The internal residual stress within a TC 17 titanium alloy joint welded by linear friction welding (LFW) was measured by the contour method, which is a relatively new and destructive technique to obtain a full map o...The internal residual stress within a TC 17 titanium alloy joint welded by linear friction welding (LFW) was measured by the contour method, which is a relatively new and destructive technique to obtain a full map of internal residual stress. The specimen was first cut into two parts; the out-of-plane displacement contour formed by the release of the residual stress was then measured; finally, taking the measured contour of the cut plane as the boundary conditions, a linear elastic finite element analysis was carried out to calculate the corresponding distribution of residual stress normal to the cut plane. The internal stress distribution of the TC 17 titanium alloy LFWjoint was also analyzed. The results show that the tensile residual stress in the TC17 LFW weld is mainly present within a region about 12 mm from the weld centerline; the peak tensile residual stress occurs at the weld centerline and reaches 360 MPa (about one third of the yield strength of TC17 alloy); within the weld zone of the TC17 LFW weld, the through-thickness stress is not uniform, and the internal stress is larger than that near the top or bottom surface.展开更多
Friction stir welding between AA5052-H32aluminium plates is performed by central composite design technique of response surface methodology.It is found that the welding parameters such as tool pin profile,tool rotatio...Friction stir welding between AA5052-H32aluminium plates is performed by central composite design technique of response surface methodology.It is found that the welding parameters such as tool pin profile,tool rotational speed,welding speed,and tool tilt angle play a major role in deciding the joint characteristics.The joints fabricated using tapered square pin profile tool with a tool rotational speed of600r/min,welding speed of65mm/min,and tool tilt angle of1.5°result in an unexpected weld efficiency of93.51%.Mathematical models are developed to map the correlation between the parameters and responses(ultimate tensile strength and elongation)and these models are optimized to maximize the ultimate tensile strength of the friction stir welded joint.Response plots generated from the mathematical models are used to interpret the interaction effects of the welding parameters on the response variables.Adequacy of the developed models is validated using analysis of variance(ANOVA)technique.Results from the confirmatory experiments plotted in scatter diagram show a good agreement with predicted models.Different grain structures in various zones of the weld are examined by observing the micro and macro structures of the weld.展开更多
In this paper a new method for preventing welding hot cracking—the inverse strain method(ISM)is developed on the principle of welding mechan- ics.Effectiveness and feasiblity of method in preventing welding hot crack...In this paper a new method for preventing welding hot cracking—the inverse strain method(ISM)is developed on the principle of welding mechan- ics.Effectiveness and feasiblity of method in preventing welding hot cracking of high strength aluminum alloy LY12CZ by synchronous rolling during welding (SRDW)along both sides of the weld at a suitable distance behind the welding arc are examined.Experimental resulte indicate that welding hot cracking of LY12CY can be effectively prevented and the mechanical properties of welded joint can also be improved by the method.It is an important new solution for preventing hot cracking in welding of sheet metal.展开更多
In order to explore the influence of welding parameters and to investigate the Al alloy (AA) nugget formation process, a comprehensive model involving electrical-thermal-mechanical and metallurgical analysis was estab...In order to explore the influence of welding parameters and to investigate the Al alloy (AA) nugget formation process, a comprehensive model involving electrical-thermal-mechanical and metallurgical analysis was established to numerically display the resistance spot welding (RSW) process within multiple fields and understand the AA-RSW physics. A multi-disciplinary finite element method (FEM) framework and a empirical sub-model were built to analyze the affecting factors on weld nugget and the underlying nature of welding physics with dynamic simulation procedure. Specifically, a counter-intuitive phenomenon of the resistance time-variation caused by the transient inverse virtual variation (TIVV) effect was highlighted and analyzed on the basis of welding current and temperature distribution simulation. The empirical model describing the TIVV phenomenon was used for modifying the dynamic resistance simulation during the AA spot welding process. The numerical and experimental results show that the proposed multi-field FEM model agrees with the measured AA welding feature, and the modified dynamic resistance model captures the physics of nugget growth and the electrical-thermal behavior under varying welding current and fluctuating heat input.展开更多
A two-dimensional computational fluid dynamics model was established to simulate the friction stir butt-welding of 6061 aluminum alloy. The dynamic mesh method was applied in this model to make the tool move forward a...A two-dimensional computational fluid dynamics model was established to simulate the friction stir butt-welding of 6061 aluminum alloy. The dynamic mesh method was applied in this model to make the tool move forward and rotate in a manner similar to a real tool, and the calculated volumetric source of energy was loaded to establish a similar thermal environment to that used in the experiment. Besides, a small piece of zinc stock was embedded into the workpiece as a trace element. Temperature fields and vector plots were determined using a finite volume method, which was indirectly verified by traditional metallography. The simulation result indicated that the temperature distribution was asymmetric but had a similar tendency on the two sides of the welding line. The maximum temperature on the advancing side was approximately 10 K higher than that on the retreating side. Furthermore, the precise process of material flow behavior in combination with streamtraces was demonstrated by contour maps of the phases. Under the shearing force and forward extrusion pressure, material located in front of the tool tended to move along the tangent direction of the rotating tool. Notably, three whirlpools formed under a special pressure environment around the tool, resulting in a uniform composition distribution.展开更多
A comparative approach was performed between the response surface method(RSM) and the adaptive neuro-fuzzy inference system(ANFIS) to enhance the tensile properties, including the ultimate tensile strength and the ten...A comparative approach was performed between the response surface method(RSM) and the adaptive neuro-fuzzy inference system(ANFIS) to enhance the tensile properties, including the ultimate tensile strength and the tensile elongation, of friction stir welded age hardenable AA6061 and AA2024 aluminum alloys. The effects of the welding parameters, namely the tool rotational speed, welding speed, axial load and pin profile, on the ultimate tensile strength and the tensile elongation were analyzed using a three-level, four-factor Box-Behnken experimental design. The developed design was utilized to train the ANFIS models. The predictive capabilities of RSM and ANFIS were compared based on the root mean square error, the mean absolute error, and the correlation coefficient based on the obtained data set. The results demonstrate that the developed ANFIS models are more effective than the RSM model.展开更多
Identification of process parameters,their effects and contributions to the outcomes of the system using experimental approach could be a daunting,time consuming,and costly course.Using proper statistical methods,i.e....Identification of process parameters,their effects and contributions to the outcomes of the system using experimental approach could be a daunting,time consuming,and costly course.Using proper statistical methods,i.e.,Taguchi method,could significantly reduce the number of required experiments and statistical significance of the parameter can be identified.Friction stir welding is one of those welding techniques with many parameters which have different effects on the quality of the welds.In friction stir welding the tool rotational speed(RPM)and transverse speed(mm/min)influence the strength(i.e.,hardness distribution)of the stirred zone.In this study,these two factors are investigated to determine the effect they will have on the hardness in the stirred zone of the friction stir welds and how the two factors are related to one another for as-cast magnesium alloy AM60 with nominal chemical composition of Mg-(5.5-6.5)Al-(0.24-0.6)Mn-0.22Zn-0.1Si.Experimental data was taken at three different tool rotational speeds and three different transverse speeds.The data obtained was then analyzed using a 32 factorial design to find the contribution of these parameters.It was determined that both tool rotational speed and transverse speed possess significant effects on the stir zone hardness.Also,the interactions between the two factors were statistically assessed.展开更多
Though the preferred welding process to weld aluminium alloy is frequently constant current gas tungsten arc welding (CCGTAW),it resulted in grain coarsening at the fusion zone and heat affected zone(HAZ).Hence,pulsed...Though the preferred welding process to weld aluminium alloy is frequently constant current gas tungsten arc welding (CCGTAW),it resulted in grain coarsening at the fusion zone and heat affected zone(HAZ).Hence,pulsed current gas tungsten arc welding(PCGTAW) was performed,to yield finer fusion zone grains,which leads to higher strength of AA6061 (Al-Mg-Si) aluminium alloy joints.In order to determine the most influential control factors which will yield minimum fusion zone grain size and maximum tensile strength of the joints,the traditional Hooke and Jeeves pattern search method was used.The experiments were carried out based on central composite design with 31 runs and an algorithm was developed to optimize the fusion zone grain size and the tensile strength of pulsed current gas tungsten arc welded AA6061 aluminium alloy joints.The results indicate that the peak current (Ip) and base current (IB) are the most significant parameters,to decide the fusion zone grain size and the tensile strength of the AA6061 aluminum alloy joints.展开更多
Effects of welding current on temperature and velocity fields during gas metal arc welding(GMAW) of commercially pure aluminum were simulated. Equations of conservation of mass, energy and momentum were solved in a th...Effects of welding current on temperature and velocity fields during gas metal arc welding(GMAW) of commercially pure aluminum were simulated. Equations of conservation of mass, energy and momentum were solved in a three-dimensional transient model using FLOW-3 D software. The mathematical model considered buoyancy and surface tension driving forces. Further, effects of droplet heat content and impact force on weld pool surface deformation were added to the model. The results of simulation showed that an increase in the welding current could increase peak temperature and the maximum velocity in the weld pool. The weld pool dimensions and width of the heat-affected zone(HAZ) were enlarged by increasing the welding current. In addition, dimensionless Peclet, Grashof and surface tension Reynolds numbers were calculated to understand the importance of heat transfer by convection and the roles of various driving forces in the weld pool. In order to validate the model, welding experiments were conducted under several welding currents. The predicted weld pool dimensions were compared with the corresponding experimental results, and good agreement between simulation and preliminary test results was achieved.展开更多
By measuring and analyzing infrared thermal image of the specimen in static load tensile test process, it was studied that the influence of the undercut defects and double-sided dressing method on the deformation beha...By measuring and analyzing infrared thermal image of the specimen in static load tensile test process, it was studied that the influence of the undercut defects and double-sided dressing method on the deformation behavior of the laser welded joint specimens of TC4 titanium alloy. The results showed that for the unmodified specimens, the yield phenomenon occurs first in the region of the joint, but the undercut value has an effect on the stress and strain of starting to yield phenomenon, and a great effect on the plastic deformation behavior.When the undercut is less than a certain value, the large plastic deformation occurs in the base metal region and the plasticity of the specimen is comparable to that of the base metal, but the larger undercut defect results in a concentrated plastic deformation in the joint region and rapidly failed in this region. But the double-sided dressing specimen is significantly different. The physical yield is no longer concentrated in the joint region, but at the same time occurs in the several regions including joint and the base metal. And the plastic deformation mainly occurs in the base material area, similar to that of the base material.展开更多
To solve the difficulty in the explosive welding of corrosion-resistant aluminum and stainless steel tubes, three technologies were proposed after investigating the forming mechanism through experiments. Then, a 3D fi...To solve the difficulty in the explosive welding of corrosion-resistant aluminum and stainless steel tubes, three technologies were proposed after investigating the forming mechanism through experiments. Then, a 3D finite element model was established for systematic simulations in the parameter determination. The results show that the transition-layer approach, the coaxial initial assembly of tubes with the top-center-point the detonation, and the systematic study by numerical modeling are the key technologies to make the explosive welding of LF6 aluminum alloy and 1Cr18Ni9Ti stainless steel tubes feasible. Numerical simulation shows that radial contraction and slope collision through continuous local plastic deformation are necessary for the good bonding of tubes. Stand-off distances between tubes (D1 and D2) and explosives amount (R) have effect on the plastic deformation, moving velocity, and bonding of tubes. D1 of 1 mm, D2 of 2 mm, and R of 2/3 are suitable for the explosive welding of LF6-L2-1Cr18Ni9Ti three-layer tubes. The plastic strain and moving velocity of the flyer tubes in-crease with the increase of stand-off distance. More explosives (R2/3) result in the asymmetrical distribution of plastic strain and non-bonding at the end of detonation on the tubes.展开更多
The characteristics of temperatures, stresses and strains fields have been studied numerically for a titanium alloy sheet welded with an improved gas tungsten arc welding method, in which a trailing spot heat sink is ...The characteristics of temperatures, stresses and strains fields have been studied numerically for a titanium alloy sheet welded with an improved gas tungsten arc welding method, in which a trailing spot heat sink is introduced to control the welding stress and distortion. The impinging jet model is employed to describe the internee heat transfer between the cooling media and the top suufuce of the workpiece. The influcnee of the distance between arc and heat sink is investigated. Results show that there is an ideal range of distance. Using the ideal distance, a low stress and no distortion welding structure can be derived.展开更多
Based on the situation of welding thermal conduction and thermo-elasto-platicity research, this paper explores some problems in this field. First, the boundary element method for nonlinear problems is improved by line...Based on the situation of welding thermal conduction and thermo-elasto-platicity research, this paper explores some problems in this field. First, the boundary element method for nonlinear problems is improved by linearization of nonlinear problems and used in welding thermal conduction analysis. Second, the thermo-elasto-plastic finite element method is used for the welding stress calculation, in which the phase transformation is considered by the 'equivalent linear expansion coefficient method'. The comparison of the calculated results with experimental data shows that the methods provided in this paper are available.展开更多
A model of double grains under plane stress state has been established. According to the double grain model, thermal stress induced by thermal cycling in welding fusion zone is numerically simulated by finite element ...A model of double grains under plane stress state has been established. According to the double grain model, thermal stress induced by thermal cycling in welding fusion zone is numerically simulated by finite element method, and the microstructures before and after thermal cycling are observed. The effect of thermal stress on weld microstructure is discussed. Experimental and analysis results show that the difference between the coefficients of thermal expansion and elastic modulus for grains along different crystal directio n can produce alternate thermal misfit stress and strain near boundaries under thermal cycling. At the temperature of upper and lower limit, thermal stress nearby grain boundary reaches maxima. Thermal stress induced changes in microstructure, which expressed by the sending dislocations from boundaries to matrix, piling up against the boundaries and the increasing of dislocation density.展开更多
Alloy 690 is a typical Ni-Cr-Fe alloy, which is widely used in nuclear power application. However, filler metal 52M (FM-52M) used in alloy 690 weldment is fimnd to be susceptible to ductility-dip cracking (DDC) , ...Alloy 690 is a typical Ni-Cr-Fe alloy, which is widely used in nuclear power application. However, filler metal 52M (FM-52M) used in alloy 690 weldment is fimnd to be susceptible to ductility-dip cracking (DDC) , which seriously affects safety and life extension in nuclear application. In this paper, the DDC susceptibility of FM-52M in welding process was investigated using finite element method. At first, Gleeble-based testing technique, strain to fracture ( STF ) test, was used to evaluate the DDC susceptibility and the formation mechanism of DDC was explained. The result shows that FM-52M is most susceptible at 1 050 ℃ and grain boundary weakness at high temperature induces crack initiation. Afterwards, in order to evaluate the DDC susceptibility under complex stress state, tube-plate welding model was built by means of ABAQUS software. Susceptible regions could be confirmed associated with STF results. The simulation result shows that HAZ is the most susceptible region in FM-52M joint.展开更多
The role of oxides in the formation of hole defects in friction stir welded joint of 2519-T87 aluminum alloy has been investigated by using optical microscope, scanning electron microscope, electron backscatter diffra...The role of oxides in the formation of hole defects in friction stir welded joint of 2519-T87 aluminum alloy has been investigated by using optical microscope, scanning electron microscope, electron backscatter diffraction and electron probe microanalyzer to examine the distribution of oxides and the features of hole defects, and using ABAQUS 3D thermo-mechanical coupling finite element model based on arbitrary Lagrangian-Eulerian method to simulate the material flow behavior. Oxides exist at the edge of tunnel hole and in the micropores in the joint. Based on distribution of oxygen and material flow behavior, it is believed that the oxides on the surface of the alloy tend to flow down into the bulk along the flow direction of plastic material during friction stir welding, aggregate in the weak region of material flow at the intersection of the shoulder affected zone and the stir pin-tip affected zone, and consequently prevent the material from contacting and diffusing. Due to the insufficient material flow and therefore the small plastic deformation,the pressure is not high enough to compress the accumulated oxides, resulting in hole defects.展开更多
利用裂纹扩展分析方法和质量分类法研究铝合金车体含缺欠焊接结构的疲劳寿命问题。首先,研究IIW:2015的基于Paris定律的裂纹扩展分析的理论基础和BS 7910:2019的基于考虑焊接缺欠质量的S-N曲线的质量分类法的算法原理;其次,归纳总结了这...利用裂纹扩展分析方法和质量分类法研究铝合金车体含缺欠焊接结构的疲劳寿命问题。首先,研究IIW:2015的基于Paris定律的裂纹扩展分析的理论基础和BS 7910:2019的基于考虑焊接缺欠质量的S-N曲线的质量分类法的算法原理;其次,归纳总结了这2种方法进行考虑焊接质量的焊接结构疲劳寿命评估流程;再次,在疲劳载荷作用下,基于BS EN 1999-1-3:2007的名义应力法对某动车组铝合金车体进行疲劳分析,确定车体疲劳关切焊缝部位;最后,分别利用裂纹扩展分析方法和质量分类法对车体关切焊缝侧门下角进行考虑初始裂纹的疲劳寿命评估。结果表明:基于质量分类法的剩余寿命为1.4×106次,基于裂纹扩展分析法的剩余寿命为2.64×106次。展开更多
基金Project(35061107)supported by the Doctoral Initiation Project of Jiangsu University of Science and Technology,China
文摘The internal residual stress within a TC 17 titanium alloy joint welded by linear friction welding (LFW) was measured by the contour method, which is a relatively new and destructive technique to obtain a full map of internal residual stress. The specimen was first cut into two parts; the out-of-plane displacement contour formed by the release of the residual stress was then measured; finally, taking the measured contour of the cut plane as the boundary conditions, a linear elastic finite element analysis was carried out to calculate the corresponding distribution of residual stress normal to the cut plane. The internal stress distribution of the TC 17 titanium alloy LFWjoint was also analyzed. The results show that the tensile residual stress in the TC17 LFW weld is mainly present within a region about 12 mm from the weld centerline; the peak tensile residual stress occurs at the weld centerline and reaches 360 MPa (about one third of the yield strength of TC17 alloy); within the weld zone of the TC17 LFW weld, the through-thickness stress is not uniform, and the internal stress is larger than that near the top or bottom surface.
文摘Friction stir welding between AA5052-H32aluminium plates is performed by central composite design technique of response surface methodology.It is found that the welding parameters such as tool pin profile,tool rotational speed,welding speed,and tool tilt angle play a major role in deciding the joint characteristics.The joints fabricated using tapered square pin profile tool with a tool rotational speed of600r/min,welding speed of65mm/min,and tool tilt angle of1.5°result in an unexpected weld efficiency of93.51%.Mathematical models are developed to map the correlation between the parameters and responses(ultimate tensile strength and elongation)and these models are optimized to maximize the ultimate tensile strength of the friction stir welded joint.Response plots generated from the mathematical models are used to interpret the interaction effects of the welding parameters on the response variables.Adequacy of the developed models is validated using analysis of variance(ANOVA)technique.Results from the confirmatory experiments plotted in scatter diagram show a good agreement with predicted models.Different grain structures in various zones of the weld are examined by observing the micro and macro structures of the weld.
文摘In this paper a new method for preventing welding hot cracking—the inverse strain method(ISM)is developed on the principle of welding mechan- ics.Effectiveness and feasiblity of method in preventing welding hot cracking of high strength aluminum alloy LY12CZ by synchronous rolling during welding (SRDW)along both sides of the weld at a suitable distance behind the welding arc are examined.Experimental resulte indicate that welding hot cracking of LY12CY can be effectively prevented and the mechanical properties of welded joint can also be improved by the method.It is an important new solution for preventing hot cracking in welding of sheet metal.
基金Projects (11202125, 61175038) supported by the National Natural Science Foundation of China
文摘In order to explore the influence of welding parameters and to investigate the Al alloy (AA) nugget formation process, a comprehensive model involving electrical-thermal-mechanical and metallurgical analysis was established to numerically display the resistance spot welding (RSW) process within multiple fields and understand the AA-RSW physics. A multi-disciplinary finite element method (FEM) framework and a empirical sub-model were built to analyze the affecting factors on weld nugget and the underlying nature of welding physics with dynamic simulation procedure. Specifically, a counter-intuitive phenomenon of the resistance time-variation caused by the transient inverse virtual variation (TIVV) effect was highlighted and analyzed on the basis of welding current and temperature distribution simulation. The empirical model describing the TIVV phenomenon was used for modifying the dynamic resistance simulation during the AA spot welding process. The numerical and experimental results show that the proposed multi-field FEM model agrees with the measured AA welding feature, and the modified dynamic resistance model captures the physics of nugget growth and the electrical-thermal behavior under varying welding current and fluctuating heat input.
基金Project(51475232)supported by the National Natural Science Foundation of China
文摘A two-dimensional computational fluid dynamics model was established to simulate the friction stir butt-welding of 6061 aluminum alloy. The dynamic mesh method was applied in this model to make the tool move forward and rotate in a manner similar to a real tool, and the calculated volumetric source of energy was loaded to establish a similar thermal environment to that used in the experiment. Besides, a small piece of zinc stock was embedded into the workpiece as a trace element. Temperature fields and vector plots were determined using a finite volume method, which was indirectly verified by traditional metallography. The simulation result indicated that the temperature distribution was asymmetric but had a similar tendency on the two sides of the welding line. The maximum temperature on the advancing side was approximately 10 K higher than that on the retreating side. Furthermore, the precise process of material flow behavior in combination with streamtraces was demonstrated by contour maps of the phases. Under the shearing force and forward extrusion pressure, material located in front of the tool tended to move along the tangent direction of the rotating tool. Notably, three whirlpools formed under a special pressure environment around the tool, resulting in a uniform composition distribution.
基金Sri Chandrasekharendra Saraswathi Viswa Maha Vidyalaya, Enathur, Kanchipuram, Tamilnadu for funding this research as a university minor research project
文摘A comparative approach was performed between the response surface method(RSM) and the adaptive neuro-fuzzy inference system(ANFIS) to enhance the tensile properties, including the ultimate tensile strength and the tensile elongation, of friction stir welded age hardenable AA6061 and AA2024 aluminum alloys. The effects of the welding parameters, namely the tool rotational speed, welding speed, axial load and pin profile, on the ultimate tensile strength and the tensile elongation were analyzed using a three-level, four-factor Box-Behnken experimental design. The developed design was utilized to train the ANFIS models. The predictive capabilities of RSM and ANFIS were compared based on the root mean square error, the mean absolute error, and the correlation coefficient based on the obtained data set. The results demonstrate that the developed ANFIS models are more effective than the RSM model.
文摘Identification of process parameters,their effects and contributions to the outcomes of the system using experimental approach could be a daunting,time consuming,and costly course.Using proper statistical methods,i.e.,Taguchi method,could significantly reduce the number of required experiments and statistical significance of the parameter can be identified.Friction stir welding is one of those welding techniques with many parameters which have different effects on the quality of the welds.In friction stir welding the tool rotational speed(RPM)and transverse speed(mm/min)influence the strength(i.e.,hardness distribution)of the stirred zone.In this study,these two factors are investigated to determine the effect they will have on the hardness in the stirred zone of the friction stir welds and how the two factors are related to one another for as-cast magnesium alloy AM60 with nominal chemical composition of Mg-(5.5-6.5)Al-(0.24-0.6)Mn-0.22Zn-0.1Si.Experimental data was taken at three different tool rotational speeds and three different transverse speeds.The data obtained was then analyzed using a 32 factorial design to find the contribution of these parameters.It was determined that both tool rotational speed and transverse speed possess significant effects on the stir zone hardness.Also,the interactions between the two factors were statistically assessed.
基金Naval Research Board (NRB),Ministry of Defence,New Delhi for the financial support to carry out this investigation through sponsored project No.DNRD/05/4003/NRB/67.
文摘Though the preferred welding process to weld aluminium alloy is frequently constant current gas tungsten arc welding (CCGTAW),it resulted in grain coarsening at the fusion zone and heat affected zone(HAZ).Hence,pulsed current gas tungsten arc welding(PCGTAW) was performed,to yield finer fusion zone grains,which leads to higher strength of AA6061 (Al-Mg-Si) aluminium alloy joints.In order to determine the most influential control factors which will yield minimum fusion zone grain size and maximum tensile strength of the joints,the traditional Hooke and Jeeves pattern search method was used.The experiments were carried out based on central composite design with 31 runs and an algorithm was developed to optimize the fusion zone grain size and the tensile strength of pulsed current gas tungsten arc welded AA6061 aluminium alloy joints.The results indicate that the peak current (Ip) and base current (IB) are the most significant parameters,to decide the fusion zone grain size and the tensile strength of the AA6061 aluminum alloy joints.
文摘Effects of welding current on temperature and velocity fields during gas metal arc welding(GMAW) of commercially pure aluminum were simulated. Equations of conservation of mass, energy and momentum were solved in a three-dimensional transient model using FLOW-3 D software. The mathematical model considered buoyancy and surface tension driving forces. Further, effects of droplet heat content and impact force on weld pool surface deformation were added to the model. The results of simulation showed that an increase in the welding current could increase peak temperature and the maximum velocity in the weld pool. The weld pool dimensions and width of the heat-affected zone(HAZ) were enlarged by increasing the welding current. In addition, dimensionless Peclet, Grashof and surface tension Reynolds numbers were calculated to understand the importance of heat transfer by convection and the roles of various driving forces in the weld pool. In order to validate the model, welding experiments were conducted under several welding currents. The predicted weld pool dimensions were compared with the corresponding experimental results, and good agreement between simulation and preliminary test results was achieved.
基金Project was supported by National Defense Basic Scientific Research Program of China (JCKY2016205A001)。
文摘By measuring and analyzing infrared thermal image of the specimen in static load tensile test process, it was studied that the influence of the undercut defects and double-sided dressing method on the deformation behavior of the laser welded joint specimens of TC4 titanium alloy. The results showed that for the unmodified specimens, the yield phenomenon occurs first in the region of the joint, but the undercut value has an effect on the stress and strain of starting to yield phenomenon, and a great effect on the plastic deformation behavior.When the undercut is less than a certain value, the large plastic deformation occurs in the base metal region and the plasticity of the specimen is comparable to that of the base metal, but the larger undercut defect results in a concentrated plastic deformation in the joint region and rapidly failed in this region. But the double-sided dressing specimen is significantly different. The physical yield is no longer concentrated in the joint region, but at the same time occurs in the several regions including joint and the base metal. And the plastic deformation mainly occurs in the base material area, similar to that of the base material.
文摘To solve the difficulty in the explosive welding of corrosion-resistant aluminum and stainless steel tubes, three technologies were proposed after investigating the forming mechanism through experiments. Then, a 3D finite element model was established for systematic simulations in the parameter determination. The results show that the transition-layer approach, the coaxial initial assembly of tubes with the top-center-point the detonation, and the systematic study by numerical modeling are the key technologies to make the explosive welding of LF6 aluminum alloy and 1Cr18Ni9Ti stainless steel tubes feasible. Numerical simulation shows that radial contraction and slope collision through continuous local plastic deformation are necessary for the good bonding of tubes. Stand-off distances between tubes (D1 and D2) and explosives amount (R) have effect on the plastic deformation, moving velocity, and bonding of tubes. D1 of 1 mm, D2 of 2 mm, and R of 2/3 are suitable for the explosive welding of LF6-L2-1Cr18Ni9Ti three-layer tubes. The plastic strain and moving velocity of the flyer tubes in-crease with the increase of stand-off distance. More explosives (R2/3) result in the asymmetrical distribution of plastic strain and non-bonding at the end of detonation on the tubes.
基金This work is supported by The Aeronautical Funds of China
文摘The characteristics of temperatures, stresses and strains fields have been studied numerically for a titanium alloy sheet welded with an improved gas tungsten arc welding method, in which a trailing spot heat sink is introduced to control the welding stress and distortion. The impinging jet model is employed to describe the internee heat transfer between the cooling media and the top suufuce of the workpiece. The influcnee of the distance between arc and heat sink is investigated. Results show that there is an ideal range of distance. Using the ideal distance, a low stress and no distortion welding structure can be derived.
文摘Based on the situation of welding thermal conduction and thermo-elasto-platicity research, this paper explores some problems in this field. First, the boundary element method for nonlinear problems is improved by linearization of nonlinear problems and used in welding thermal conduction analysis. Second, the thermo-elasto-plastic finite element method is used for the welding stress calculation, in which the phase transformation is considered by the 'equivalent linear expansion coefficient method'. The comparison of the calculated results with experimental data shows that the methods provided in this paper are available.
文摘A model of double grains under plane stress state has been established. According to the double grain model, thermal stress induced by thermal cycling in welding fusion zone is numerically simulated by finite element method, and the microstructures before and after thermal cycling are observed. The effect of thermal stress on weld microstructure is discussed. Experimental and analysis results show that the difference between the coefficients of thermal expansion and elastic modulus for grains along different crystal directio n can produce alternate thermal misfit stress and strain near boundaries under thermal cycling. At the temperature of upper and lower limit, thermal stress nearby grain boundary reaches maxima. Thermal stress induced changes in microstructure, which expressed by the sending dislocations from boundaries to matrix, piling up against the boundaries and the increasing of dislocation density.
文摘Alloy 690 is a typical Ni-Cr-Fe alloy, which is widely used in nuclear power application. However, filler metal 52M (FM-52M) used in alloy 690 weldment is fimnd to be susceptible to ductility-dip cracking (DDC) , which seriously affects safety and life extension in nuclear application. In this paper, the DDC susceptibility of FM-52M in welding process was investigated using finite element method. At first, Gleeble-based testing technique, strain to fracture ( STF ) test, was used to evaluate the DDC susceptibility and the formation mechanism of DDC was explained. The result shows that FM-52M is most susceptible at 1 050 ℃ and grain boundary weakness at high temperature induces crack initiation. Afterwards, in order to evaluate the DDC susceptibility under complex stress state, tube-plate welding model was built by means of ABAQUS software. Susceptible regions could be confirmed associated with STF results. The simulation result shows that HAZ is the most susceptible region in FM-52M joint.
文摘The role of oxides in the formation of hole defects in friction stir welded joint of 2519-T87 aluminum alloy has been investigated by using optical microscope, scanning electron microscope, electron backscatter diffraction and electron probe microanalyzer to examine the distribution of oxides and the features of hole defects, and using ABAQUS 3D thermo-mechanical coupling finite element model based on arbitrary Lagrangian-Eulerian method to simulate the material flow behavior. Oxides exist at the edge of tunnel hole and in the micropores in the joint. Based on distribution of oxygen and material flow behavior, it is believed that the oxides on the surface of the alloy tend to flow down into the bulk along the flow direction of plastic material during friction stir welding, aggregate in the weak region of material flow at the intersection of the shoulder affected zone and the stir pin-tip affected zone, and consequently prevent the material from contacting and diffusing. Due to the insufficient material flow and therefore the small plastic deformation,the pressure is not high enough to compress the accumulated oxides, resulting in hole defects.
文摘利用裂纹扩展分析方法和质量分类法研究铝合金车体含缺欠焊接结构的疲劳寿命问题。首先,研究IIW:2015的基于Paris定律的裂纹扩展分析的理论基础和BS 7910:2019的基于考虑焊接缺欠质量的S-N曲线的质量分类法的算法原理;其次,归纳总结了这2种方法进行考虑焊接质量的焊接结构疲劳寿命评估流程;再次,在疲劳载荷作用下,基于BS EN 1999-1-3:2007的名义应力法对某动车组铝合金车体进行疲劳分析,确定车体疲劳关切焊缝部位;最后,分别利用裂纹扩展分析方法和质量分类法对车体关切焊缝侧门下角进行考虑初始裂纹的疲劳寿命评估。结果表明:基于质量分类法的剩余寿命为1.4×106次,基于裂纹扩展分析法的剩余寿命为2.64×106次。