The incremental constitutive relation and governing equations with combined stresses for phase transition wave propagation in a thin-walled tube are established based on the phase transition criterion considering both...The incremental constitutive relation and governing equations with combined stresses for phase transition wave propagation in a thin-walled tube are established based on the phase transition criterion considering both the hydrostatic pressure and the deviatoric stress. It is found that the centers of the initial and subsequent phase transition ellipses are shifted along the sigma-axis in the sigma tau-plane due to the tension-compression asymmetry induced by the hydrostatic pressure. The wave solution offers the 'fast' and 'slow' phase transition waves under combined longitudinal and torsional stresses in the phase transition region. The results show some new stress paths and wave structures in a thin-walled tube with phase transition, differing from those of conventional elastic-plastic materials.展开更多
An in-depth analysis of propagation characteristics ofelasto-plastic combined stress waves in circular thin-walled tubeshas been made. In obtaining the simple-wave solution, however, mostresearches have ignored the in...An in-depth analysis of propagation characteristics ofelasto-plastic combined stress waves in circular thin-walled tubeshas been made. In obtaining the simple-wave solution, however, mostresearches have ignored the influence of the circumferential stressrelated to the radial inertial ef- fect in the tubes. In this paperthe incremental elasto-plastic constitutive relations which areconve- nient for dynamic numerical analysis are adopted, and thefinite-difference method is used to study the evolution adpropagation of elasto-plastic combined stress waves in a thin-walledtube with the radial inertial effect of the tube considered. Thecalculation results are compared with those obtained when the radialinertial effect is not considered. The calculation results show thatthe radial inertial effect of a tube has a fairly great influence onthe propagation of elasto-plastic combined stress waves.展开更多
An experimental investigation was carried out to study the energy absorption characteristics of thin-walled square tubes subjected to dynamic crushing by impact loading to develop the optimum structural members. Here,...An experimental investigation was carried out to study the energy absorption characteristics of thin-walled square tubes subjected to dynamic crushing by impact loading to develop the optimum structural members. Here, the controller is introduced to improve and control the absorbed energy of thin-walled square tubes in this paper. When the controller were used, the experimental results of crushing of square tubes controlled by the controller's elements showed a good candidate for a controllable energy absorption capability in impact crushing.展开更多
Cross-section deformation is one of important factors affecting the quality of tube formation, and the tube's capability of transporting liquid and gas will be reduced because of the cross-section ellipse deformation...Cross-section deformation is one of important factors affecting the quality of tube formation, and the tube's capability of transporting liquid and gas will be reduced because of the cross-section ellipse deformation due to the effect of shear load in plastic bending process. When the tube is bent, the extrados-wall bears the tension stress and the intrados-wall bears the compression stress, synchronously the cross-section is affected by the circumferential stress. According to the above, the distribution function and curve of tangential stress can be obtained according to force balance differential equations on circumferential direction and Trasca rule. Subsequently the real state and virtual state moment equations were established, a new method was presented adopting the virtual principle of deformation system to calculate the x-axis and y-axis displacement of arbitrary point on cross-section. So the major and minor axes of deformed cross-section can be calculated according to the displacements of each point, and the variety value of major and minor axes will be obtained further. Finally the theoretical calculating result is compared with NC tube rotary-bending experiment results to verify the rationality of theoretical analysis, and the cross-section deformation rule of thin-walled tube can be received.展开更多
The thin-walled tube flexure(TWTF) hinges have important potential application value in the deployment mechanisms of satellite and solar array, but the optimal design of the TWTF hinges haven't been completely solv...The thin-walled tube flexure(TWTF) hinges have important potential application value in the deployment mechanisms of satellite and solar array, but the optimal design of the TWTF hinges haven't been completely solved, which restricts their applications. An optimal design method for the qusai-static folding and deploying of TWTF hinges with double slots is presented based on the response surface theory. Firstly, the full factorial method is employed to design of the experiments. Then, the finite element models of the TWTF hinges with double slots are constructed to simulate the qusai-static folding and deploying non-linear analysis. What's more, the mathematical model of the TWTF flexure hinge quasi-static folding and deploying properties are derived by the response surface method. Considering of small mass and high stability, the peak moment of quasi-static folding and deploying as well as the lightless are set as the objectives to get the optimal performances. The relative errors of the objectives between the optimal design results and the FE analysis results are less than 7%, which demonstrates the precision of the surrogate models. Lastly, the parameter study shows that both the slots length and the slots width both have significant effects to the peak moment of quasi-static folding and deploying of TWTF hinges with double slots. However, the maximum Mises stress of quasi-static folding is more sensitive to the slots length than the slots width. The proposed research can be applied to optimize other thin-walled flexure hinges under quasi-static folding and deploying, which is of great importance to design of flexure hinges with high stability and low stress.展开更多
High frequency shock load is often generated during pyrotechnic device working, which is detrimental to spacecraft structures and electric devices. Therefore, it is valuable to reduce the shock load in pyrotechnic dev...High frequency shock load is often generated during pyrotechnic device working, which is detrimental to spacecraft structures and electric devices. Therefore, it is valuable to reduce the shock load in pyrotechnic device design. Actually, there are several ways to decrease pyroshock loads, such as reduction of powder,installation of buffering structure, insulation of damageable devices, and so on. Considered assuring the function of pyrotechnic device and minimum of structure modification, shock absorbing structure is more propitious to be introduced in pyrotechnic device. In this paper, based on the method of thinwalled metal tube diameter-expanding, a thin-walled tube shock buffering structure was designed on a separate bolt. Built on the simplified structure of a separate bolt, the model of cone piston impacting thin-walled tube absorber was established, and the thin-walled tube shock absorbing characteristics and the relation between cone angles and absorber performance were analyzed. The results showed that the change of buffering force of thin-walled tube could be divided into four phases, and each phase was correspondent to the cone piston structure. In addition, as the cone angle increases, the max shock acceleration changes in the style of decrease-increase-decrease-increase, which is the result of coupled effects of cone piston max enter depth, buffering force and energy loss. In short, these results could establish the relationships between thin-walled tube absorbing performance and its structure, which is of significance to develop low-shock pyrotechnic device.展开更多
Springback is one of important factors influencing the forming quality of numerical control (NC) bending of thin-walled tube. In this paper, a numerical-analytic method for springback angle prediction of the process...Springback is one of important factors influencing the forming quality of numerical control (NC) bending of thin-walled tube. In this paper, a numerical-analytic method for springback angle prediction of the process was put forward. The method is based on springback angle model derived using analytic method and simulation results from three-dimensional (3D) rigid-plastic finite element method (FEM). The method is validated through comparison with experimental results. The features of the method are as follows: (1) The method is high in efficiency because it combines advantages of rigid-plastic FEM and analytic method. (2) The method is satisfactory in accuracy, since the field variables used in the model is resulting from 3D rigid-plastic FEM solution, and the effects both of axial force and strain neutral axis shift have been included. (3) Research on multi-factor effects can be carried out using the method due to its advantage inheriting from rigid-plastic FEM. The method described here is also of general significance to other bending processes.展开更多
This study proposed a prediction formula for the torsional strength enabling to reflect the tensile strength of ultra high performance concrete (UHPC) beams based upon the thin-walled tube theory. The remarkable ducti...This study proposed a prediction formula for the torsional strength enabling to reflect the tensile strength of ultra high performance concrete (UHPC) beams based upon the thin-walled tube theory. The remarkable ductile behavior of UHPC can also be attributed to the steel fiber reinforcement. This feature must be considered to provide rational explanation of the torsional behavior of UHPC structures. In this study, the proposed torsional design adopts a modified thin-walled tube theory so as to consider the tensile behavior of UHPC. And torsion test was conducted on thin-walled UHPC box beams to validate the proposed formula through comparison of the predicted torsional strength with the experimental results. The comparison of the predicted values of the cracking torque and torsional moment resistance with those observed in the torsional test of UHPC verified the validity of the design method. The contribution of the steel fibers to the torsional strength and cracking load was larger than that of the stirrups, but the stirrups appeared to contribute additionally to the torsional ductility. Accordingly, it is recommended that design should exploit effectively the contribution of the steel fiber rather than arrange a larger number of stirrups in UHPC structures subjected to torsion.展开更多
Aiming at overcoming the difficulties in integral forming of thin-walled tubes with complex shapes, a novel forming method by inner and outer pressure through viscous was proposed. In this method, by dividing large de...Aiming at overcoming the difficulties in integral forming of thin-walled tubes with complex shapes, a novel forming method by inner and outer pressure through viscous was proposed. In this method, by dividing large deformation of the part into inner and outer pressure forming deformations, the limit deformation of tube part can be increased by several times. Meanwhile, the principle of viscous inner and outer pressure forming was provided, and key problems during the forming process such as reduction of the wall-thickness and instability wrinkling were analyzed. Thereby, the complex curved surface super-alloy GH3044 thin-walled tube with varying diameter ratio of 1.35(the ratio between the maximum and minimum diameters of the part) can be integrally formed by this method. The experimental surface of the formed part is superior in quality and the wall-thickness distribution is uniform. The results show that the viscous inner and outer pressure forming can provide a new approach for integral forming of thin-walled tubes with complex shapes.展开更多
Both experimental and mechanical analyses were carried out to investigate the characteristics of thickness distribution for tailor-welded tube (TWT) hydroforming with dissimilar thickness. Then, the effects of weld-se...Both experimental and mechanical analyses were carried out to investigate the characteristics of thickness distribution for tailor-welded tube (TWT) hydroforming with dissimilar thickness. Then, the effects of weld-seam position and thickness difference were also revealed. A multiple-diameter tube was formed to reveal the characteristics and the regularity of thickness distribution during TWT hydroforming. It is indicated that there are obvious fluctuations in thickness distribution though the TWTs have the same expansion ratio. The thinning ratio of thinner tube is bigger than that of thicker tube especially in the zone closed to the weld-seam. The difference in thinning ratio between two tube segments can reach 9%. Consequently, sudden and large fluctuation of thickness appears in the zone nearby the weld-seam. The difference in thinning ratio between thinner and thicker tubes enlarges as the thickness difference increases, but improves as length ratio increases. Different strain states are the main reason to induce nonuniform thickness distribution. The difference in thickness is the main reason to induce different strain states on thinner and thicker tubes.展开更多
The out-of-plane distortion induced in a multi-pass circumferential fillet welding of tube to pipe under different weld sequences and directions was studied using Finite Element Method(FEM) based Sysweld software and ...The out-of-plane distortion induced in a multi-pass circumferential fillet welding of tube to pipe under different weld sequences and directions was studied using Finite Element Method(FEM) based Sysweld software and verified experimentally. The FEM analyses consisted of thermal and mechanical analyses.Thermal analysis was validated with experimental transient temperature measurements. In the mechanical analysis, three different weld sequences and directions were considered to understand the mechanism of out-of-plane distortion in the tube to pipe T-joints. It was learnt that the welding direction plays a major role in minimizing the out-of-plane distortion. Further, during circumferential fillet welding of the tube to pipe component, the out-of-plane distortion generated in the x direction was primarily influenced by heat input due to the start and stop points, whereas the distortion in the z direction was influenced by time lag and welding direction. The FEM predicted distortion was compared with experimental measurements and the mechanism of out-of-plane distortion was confirmed.展开更多
To reveal the reason of weld-line movement in hydroforming of a tailor-welded tube (TWT) with dissimilar thickness,the stress ratio of axial stress to circumferential stress is derived by mechanical analysis and analy...To reveal the reason of weld-line movement in hydroforming of a tailor-welded tube (TWT) with dissimilar thickness,the stress ratio of axial stress to circumferential stress is derived by mechanical analysis and analyzed between the thicker and thinner tubes,as well as the property of the axial strain. During TWT hydroforming,tensile strain along axial direction happens on the thinner tube. On the contrary,compressive strain happens on the thicker tube. Experiments are conducted to varify the weld-line movement regularity and strain distribution. It indicates that the weld-line moves from the thinner part to the thicker during TWT hydroforming. The thinning ratio of the thinner tube is bigger than that of the thicker tube,especially in the zone near weldline. Stress ratio difference between the thicker tube and the thinner tube is the main reason of weld-line movement and non-uniform thinning ratio distribution.展开更多
Based on the assumption that profile of thin walled tube in free hydro-bulging process is a quadratic curve and any point on the profile moves vertically to the profile, mathematical models were deduced for analyzing ...Based on the assumption that profile of thin walled tube in free hydro-bulging process is a quadratic curve and any point on the profile moves vertically to the profile, mathematical models were deduced for analyzing the deformation behavior. The critical pressure and the maximum bulge coefficient(height) at bursting can be determined based on the models, in which a shape factor a is introduced to tightly communicate the material property and geometric parameters to plastic deformation. Free hydro-bulging experiments of stainless steel and low carbon steel tubes were conducted to validate the models, and the experimental data indicate that the theoretical predictions are reliable and accurate. The results display that the profile, dependent on the material and geometric parameters, can be hyperbola, parabola, arc and ellipse or alternative among them; moreover, the forming pressure and forming limit are both closely connected with material and geometric parameters.展开更多
The mechanical characteristics of the weld joint were investigated by tensile test, microstructure test, and microhardness test. The welded tube NC bending tests were carried out to evaluate the weld on the formabilit...The mechanical characteristics of the weld joint were investigated by tensile test, microstructure test, and microhardness test. The welded tube NC bending tests were carried out to evaluate the weld on the formability of the QSTE340 welded tube. The results show that the wall thinning degree, cross-sectional deformation and springback angle increase significantly as the weld line is located on the outside of the bend compared with that located on the middle and inside, and the welded tubes produce nearly identical performance as the weld line is located on the middle and inside. The wall thickening degree decreases much as the weld line is located on the inside of the bend. So the welded tube can acquire good bending formability as the weld line is located in the region away from the outside of the bend.展开更多
A new horizontal continuous casting method with heating-cooling combined mold (HCCM) technology was explored for fabri- cating high-quality thin-wall cupronickel alloy tubes used for heat exchange pipes. The microst...A new horizontal continuous casting method with heating-cooling combined mold (HCCM) technology was explored for fabri- cating high-quality thin-wall cupronickel alloy tubes used for heat exchange pipes. The microstructure and mechanical properties of BFe 10 cupronickel alloy tubes fabricated by HCCM and traditional continuous casting (cooling mold casting) were comparatively investigated. The results show that the tube fabricated by HCCM has smooth internal and external surfaces without any defects, and its internal and external surface roughnesses are 0.64 μm and 0.85 μm, respectively. The tube could be used for subsequent cold processing without other treatments such as surface planning, milling and acid-washing. This indicates that HCCM can effectively reduce the process flow and improve the pro- duction efficiency of a BFel0 cupronickel alloy tube. The tube has columnar grains along its axial direction with a major casting texture of {012}〈 621 〉. Compared with cooling mold casting (6 = 36.5%), HCCM can improve elongation (3 = 46.3%) by 10% with a slight loss of strength, which indicates that HCCM remarkably improves the cold extension performance of a BFe 10 cupronickel alloy tube.展开更多
The formed characteristics of thin-wall part is studied when it is in the process of MPAW. Finite element method is used to sinmlate the temperature field coupling flow field in the welding of thin-wall part. It is fo...The formed characteristics of thin-wall part is studied when it is in the process of MPAW. Finite element method is used to sinmlate the temperature field coupling flow field in the welding of thin-wall part. It is found that because of the obvious effect of heat accumution in cross-section, where the distribution of temperature field area presents trapezoidal inverted approximately in the molten pool and the non-molten pool area presents level. The surface tension, the electromagnetic force and buoyancy are considered for analyzing the effects on the fluid flow of welding-pool. It can be obtained that the surface tension is the main driving force in the welding pool, which is far greater than electromagnetic force and buoyancy.展开更多
In cold roll forming, steel pipes are welded with different technology parameters in order to improve the steel pipe's quality, thus we should optimize the technology parameters for producing steel pipes. By means of...In cold roll forming, steel pipes are welded with different technology parameters in order to improve the steel pipe's quality, thus we should optimize the technology parameters for producing steel pipes. By means of metallographic examination, scanning electron microscope examination, hardness test, impact test, bend test, tensile test and so on, the microstructure and mechanical properties of the steel pipes were investigated. The test results show that welding defects such as crack and blowholes are not found. The microstructure of the welded metal is Widmanstatten ; the microstructure of the heat affected zone is Widmanstatten, pearlite and proeutectoid ferrite, and the base metal is pearlite and ferrite. The highest of the metal Brinell hardness is in the weld seam, followed by the heat affected zone, and the lowest is in the base metal. The microstructure of the weld metal is coarse, which results in that the toughness of the weld is the lowest, but the hardness of the welds is the highest in the weld zone. The bend angles of the weld metal present a mountainous shape with the surface energy. Only when the surface energy is of the best value, the mechanical properties of the weld metal is the best.展开更多
This investigation focused on the influence of the radial inertia effect on the propagation behavior of stress waves in thin-walled tubes subjected to combined longitudinal and torsional impact loads.Generalized chara...This investigation focused on the influence of the radial inertia effect on the propagation behavior of stress waves in thin-walled tubes subjected to combined longitudinal and torsional impact loads.Generalized characteristics theory was used to analyze the main features of the characteristic wave speeds and simple wave solutions in thin-walled tubes.The incremental elastic-plastic constitutive relations described by the rate-independent plasticity were adopted,and the finite difference method was used to investigate the evolution and propagation behaviors of combined elasticplastic stress waves in thin-walled tubes when the radial inertial effect was considered.The numerical results were compared with those obtained when the radial inertia effect was not considered.The results showed that the speed of the coupled stress wave increased when the radial inertia effect was considered.The hardening modulus of the material in the plastic stage had a greater impact on the coupled slow waves than on the coupled fast waves.展开更多
基金Project supported by the National Natural Science Foundation of China(No.11072240)
文摘The incremental constitutive relation and governing equations with combined stresses for phase transition wave propagation in a thin-walled tube are established based on the phase transition criterion considering both the hydrostatic pressure and the deviatoric stress. It is found that the centers of the initial and subsequent phase transition ellipses are shifted along the sigma-axis in the sigma tau-plane due to the tension-compression asymmetry induced by the hydrostatic pressure. The wave solution offers the 'fast' and 'slow' phase transition waves under combined longitudinal and torsional stresses in the phase transition region. The results show some new stress paths and wave structures in a thin-walled tube with phase transition, differing from those of conventional elastic-plastic materials.
文摘An in-depth analysis of propagation characteristics ofelasto-plastic combined stress waves in circular thin-walled tubeshas been made. In obtaining the simple-wave solution, however, mostresearches have ignored the influence of the circumferential stressrelated to the radial inertial ef- fect in the tubes. In this paperthe incremental elasto-plastic constitutive relations which areconve- nient for dynamic numerical analysis are adopted, and thefinite-difference method is used to study the evolution adpropagation of elasto-plastic combined stress waves in a thin-walledtube with the radial inertial effect of the tube considered. Thecalculation results are compared with those obtained when the radialinertial effect is not considered. The calculation results show thatthe radial inertial effect of a tube has a fairly great influence onthe propagation of elasto-plastic combined stress waves.
文摘An experimental investigation was carried out to study the energy absorption characteristics of thin-walled square tubes subjected to dynamic crushing by impact loading to develop the optimum structural members. Here, the controller is introduced to improve and control the absorbed energy of thin-walled square tubes in this paper. When the controller were used, the experimental results of crushing of square tubes controlled by the controller's elements showed a good candidate for a controllable energy absorption capability in impact crushing.
基金supported by "Eleven Five Years Plan" Basic Research Item of National Defense of China (Grant No. B2220060048)
文摘Cross-section deformation is one of important factors affecting the quality of tube formation, and the tube's capability of transporting liquid and gas will be reduced because of the cross-section ellipse deformation due to the effect of shear load in plastic bending process. When the tube is bent, the extrados-wall bears the tension stress and the intrados-wall bears the compression stress, synchronously the cross-section is affected by the circumferential stress. According to the above, the distribution function and curve of tangential stress can be obtained according to force balance differential equations on circumferential direction and Trasca rule. Subsequently the real state and virtual state moment equations were established, a new method was presented adopting the virtual principle of deformation system to calculate the x-axis and y-axis displacement of arbitrary point on cross-section. So the major and minor axes of deformed cross-section can be calculated according to the displacements of each point, and the variety value of major and minor axes will be obtained further. Finally the theoretical calculating result is compared with NC tube rotary-bending experiment results to verify the rationality of theoretical analysis, and the cross-section deformation rule of thin-walled tube can be received.
基金supported by National Natural Science Foundation ofChina(Grant No.50935002)
文摘The thin-walled tube flexure(TWTF) hinges have important potential application value in the deployment mechanisms of satellite and solar array, but the optimal design of the TWTF hinges haven't been completely solved, which restricts their applications. An optimal design method for the qusai-static folding and deploying of TWTF hinges with double slots is presented based on the response surface theory. Firstly, the full factorial method is employed to design of the experiments. Then, the finite element models of the TWTF hinges with double slots are constructed to simulate the qusai-static folding and deploying non-linear analysis. What's more, the mathematical model of the TWTF flexure hinge quasi-static folding and deploying properties are derived by the response surface method. Considering of small mass and high stability, the peak moment of quasi-static folding and deploying as well as the lightless are set as the objectives to get the optimal performances. The relative errors of the objectives between the optimal design results and the FE analysis results are less than 7%, which demonstrates the precision of the surrogate models. Lastly, the parameter study shows that both the slots length and the slots width both have significant effects to the peak moment of quasi-static folding and deploying of TWTF hinges with double slots. However, the maximum Mises stress of quasi-static folding is more sensitive to the slots length than the slots width. The proposed research can be applied to optimize other thin-walled flexure hinges under quasi-static folding and deploying, which is of great importance to design of flexure hinges with high stability and low stress.
文摘High frequency shock load is often generated during pyrotechnic device working, which is detrimental to spacecraft structures and electric devices. Therefore, it is valuable to reduce the shock load in pyrotechnic device design. Actually, there are several ways to decrease pyroshock loads, such as reduction of powder,installation of buffering structure, insulation of damageable devices, and so on. Considered assuring the function of pyrotechnic device and minimum of structure modification, shock absorbing structure is more propitious to be introduced in pyrotechnic device. In this paper, based on the method of thinwalled metal tube diameter-expanding, a thin-walled tube shock buffering structure was designed on a separate bolt. Built on the simplified structure of a separate bolt, the model of cone piston impacting thin-walled tube absorber was established, and the thin-walled tube shock absorbing characteristics and the relation between cone angles and absorber performance were analyzed. The results showed that the change of buffering force of thin-walled tube could be divided into four phases, and each phase was correspondent to the cone piston structure. In addition, as the cone angle increases, the max shock acceleration changes in the style of decrease-increase-decrease-increase, which is the result of coupled effects of cone piston max enter depth, buffering force and energy loss. In short, these results could establish the relationships between thin-walled tube absorbing performance and its structure, which is of significance to develop low-shock pyrotechnic device.
基金This work was supported by the National Natural Science Foundation of China for Distinguished Young Scholars (Grant No. 50225518)the Teaching and Research Award Program for 0utstanding Young Teachers in Higher Education Institution of M0E, PRCthe Aeronautical Science Foundation of China (Grant No. 04H53057).
文摘Springback is one of important factors influencing the forming quality of numerical control (NC) bending of thin-walled tube. In this paper, a numerical-analytic method for springback angle prediction of the process was put forward. The method is based on springback angle model derived using analytic method and simulation results from three-dimensional (3D) rigid-plastic finite element method (FEM). The method is validated through comparison with experimental results. The features of the method are as follows: (1) The method is high in efficiency because it combines advantages of rigid-plastic FEM and analytic method. (2) The method is satisfactory in accuracy, since the field variables used in the model is resulting from 3D rigid-plastic FEM solution, and the effects both of axial force and strain neutral axis shift have been included. (3) Research on multi-factor effects can be carried out using the method due to its advantage inheriting from rigid-plastic FEM. The method described here is also of general significance to other bending processes.
文摘This study proposed a prediction formula for the torsional strength enabling to reflect the tensile strength of ultra high performance concrete (UHPC) beams based upon the thin-walled tube theory. The remarkable ductile behavior of UHPC can also be attributed to the steel fiber reinforcement. This feature must be considered to provide rational explanation of the torsional behavior of UHPC structures. In this study, the proposed torsional design adopts a modified thin-walled tube theory so as to consider the tensile behavior of UHPC. And torsion test was conducted on thin-walled UHPC box beams to validate the proposed formula through comparison of the predicted torsional strength with the experimental results. The comparison of the predicted values of the cracking torque and torsional moment resistance with those observed in the torsional test of UHPC verified the validity of the design method. The contribution of the steel fibers to the torsional strength and cracking load was larger than that of the stirrups, but the stirrups appeared to contribute additionally to the torsional ductility. Accordingly, it is recommended that design should exploit effectively the contribution of the steel fiber rather than arrange a larger number of stirrups in UHPC structures subjected to torsion.
基金Funded by the National Natural Science Foundation of China(No.51205260)
文摘Aiming at overcoming the difficulties in integral forming of thin-walled tubes with complex shapes, a novel forming method by inner and outer pressure through viscous was proposed. In this method, by dividing large deformation of the part into inner and outer pressure forming deformations, the limit deformation of tube part can be increased by several times. Meanwhile, the principle of viscous inner and outer pressure forming was provided, and key problems during the forming process such as reduction of the wall-thickness and instability wrinkling were analyzed. Thereby, the complex curved surface super-alloy GH3044 thin-walled tube with varying diameter ratio of 1.35(the ratio between the maximum and minimum diameters of the part) can be integrally formed by this method. The experimental surface of the formed part is superior in quality and the wall-thickness distribution is uniform. The results show that the viscous inner and outer pressure forming can provide a new approach for integral forming of thin-walled tubes with complex shapes.
基金Projects(51005054, 50575051) supported by the National Natural Science Foundation of ChinaProject(HIT.BRETI.2010010) supported by the Fundamental Research Funds for the Central Universities, ChinaProject(20100471025) supported by the National Science Foundation for Post-doctoral Scientists of China
文摘Both experimental and mechanical analyses were carried out to investigate the characteristics of thickness distribution for tailor-welded tube (TWT) hydroforming with dissimilar thickness. Then, the effects of weld-seam position and thickness difference were also revealed. A multiple-diameter tube was formed to reveal the characteristics and the regularity of thickness distribution during TWT hydroforming. It is indicated that there are obvious fluctuations in thickness distribution though the TWTs have the same expansion ratio. The thinning ratio of thinner tube is bigger than that of thicker tube especially in the zone closed to the weld-seam. The difference in thinning ratio between two tube segments can reach 9%. Consequently, sudden and large fluctuation of thickness appears in the zone nearby the weld-seam. The difference in thinning ratio between thinner and thicker tubes enlarges as the thickness difference increases, but improves as length ratio increases. Different strain states are the main reason to induce nonuniform thickness distribution. The difference in thickness is the main reason to induce different strain states on thinner and thicker tubes.
文摘The out-of-plane distortion induced in a multi-pass circumferential fillet welding of tube to pipe under different weld sequences and directions was studied using Finite Element Method(FEM) based Sysweld software and verified experimentally. The FEM analyses consisted of thermal and mechanical analyses.Thermal analysis was validated with experimental transient temperature measurements. In the mechanical analysis, three different weld sequences and directions were considered to understand the mechanism of out-of-plane distortion in the tube to pipe T-joints. It was learnt that the welding direction plays a major role in minimizing the out-of-plane distortion. Further, during circumferential fillet welding of the tube to pipe component, the out-of-plane distortion generated in the x direction was primarily influenced by heat input due to the start and stop points, whereas the distortion in the z direction was influenced by time lag and welding direction. The FEM predicted distortion was compared with experimental measurements and the mechanism of out-of-plane distortion was confirmed.
基金Sponsored by the National Natural Science Foundation of China(Grant No 50575051)Program for New Century Excellent Talents in University(Grant No NCET-07-0237)
文摘To reveal the reason of weld-line movement in hydroforming of a tailor-welded tube (TWT) with dissimilar thickness,the stress ratio of axial stress to circumferential stress is derived by mechanical analysis and analyzed between the thicker and thinner tubes,as well as the property of the axial strain. During TWT hydroforming,tensile strain along axial direction happens on the thinner tube. On the contrary,compressive strain happens on the thicker tube. Experiments are conducted to varify the weld-line movement regularity and strain distribution. It indicates that the weld-line moves from the thinner part to the thicker during TWT hydroforming. The thinning ratio of the thinner tube is bigger than that of the thicker tube,especially in the zone near weldline. Stress ratio difference between the thicker tube and the thinner tube is the main reason of weld-line movement and non-uniform thinning ratio distribution.
文摘Based on the assumption that profile of thin walled tube in free hydro-bulging process is a quadratic curve and any point on the profile moves vertically to the profile, mathematical models were deduced for analyzing the deformation behavior. The critical pressure and the maximum bulge coefficient(height) at bursting can be determined based on the models, in which a shape factor a is introduced to tightly communicate the material property and geometric parameters to plastic deformation. Free hydro-bulging experiments of stainless steel and low carbon steel tubes were conducted to validate the models, and the experimental data indicate that the theoretical predictions are reliable and accurate. The results display that the profile, dependent on the material and geometric parameters, can be hyperbola, parabola, arc and ellipse or alternative among them; moreover, the forming pressure and forming limit are both closely connected with material and geometric parameters.
基金Supported by National Natural Science Foundation of China (No. 50875216)
文摘The mechanical characteristics of the weld joint were investigated by tensile test, microstructure test, and microhardness test. The welded tube NC bending tests were carried out to evaluate the weld on the formability of the QSTE340 welded tube. The results show that the wall thinning degree, cross-sectional deformation and springback angle increase significantly as the weld line is located on the outside of the bend compared with that located on the middle and inside, and the welded tubes produce nearly identical performance as the weld line is located on the middle and inside. The wall thickening degree decreases much as the weld line is located on the inside of the bend. So the welded tube can acquire good bending formability as the weld line is located in the region away from the outside of the bend.
基金supported by the National High Technology Research and Development Program of China (No.2011BAE23B00)
文摘A new horizontal continuous casting method with heating-cooling combined mold (HCCM) technology was explored for fabri- cating high-quality thin-wall cupronickel alloy tubes used for heat exchange pipes. The microstructure and mechanical properties of BFe 10 cupronickel alloy tubes fabricated by HCCM and traditional continuous casting (cooling mold casting) were comparatively investigated. The results show that the tube fabricated by HCCM has smooth internal and external surfaces without any defects, and its internal and external surface roughnesses are 0.64 μm and 0.85 μm, respectively. The tube could be used for subsequent cold processing without other treatments such as surface planning, milling and acid-washing. This indicates that HCCM can effectively reduce the process flow and improve the pro- duction efficiency of a BFel0 cupronickel alloy tube. The tube has columnar grains along its axial direction with a major casting texture of {012}〈 621 〉. Compared with cooling mold casting (6 = 36.5%), HCCM can improve elongation (3 = 46.3%) by 10% with a slight loss of strength, which indicates that HCCM remarkably improves the cold extension performance of a BFe 10 cupronickel alloy tube.
基金supported by the National Natural Science Foundation of China(Grant No.U1333128,U1733125)Science and Technology Project of Tianjin(Grant No.14ZCDZGX00802,17JCZDJC38700)
文摘The formed characteristics of thin-wall part is studied when it is in the process of MPAW. Finite element method is used to sinmlate the temperature field coupling flow field in the welding of thin-wall part. It is found that because of the obvious effect of heat accumution in cross-section, where the distribution of temperature field area presents trapezoidal inverted approximately in the molten pool and the non-molten pool area presents level. The surface tension, the electromagnetic force and buoyancy are considered for analyzing the effects on the fluid flow of welding-pool. It can be obtained that the surface tension is the main driving force in the welding pool, which is far greater than electromagnetic force and buoyancy.
文摘In cold roll forming, steel pipes are welded with different technology parameters in order to improve the steel pipe's quality, thus we should optimize the technology parameters for producing steel pipes. By means of metallographic examination, scanning electron microscope examination, hardness test, impact test, bend test, tensile test and so on, the microstructure and mechanical properties of the steel pipes were investigated. The test results show that welding defects such as crack and blowholes are not found. The microstructure of the welded metal is Widmanstatten ; the microstructure of the heat affected zone is Widmanstatten, pearlite and proeutectoid ferrite, and the base metal is pearlite and ferrite. The highest of the metal Brinell hardness is in the weld seam, followed by the heat affected zone, and the lowest is in the base metal. The microstructure of the weld metal is coarse, which results in that the toughness of the weld is the lowest, but the hardness of the welds is the highest in the weld zone. The bend angles of the weld metal present a mountainous shape with the surface energy. Only when the surface energy is of the best value, the mechanical properties of the weld metal is the best.
文摘This investigation focused on the influence of the radial inertia effect on the propagation behavior of stress waves in thin-walled tubes subjected to combined longitudinal and torsional impact loads.Generalized characteristics theory was used to analyze the main features of the characteristic wave speeds and simple wave solutions in thin-walled tubes.The incremental elastic-plastic constitutive relations described by the rate-independent plasticity were adopted,and the finite difference method was used to investigate the evolution and propagation behaviors of combined elasticplastic stress waves in thin-walled tubes when the radial inertial effect was considered.The numerical results were compared with those obtained when the radial inertia effect was not considered.The results showed that the speed of the coupled stress wave increased when the radial inertia effect was considered.The hardening modulus of the material in the plastic stage had a greater impact on the coupled slow waves than on the coupled fast waves.