热沉影响钛合金薄板焊接残余应力的试验分析

采用切条应力释放法测量了钛合金TC4薄板常规钨极氩弧焊(GTAW)和动态控制低应力无变形GTAW对接试件中的纵向残余应力和纵向残余塑性应变的分布。测量结果表明,钛合金常规GTAW缝中残余拉应力峰值小于其母材屈服强度,焊缝附近存在残余压缩塑性应变;动态控制低应力无变形GTAW焊技术中热沉的冷却作用使得热源与热沉之间的高温金属承受强烈的拉伸作用,产生拉伸塑性变形,部分抵消了焊接过程中已产生的缩短的塑性变形,使得试件中纵向残余塑性应变减小,焊接残余拉应力峰值降低,残余压应力水平降低。切条应力释放法是一种简便有效的薄板焊后残余应力测量方法,能够满足工程应用的精度要求。     

Trailing heat sink effects on residual stress and distortion of pulsed laser welded Hastelloy C-276 thin sheets

A three-dimensional finite element model (FEM) was established to reveal the thermal-mechanical behaviors of pulsed laser welding (PLW) with and without trailing heat sink. Experiments were carried out to measure the welding temperature histories, residual distortions and solidification profiles. The simulation results agree well with the corresponding experimental measurements. The peak values of the temperature and transient longitudinal tensile stresses valleys in the weld increase as the cooling intensity increases from 5000 to 15,000 W/(m² K), while those of the temperature and transient longitudinal compressive stresses near the weld decrease. The peak values of the longitudinal residual compressive stresses and plastic strains, and the maximum deflections in longitudinal and transverse direction decrease as the cooling intensity increases from 5000 to 15,000 W/(m² K). The magnitudes of the transverse shrinkage distortions increase as the cooling intensity increases from 5000 to 15,000 W/(m² K). The proper cooling intensity to reduce the residual stresses and distortions of the PLW with the trailing heat sink is detected at 10,000 W/(m² K). The trailing heat sink is technically feasible for actual pulsed laser restraint welding in Hastelloy C-276 thin sheet structures.     

Numerical simulation and experimental investigation of temperature and residual stresses in GTAW with a heat sink process of Monel 400 plates

A 3D thermo-mechanical simulation model was developed to predict distributions of temperature and residual stresses during the gas tungsten arc welding (GTAW) process with a heat sink for Monel 400 plates using finite element method. The model was validated against the experimental measurements of both temperature and released strain in the welded plates. Effects of heat input, pipe diameter and water flow rate in the heat sink welding process were investigated. The results showed that in the GTAW process with a heat sink, the high temperature region was only limited to the vicinity of heat source and the maximum temperature of the sample was much lower than that of conventional GTAW process. This resulted in a lower residual stresses and even compressive stresses near the weld zone.     

Stress and distortion mitigation technique for welding titanium alloy thin sheet

Abstract

A stress and distortion mitigation technique for Gas Tungsten Arc Welding (GTAW) of titanium alloy Ti–6Al–4V thin sheet is presented. The proposed welding technique incorporates a trailing heat sink (an intense cooling source) with respect to the welding torch, and it is also called the Dynamically Controlled Low Stress No-Distortion (DC-LSND) technique. The development of this mitigation technique is based on both detailed welding process simulation using the advanced finite element technique and systematic laboratory experiments. The finite element method is used to investigate the detailed thermomechanical behaviour of the weld during conventional GTAW and DC-LSND GTAW. With detailed computational modelling, it is found that by the introduction of a heat sink at some distance behind the welding arc, a saddle shaped temperature field is formed as a result of the cooling effects of the heat sink; the lowest temperature exists in the zone where the heat sink is applied. High tensile action on the surrounding zone is generated by abrupt cooling and contraction of the metals beneath the heat sink, which increases the tensile plastic strain developed during the cooling process and decreases the compressive plastic strain developed in the heating process, and therefore mitigates the residual stresses and plastic strains within and near the weld. The experimental results confirmed the effectiveness of the DCLSND technique and the validity of the computational model. With a proper implementation of the DC-LSND technique, welding stress and distortion can be reduced or eliminated in welding titanium alloy Ti–6Al–4V thin sheet, while no appreciable detrimental effects are caused on the mechanical properties of welded joints by applying the heat sink in the GTAW process.     

钛合金带热沉钨极氩弧焊中热沉作用

采用数值模拟和实验相结合的方法研究了钛合金TC4薄板常规及带热沉的钨极氩弧焊焊接过程中温度及应力应变的分布,考察了热沉对温度场和应力应变场的影响规律,探讨了使用该技术实现应力和变形控制的机理.结果表明:带热沉的钨极氩弧焊焊接过程中,紧随热源之后热沉急冷作用使得试件形成马鞍形温度场,而热沉作用部位温度最低.热沉作用部位的急冷收缩对周围金属产生拉伸作用,使得焊缝及近缝区金属升温过程中产生的压缩塑性应变减小,冷却过程中产生的拉伸塑性应变增大,接头中不协调应变减小,残余应力降低.实验测量与有限元模拟结果吻合良好,证实了采用热沉控制应力与变形的有效性和有限元模型的正确性.     

钛合金薄板带热沉的TIG焊温度场

采用数值模拟和试验相结合的方法比较研究了钛合金薄板常规钨极氩弧焊(TIG)及带热沉的TIG焊焊接过程中温度场的形态与演变历史。相对于预置温度场的静态焊接应力和变形控制技术,带热沉的TIG焊接技术又称动态控制低应力无变形焊接技术(DC-LSND,Dynamically controlled low stress no-distortion)。该技术中。在热源之后紧随起冷却作用的热沉装置。研究结果表明。采用DC-LSND技术在热沉附近形成了中间低两边高的马鞍形温度场,热沉作用部位存在温度低谷,该温度区冷却收缩造成对附近高温区的拉伸作用,使焊缝不协调应变减小,焊缝中的残余拉应力降低,防止了焊接变形的产生。对DC-LSND畸变温度场的研究是了解这种方法控制变形机理的前提。     

Simulations in multipass welds using low transformation temperature filler material

Transient thermal and residual stress fields in flux-cored arc welds were examined using a finite element (FE) model. Experimental multipass welds were produced using both conventional and low transformation temperature (LTT) filler metals. Temperature-dependent material properties and both convective and radiant heat loss boundary condition have been considered in the FE model. The effects of the transformation temperature and interpass intervals on residual stresses were examined. It was found that compressive longitudinal residual stresses were developed at the weld centreline in the LTT filler metal. A short-time interpass interval causes the weld fusion zone to be above the martensite start temperature allowing the optimal use of the phase transformation effect. The FE model is sensitive to alteration in welding parameters and can satisfactorily predict the residual stress distribution in welded parts.     

Numerical simulation of DE-GMAW of magnesium alloy cylinder

Double-electrode gas shielded arc welding( DE-GMAW) was used to weld the magnesium alloy cylinder with the diameter of 200 mm and the thickness of 6 mm. In order to study the residual stress distribution of AZ31 B magnesium alloy welding point,numerical simulation of welding temperature field,stress field and residual stress were carried out by MSC. marc software. The results show that the residual stress in the weld and the heat affected zone is large,and with the increase of the distance away from the weld center,the residual stress decreases. In most areas,the longitudinal residual stress is greater than the transverse residual stress( except for the inside and outside surfaces of the weld),all of which provides theoretical support for the study of magnesium alloy welding residual stress.     

不同退火条件下304L不锈钢埋弧焊接头组织及性能分析

采用埋弧焊方法,进行了304L不锈钢厚板的对接试验研究.通过对焊接接头处的组织观察,并结合焊接接头的-196 ℃冲击韧性以及不同退火条件下残余应力测试,分析了埋弧焊304L不锈钢焊接接头组织和性能. 结果表明,热影响区组织为奥氏体,焊缝区则为奥氏体与少量的铁素体的复相组织;采用残余应力盲孔释放测量方法对焊接接头进行测试,随着退火温度的升高,焊缝及热影响区的残余应力得到进一步的释放;冲击试验中,热影响区-196 ℃冲击吸收能量随退火温度的升高急剧下降,焊缝区-196 ℃冲击吸收能量则呈平稳下降趋势.     

Investigation of the stability of melting and electrode metal transfer in consumable electrode arc welding using power sources with different dynamic characteristics

The results of investigations carried out to study the effect of the dynamic characteristics of power sources on the stability of melting and electrode metal transfer to the weld pool in consumable electrode arc welding are presented. It is shown that when using a new generation of welding inverter power sources the heat and mass characteristics change and this has a decisive effect on the heat content of the weld pool, reduces the level of residual stresses in the heat-affected zone (HAZ) and also increases the susceptibility to reducing the size of structural components in the zone of permanent welded joints.     

Study on stress and deformation of keyhole gas tungsten arc-welded joints

Keyhole gas tungsten arc welding(K-TIG)of Q345 low alloy steel plates was simulated by using SYSWELD software.The temperature field of the K-TIG welding process was simulated with three different combined heat sources and was compared with the weld profile that was obtained experimentally.The temperature field that was obtained by a combination of a double ellipsoid heat source on the upper half and a three-dimensional Gauss heat source on the lower half was similar to the real situation.The effects of plate thickness,gap and welding speed on the deformation and stress of the K-TIG welded joints were investigated by K-TIG welding numerical simulation.A reduction in the thickness of the weld plates reduced the z-direction deformation and transverse residual stress;an appropriate gap reduced the residual stress and an increase in the welding speed reduced deformation after welding,but did not help to control the residual stress after welding.     

Numerical and experimental study of the microstructural evolution and the properties of joints welded on rebars using the GMAW process

This paper is a study of CA-50 rebars from SAE steel grade 1026. This study was carried out in order to improve the control of the mechanical properties of welded joints. Knowing certain variables are very important when it comes to finding the ideal welding parameters and the respective microstructural results, and consequently for the mechanical properties of welded joints. In order to carry out this study, a study of the material as received was carried out in order to establish a solid basis for comparison. The material was welded using argon as the shielding gas with 20% carbon dioxide. The wire used was copper-covered ER70S-6, and the welded joints were lap joints. The temperature was monitored using thermocouples for two different heat inputs. A numerical computer code was developed to simulate the phenomena that occur during the process (temperature gradient, phase transformations and heat transfer). The welded joints did not introduce martensite as a brittle phase, the weld metal had a dendritic structure, the heat-affected zone (HAZ) had two different zones with different grain sizes. All of this was due to the temperature gradient, which also led to different characteristics in the weld bead, HAZ, phases formed and different grain sizes.     

Numerical and experimental study of thermally induced residual stress in the hybrid laser-GMA welding process

A model based on a double-ellipsoidal volume heat source to simulate the gas metal arc welding (GMAW) heat input and a cylindrical volume heat source to simulate the laser beam heat input was developed to predict the temperature field and thermally induced residual stress in the hybrid laser-gas metal arc (GMA) welding process. Numerical simulation shows that higher residual stress is distributed in the weld bead and surrounding heat-affected zone (HAZ). Effects of the welding speed on the isotherms and residual stress of the welded joint are also studied. It is found that an increase in welding speed can reduce the residual stress concentration in the as-weld specimen. A series of experiments has been performed to verify the developed thermo-mechanical finite element model (FEM), and a qualitative agreement of residual stress distribution and weld geometrical size is shown to exist.     

Occurrence of bay area in submerged arc welds

Abstract

An experimental study has been carried out to evaluate the effect of submerged arc welding parameters on the formation of a bay area in the heat affected zone of bead on plate welds in ASTM A36 steel. It was observed that the formation of weld beads having a bay area is influenced by the heat distribution from the arc, which in turn is determined by the welding conditions. The effect of the welding parameters on the weld bead formation is discussed in terms of the arc operation modes and the resulting heat distributions.     

Numerical Simulation and Experimental Investigation of Residual Stresses in the Circumferential Butt GTAW of Incoloy 800H Pipes

The residual stresses developed during the circumferential butt gas tungsten arc welding (GTAW) process of Incoloy 800H pipes were simulated using the finite element method. A decoupled thermostructural model was developed in three dimensions. The element birth and death technique was used for the addition of filler material in the weld pool. The Goldak double ellipsoidal model was used to simulate the distribution of arc heat during welding. The plastic behavior of the material was described by Von Mises yield function and the bilinear kinematics hardening was assumed. To validate the thermostructural model, both temperature and residual stress distributions within the pipes were measured using thermocouples and strain gages, respectively. Good agreements were found between the experimental and simulation results. The model was then used to predict distribution of residual stresses during the GTAW of Incoloy 800H pipes and to study effects of process parameters on the residual stresses.     

Numerical modelling and experimental determination of temperature distribution during manual metal arc welding

Abstract

Welding is a highly reliable and efficient metal joining process. Manual metal arc (MMA) welding is very widely used in industry. The temperature distribution that occurs during welding affects the material microstructure, hardness, and the residual stresses present in the material after welding. In the present work, the temperature distribution during bead on plate welding using MMA welding was experimentally determined for AISI type 304 stainless steel plates and low carbon steel plates of thickness 6 and 12 mm. A three-dimensional computer model based on the control volume method has been developed to predict the temperature distribution in the heat affected zone (HAZ) and in the base plate region of the bead on plate welds, using the weld parameters as input data to the computer model. In this computer model, the heat energy used to melt the electrode is considered as a separate heat flux term and the remaining heat supplied by the welding arc is considered as another heat flux term. A good match between the experimental results and the theoretical predictions was obtained. Using the computer model, the time taken to cool from 800 to 500°C in the coarse grained HAZ (close to the fusion line) of low carbon steel specimens was calculated. From this cooling time and the chemical composition of the material, the maximum hardness in the coarse grained HAZ was predicted. Microhardness measurement in the same region of the welded plates was carried out. The experimentally measured values and predicted results match closely.     

GTAW熔池形状数值模拟精度的改进

采用高斯分布或双椭圆分布热源模式对GTAW熔池形状的数值模拟中发现,计算得到的熔池尾部形状与实际情况有较大差别.文中分析了误差产生原因,提出了数值模拟程序设计中如何确定热源在工件上作用区域计算半径的三个原则.解决了计算结果中熔池尾部后拖不足的问题,提高了GTAW熔池形状数值模拟精度.     

Temperature,macrostructure and hardness in high strength low alloy steel welds

Abstract

A series of welds have been fabricated in high strength low alloy steel (HSLA100) plate by gas metal arc welding at heat inputs of 1.0, 1.6 and 2.2 kJ mm^-1. Slices from the welds were then polished and the macrostructure was observed. Hardness maps were then determined over the entire weld zone, including the heat affected zone and the base plate. Correlations were then made between the hardness maps and the macrostructure. A bead on plate weld was made using the same heat inputs and was used to determine the temperature regimes in the weld as well as thermal profiles of the weld region. Relationships showing good correlations were observed between the various microstructures, the macrostructure, the calculated thermal profiles, and the hardness values.     

K-TIG焊接接头的应力与变形

采用SYSWELD软件对Q345低合金钢板的匙孔型钨极气保焊（keyhole gas tungsten arc welding,K-TIG）焊接过程进行了模拟,选用了3种形式的组合热源对K-TIG焊接过程的温度场进行数值模拟,并与实际焊缝轮廓进行对比,发现采用上半部分双椭球热源和下半部分3D高斯热源的组合热源所得温度场与实际情况较为相似.并通过K-TIG焊接数值模拟,分别研究板厚、间隙和焊接速度对K-TIG焊接接头变形和应力的影响.结果表明,减小焊接板厚有利于减小焊后z向变形和横向残余应力,留出适当的间隙有利于减小焊后残余应力,增大焊接速度有利于减小焊后变形,但不利于控制焊后残余应力.     

数值模拟和实验研究Ti6Al4V合金激光熔透焊接残余应力

采用热-弹塑性三维有限元法研究激光熔透焊接Ti6Al4V合金的残余应力,并采用小孔法测量焊接残余应力以和计算结果进行比较.有限元计算时,建立了以焊缝形貌尺寸为参数的统一锥形热源模型来模拟不同热输入时的焊接温度场,并讨论了边界条件和有限元网格大小的确定.研究结果表明:采用焊缝轮廓尺寸作为热源参数能准确模拟焊缝横截面轮廓;钛合金激光熔透焊接的纵向残余应力分布梯度陡;在焊件表面和内部残余应力分布趋势不同,采用小孔法测量的残余应力分布和计算的焊接件内部残余应力分布相似.