼优化(...巷道断面成形是煤矿掘进过程中的重要工序,但目前的巷道断面成形作业多为人工控制掘进机进行往复式截割,制约了煤矿掘进工作面的智能化发展。为此,针对断面成形轨迹规划未考虑煤岩特征、优化目标单一的问题,提出了一种基于改进灰狼优化(grey wolf optimizer, GWO)算法的掘进机断面成形轨迹规划方法。首先,根据夹矸位置将待截割断面环境分为4种情况,对相应断面进行栅格化处理并建立栅格地图,同时采用二值膨胀法对不规则夹矸进行膨胀化处理。然后,对GWO算法进行了改进,以提升其寻优性能和收敛速度。接着,开展了仿真实验,利用改进GWO算法实现了4种环境下掘进机断面成形轨迹的规划。最后,利用掘进机样机开展了断面截割实验。仿真结果表明:相较于传统的GWO算法,改进GWO算法的收敛速度更快且收敛精度更高;在4种断面环境下,基于改进GWO算法规划的断面成形轨迹长度最短,欠挖面积最小,转向次数最少,更容易实现高精度、高效率的轨迹跟踪控制,保证了巷道断面的成形质量。实验结果表明,基于改进GWO算法规划的断面成形轨迹既能提高掘进机的截割效率,又能满足巷道断面成形的质量要求。研究结果可为煤矿井下智能掘进技术的发展提供新的思路和方法。展开更多
This paper is concerned with the L2 harmonic forms of a complete noncompact Riemannian manifold, i.e. If M has a pole Q, let 0 < p <p<n, and assume the radial section curvatures satisfy on M ?{Q}, where then ...This paper is concerned with the L2 harmonic forms of a complete noncompact Riemannian manifold, i.e. If M has a pole Q, let 0 < p <p<n, and assume the radial section curvatures satisfy on M ?{Q}, where then Hp = {0}. If M has a soul, then similar result is obtained.展开更多
Theinvestigation of physicometallurgicalphenomena forthe CC formingof WCP/ Fe Ccom posites wasperformed. Resultsshow that underthe patentcondition, WCP/ Fe Ccomposite surfacelayerof16 20 m m heavycross sectio...Theinvestigation of physicometallurgicalphenomena forthe CC formingof WCP/ Fe Ccom posites wasperformed. Resultsshow that underthe patentcondition, WCP/ Fe Ccomposite surfacelayerof16 20 m m heavycross sectioncan beacquiredintheoutsideofa hollow cylin der. The surface of CTC particlescould be partially dissolved by Fe containing melt. Thefineshortstick like WCcrystallitesarein situseparated neartothesurfaceof CTC particles.Far from the CTC particles,someseparated, finetungsten carbidecrystallitesand Fe, W,Mo and Cretc. containing web composite carbides, are distributed on the matrix of WCP/ Fe Ccomposite. Fe Calloy matrix of the hollow composite cylinder is alloyed in differenthigh levels.展开更多
Let x ： M→S^n＋1 be a hypersurface in the （n ＋ 1）-dimensional unit sphere S^n＋1 without umbilic point. The Mobius invariants of x under the Mobius transformation group of S^n＋1 are Mobius metric, Mobius form, M...Let x ： M→S^n＋1 be a hypersurface in the （n ＋ 1）-dimensional unit sphere S^n＋1 without umbilic point. The Mobius invariants of x under the Mobius transformation group of S^n＋1 are Mobius metric, Mobius form, Mobius second fundamental form and Blaschke tensor. In this paper, we prove the following theorem： Let x ： M→S^n＋1 （n≥2） be an umbilic free hypersurface in S^n＋1 with nonnegative Mobius sectional curvature and with vanishing Mobius form. Then x is locally Mobius equivalent to one of the following hypersurfaces： （i） the torus S^k（a） × S^n-k（√1- a^2） with 1 ≤ k ≤ n - 1; （ii） the pre-image of the stereographic projection of the standard cylinder S^k × R^n-k belong to R^n＋1 with 1 ≤ k ≤ n- 1; （iii） the pre-image of the stereographic projection of the Cone in R^n＋1 ： -↑x（u, v, t） = （tu, tv）, where （u,v, t）∈S^k（a） × S^n-k-1（ √1-a^2）× R^＋.展开更多
Analyzing the mass of behind-armor debris (BAD) generated by Rolled Homogeneous Armor (RHA) subjected to normal penetration of variable cross-section Explosively Formed Projectile (EFP) is the purpose of this paper. S...Analyzing the mass of behind-armor debris (BAD) generated by Rolled Homogeneous Armor (RHA) subjected to normal penetration of variable cross-section Explosively Formed Projectile (EFP) is the purpose of this paper. So theoretical analysis, numerical simulation and experimental data are combined to analyze the influence of variable cross-section characteristic on the time history of crater radius. Moreover the relationships between time history of crater radius (as well as mass of BAD) and the thickness of RHA (from 30mm to 70 mm) and the impact velocity of EFP (1650 m/s to 1860 m/s) are also investigated. The results indicate that: 1) being compared to the variable cross-section characteristic is ignored, the theoretical time history of crater radius is in better agreement with the simulation results when the variable cross-section characteristic is considered;2) being compared to the other three conditions of plug, the theoretical mass of BAD is in the best agreement with the simulation results when the shape of plug is frustum of a cone and the angle between generatrix and bottom is 45- and the axial length of mushroom is considered.展开更多
基金supported by the National Natural Science Foundation of China (No. 50275035)
文摘The present paper is devoted to developing a new numerical simulation method for the analysis of viscous pressure forming （VPF）, which is a sheet flexible-die forming （FDF） process. The pressure-carrying medium used in VPF is one kind of semisolid, flowable and viscous material and its deformation behavior can be described by the visco-elastoplastic constitutive model. A sectional finite element model for the coupled deformation analysis between the viscoelastoplastic pressure-carrying medium and the elastoplastic sheet metal is proposed. The resolution of the Updated Lagrangian （UL） formulation is based on a static explicit approach. The frictional contact between sheet metal and visco-elastoplastic pressure-carrying medium is treated by the penalty function method. Coupled deformation between sheet metal and visco-elastoplastic pressure-carrying medium with large slip is analyzed to validate the developed algorithm. Finally, the viscous pressure bulging （VPB） process of DC06 sheet metal is simulated. Good agreement between numerical simulation results and experimental measurements shows the validity of the developed algorithm.
基金Funded by the National Natural Science Foundation of China(50525516)
文摘The hydroforming experiment of aluminum tubular part with rectangular section was carried out to investigate influence of axial feeding on thickness distribution and calibration pressure of the corner.Thickness distribution and relation between corner radius and internal pressure were analyzed.The influence of lubricant was discussed.Microstructure and hardness of different region were observed.It is shown that thickness reduction in the transition region between the corner and center region is the biggest.Friction condition has influence both on the thickness distribution and calibration pressure of the corner.As the increase of the axial feeding,the calibration pressure is decreased.There is only little change for the microstructure,but the hardness is increased by 23.3% for the transition region.
文摘The aim of this study was to compare mandibular form （i.e., size and shape） between patients with agenesis of the lower second premolar （P2） and a control group with no agenesis. Three hypotheses were tested： （H1） agenesis causes a change in mandibular morphology because of inadequate alveolar ridge development in the area of the missing tooth （mandibular plasticity）; （H2） agenesis is caused by spatial limitations within the mandible （dental plasticity）; and （H3） common genetic/ epigenetic factors cause agenesis and affect mandibular form （pleiotropy）. A geometric morphometric analysis was applied to cross-sectional images of computed tomography （CT） scans of three matched groups （n= 50 each）： （1） regularly erupted P2; （2） agenesis of P2 and the primary second molar in situ; and （3） agenesis of P2 and the primary second molar missing for 〉3 months. Cross-sections of the three areas of interest （first premolar, P2, first molar） were digitized with 23 landmarks and superimposed by a generalized Procrustes analysis. On average, the mandibular cross-sections were narrower and shorter in patients with P2 agenesis compared with that in the control group. Both agenesis groups featured a pronounced submandibular fossa. These differences extended at least one tooth beyond the agenesis-affected region. Taken together with the large interindividual variation that resulted in massively overlapping group distributions, these findings support genetic and/or epigenetic pleiotropy （H3） as the most likely origin of the observed covariation between mandibular form and odontogenesis. Clinically, reduced dimensions and greater variability of mandibular form, as well as a pronounced submandibular fossa, should be expected during the treatment planning of patients with P2 agenesis.
文摘The finite strip method in structural analysis has been extended, and elastic-plastic large deformation spline finite strip method based on the Updated-Lagrange method (U. L. method) was established to simulate roll forming process of channel section with outer edge. The deformation characteristics of strip was analyzed, and the three-dimensional displacement field, strain field and stress field of deformed strip were got. The calculation example proves that the peak transverse pressing membrane strain is on the corner part of the deformed strip, and the peak longitudinal stretching strain is on the outer edge part of the deformed strip in front of rolls. In addition, the transverse deformation of the deformed strip is principal, and the longitudinal deformation is small.
基金The work was supported by the National Natural Science Foundation of China under Grant Nos. 11432004 and 11421091.
文摘With the rapid development of microscale cellular structures, the small-diameter cold-formed welded stainless steel tubes have recently been used for creating the metallic lat- tice topologies with high mechanical properties. In this paper, to obtain the accurate material properties of the circular hollow section （CHS） under pure compression, a series of concentric compression tests are conducted on the millimeter-scale cold-formed 304 stainless steel circu- lar tubular stub columns after exposure to a vacuum brazing process. The tests cover a total of 18 small-diameter stub tubes with measured thickness-to-diameter ratios （t/D） from 0.023 to 0.201. A generalized three-stage nominal stress-strain model is developed for describing the compressive behavior of the post-brazing CHSs over the full strain range. This mechanical model is especially applicable to computer code implementation. Hence, an interactive computer pro- gram is developed to simultaneously optimize three strain hardening exponents （n1, n2, n3） in the expression of the model to produce the stress-strain curve capable of accurately replicating the test data. To further reduce the number of the model and material parameters on which this model depends, this paper also develops five expressions for determining the 2.5% proof stress （ap2）, n2, the ultimate compressive strength （σp3）, n3, and the ultimate plastic strain （p3%） for given experimental values of three basic material parameters （E0, σ0.01, σ0.2）. These expressions are validated to he effective for the CHSs with t/D 〉_ 0.027. The analytically predicted full-range stress-strain curves have generally shown close agreement with the ones obtained experimentally.
文摘We estimate the electromagnetic form factor of the transverse part of cross section σTand provide a correction for the electromagnetic form factor of the longitudinal component of cross section σLfor the charged pion within the frame work of hadronic operator. To achieve this, we consider a slightly deformed curve deviating from a straight line and construct a set of differential equations by comparing them to the equation determining charged pion wave function in a straight line case. By solving these equations, we employ the Fourier transform of these wave functions.
文摘A novel forming method of nickel based super-alloy thin-walled part with variable diameter sections was proposed by using inner and outer pressure with the visco-elasto-plastic pressure-carrying medium at room temperature,and the principle of the method was provided.Experiments and FE simulations were carried out to analyze the deformation characteristics for the part with larger variable diameter ratio(35%).The results show that visco-elasto-plastic pressure-carrying medium can meet the requirements of the room-temperature deformation condition for nickel based super-alloy sheet.The inner and outer pressure forming with the visco-elasto-plastic pressure-carrying medium can meet the requirements of dimensional accuracy for the thin-walled part with variable diameter sections.The thinning of wall-thickness is less than 4%.This method provides a new approach for near-net shape forming of nickel based super-alloy thin-walled parts with variable diameter sections.
文摘巷道断面成形是煤矿掘进过程中的重要工序,但目前的巷道断面成形作业多为人工控制掘进机进行往复式截割,制约了煤矿掘进工作面的智能化发展。为此,针对断面成形轨迹规划未考虑煤岩特征、优化目标单一的问题,提出了一种基于改进灰狼优化(grey wolf optimizer, GWO)算法的掘进机断面成形轨迹规划方法。首先,根据夹矸位置将待截割断面环境分为4种情况,对相应断面进行栅格化处理并建立栅格地图,同时采用二值膨胀法对不规则夹矸进行膨胀化处理。然后,对GWO算法进行了改进,以提升其寻优性能和收敛速度。接着,开展了仿真实验,利用改进GWO算法实现了4种环境下掘进机断面成形轨迹的规划。最后,利用掘进机样机开展了断面截割实验。仿真结果表明:相较于传统的GWO算法,改进GWO算法的收敛速度更快且收敛精度更高;在4种断面环境下,基于改进GWO算法规划的断面成形轨迹长度最短,欠挖面积最小,转向次数最少,更容易实现高精度、高效率的轨迹跟踪控制,保证了巷道断面的成形质量。实验结果表明,基于改进GWO算法规划的断面成形轨迹既能提高掘进机的截割效率,又能满足巷道断面成形的质量要求。研究结果可为煤矿井下智能掘进技术的发展提供新的思路和方法。
文摘This paper is concerned with the L2 harmonic forms of a complete noncompact Riemannian manifold, i.e. If M has a pole Q, let 0 < p <p<n, and assume the radial section curvatures satisfy on M ?{Q}, where then Hp = {0}. If M has a soul, then similar result is obtained.
文摘Theinvestigation of physicometallurgicalphenomena forthe CC formingof WCP/ Fe Ccom posites wasperformed. Resultsshow that underthe patentcondition, WCP/ Fe Ccomposite surfacelayerof16 20 m m heavycross sectioncan beacquiredintheoutsideofa hollow cylin der. The surface of CTC particlescould be partially dissolved by Fe containing melt. Thefineshortstick like WCcrystallitesarein situseparated neartothesurfaceof CTC particles.Far from the CTC particles,someseparated, finetungsten carbidecrystallitesand Fe, W,Mo and Cretc. containing web composite carbides, are distributed on the matrix of WCP/ Fe Ccomposite. Fe Calloy matrix of the hollow composite cylinder is alloyed in differenthigh levels.
文摘Let x ： M→S^n＋1 be a hypersurface in the （n ＋ 1）-dimensional unit sphere S^n＋1 without umbilic point. The Mobius invariants of x under the Mobius transformation group of S^n＋1 are Mobius metric, Mobius form, Mobius second fundamental form and Blaschke tensor. In this paper, we prove the following theorem： Let x ： M→S^n＋1 （n≥2） be an umbilic free hypersurface in S^n＋1 with nonnegative Mobius sectional curvature and with vanishing Mobius form. Then x is locally Mobius equivalent to one of the following hypersurfaces： （i） the torus S^k（a） × S^n-k（√1- a^2） with 1 ≤ k ≤ n - 1; （ii） the pre-image of the stereographic projection of the standard cylinder S^k × R^n-k belong to R^n＋1 with 1 ≤ k ≤ n- 1; （iii） the pre-image of the stereographic projection of the Cone in R^n＋1 ： -↑x（u, v, t） = （tu, tv）, where （u,v, t）∈S^k（a） × S^n-k-1（ √1-a^2）× R^＋.
基金financially supported by the National Natural Science Foundation of China(Grant No.11372136)
文摘Analyzing the mass of behind-armor debris (BAD) generated by Rolled Homogeneous Armor (RHA) subjected to normal penetration of variable cross-section Explosively Formed Projectile (EFP) is the purpose of this paper. So theoretical analysis, numerical simulation and experimental data are combined to analyze the influence of variable cross-section characteristic on the time history of crater radius. Moreover the relationships between time history of crater radius (as well as mass of BAD) and the thickness of RHA (from 30mm to 70 mm) and the impact velocity of EFP (1650 m/s to 1860 m/s) are also investigated. The results indicate that: 1) being compared to the variable cross-section characteristic is ignored, the theoretical time history of crater radius is in better agreement with the simulation results when the variable cross-section characteristic is considered;2) being compared to the other three conditions of plug, the theoretical mass of BAD is in the best agreement with the simulation results when the shape of plug is frustum of a cone and the angle between generatrix and bottom is 45- and the axial length of mushroom is considered.
