Case-Study Inverse Thermal Analyses of Al2139 Laser Welds

Case study inverse thermal analyses of A12139 laser welds are presented. These analyses employ a numerical methodology that is in terms of analytic and numerical basis functions for inverse thermal analysis of steady state energy deposition in plate structures. The results of the case studies presented provide parametric representations of weld temperature histories that can be adopted as input data to various types of computational procedures, such as those for prediction of solid-state phase transformations and their associated software implementations. In addition, these weld temperature histories will be useful for construction of numerical basis functions that can be adopted for inverse analysis of welds corresponding to other process parameters or welding processes whose process conditions are within similar regimes.     

Case-Study Inverse Thermal Analyses of Al2139 and Al2198 Electron Beam Welds

Case study inverse thermal analyses of A12139 and Al2198 electron beam welds are presented. These analyses represent a continuation of previous studies using laser beam welds, but provide accessibility to different regions of the parameter space for temperature histories than achievable using laser beams. For these analyses, a numerical methodology is employed, which is in terms of analytic functions for inverse thermal analysis of steady-state energy deposition in plate structures. The results of the case studies presented provide parametric representations of weld temperature histories, which can be adopted as input data to various types of computational procedures, such as those for prediction of solid-state phase transformations and their associated software implementations. In addition, these weld temperature histories can be used for construction of numerical basis functions that can be adopted for inverse analysis of welds corresponding to other process parameters or welding processes process conditions of which are within similar regimes.     

Inverse Thermal Analysis of Refractory Metal Laser Welds

Case study inverse thermal analyses of Vanadium and Tantalum laser welds are presented. These analyses employ a methodology that is in terms of analytic basis functions for inverse thermal analysis of steady-state energy deposition in plate structures. The results of the case studies presented provide parametric representations of weld temperature histories that can be adopted as input data to various types of computational procedures, such as those for prediction of solid-state phase transformations. In addition, these temperature histories can be used to construct parametric-function representations for inverse thermal analysis of welds corresponding to other process parameters or welding processes process conditions of which fall within similar regimes. This study also discusses specific aspects the inverse-analysis methodology relevant to further development of algorithms for its application in practice.     

Inverse Thermal Analysis of Steel Welds Using Solidification-Boundary Constraints

Inverse thermal analyses of structural steel deep-penetration welds are presented. These analyses employ a methodology that is in terms of numerical-analytical basis functions and constraint conditions for inverse thermal analysis of steady-state energy deposition in plate structures. These analyses provide parametric representations of weld temperature histories that can be adopted as input data to various types of computational procedures, such as those for prediction of solid-state phase transformations and mechanical response. In addition, these parameterized temperature histories can be used for inverse thermal analysis of welds corresponding to other welding processes whose process conditions are within similar regimes. The present study applies an inverse thermal analysis procedure that uses three-dimensional constraint conditions whose two-dimensional projections are mapped within transverse cross sections of experimentally measured solidification boundaries.     

Inverse Thermal Analysis of Ti-6Al-4V Deep-Penetration Welds Using Volumetric Constraints

Case study inverse thermal analyses of Ti-6Al-4V deep-penetration welds are presented. These analyses employ a methodology that is in terms of numerical-analytical basis functions for inverse thermal analysis of steady state energy deposition in plate structures. The results of the case studies provide parametric representations of weld temperature histories that can be adopted as input data to various types of computational procedures, such as those for prediction of solid-state phase transformations. In addition, these temperature histories can be used to construct parametric-function representations for inverse thermal analysis of welds corresponding to other process parameters or welding processes whose process conditions are within similar regimes. The present study applies an inverse thermal analysis procedure that provides for the inclusion of volumetric constraint conditions whose two-dimensional projections are mappings onto transverse cross sections of experimentally measured solidification and transformation boundaries.     

Inverse Thermal Analysis of 21-6-9 Stainless Steel Laser Welds

Case study results of inverse thermal analyses of 21-6-9 stainless steel laser welds are presented in this article. These analyses employ a methodology that is depicted in terms of analytic basis functions for inverse thermal analysis of steady-state energy deposition in plate structures. The results of the case studies presented provide parametric representations of weld temperature histories that can be adopted as input data to various types of computational procedures, such as those for prediction of solid-state phase transformations. In addition, these temperature histories can be used to construct parametric-function representations for inverse thermal analysis of welds corresponding to other process parameters or welding process conditions of which are within similar regimes. The case studies presented also examine specific aspects the inverse-analysis methodology relevant to further development of algorithms for its application in practice.     

Inverse Thermal Analysis of Stainless Steel Deep-Penetration Welds Using Volumetric Constraints

Case-study inverse thermal analyses of 304L, 21Cr-6Ni-9Mn, and Grade EH-36 stainless steel deep-penetration welds are presented. These analyses employ a methodology that is in terms of numerical-analytical basis functions for inverse thermal analysis of steady-state energy deposition in plate structures. The results of the case studies presented provide parametric representations of weld temperature histories that can be adopted as input data to various types of computational procedures, such as those for prediction of solid-state phase transformations. In addition, these temperature histories can be used to construct parametric-function representations for inverse thermal analysis of welds corresponding to other process parameters or welding processes whose process conditions are within similar regimes. The present study extends an inverse thermal analysis procedure applied in previous studies. This extension provides for the inclusion of volumetric constraint conditions whose two-dimensional projections are mappings onto transverse cross sections of experimentally measured solidification boundaries. This study also discusses specific aspects of the inverse-analysis methodology relevant to further development of algorithms for its application in practice.     

Inverse Thermal Analysis of 304L Stainless Steel Laser Welds

An inverse thermal analysis of 304L stainless steel laser welds is presented. This analysis employs a methodology that is in terms of analytical basis functions. The results of this analysis provide parametric representations of weld temperature histories that can be adopted as input data to various types of computational procedures, such as those for prediction of solid-state phase transformations. In addition, these temperature histories can be used to construct parametric-function representations for inverse thermal analysis of welds corresponding to other process parameters or welding processes whose process conditions are within similar regimes. Specific aspects of the inverse-analysis methodology employed that relevant to its understanding and further development are examined.     

Inverse Thermal Analysis of a Titanium Laser Weld Using Multiple Constraint Conditions

Inverse thermal analysis of a titanium laser weld using multiple constraint conditions is presented. This analysis employs a methodology that is in terms of numerical-analytical basis functions for inverse thermal analysis of steady-state energy deposition in plate structures. The results of this type of analysis provide parametric representations of weld temperature histories that can be adopted as input data to various types of computational procedures, such as those for prediction of solid-state phase transformations. In addition, these temperature histories can be used to construct parametric-function representations for inverse thermal analysis of welds corresponding to other process parameters or welding processes whose process conditions are within similar regimes. The present study extends an inverse thermal analysis procedure applied in previous studies. This extension provides for the inclusion of constraint conditions associated with both solidification and phase transformation boundaries.     

Parametric Modeling of Welding Processes Using Numerical-Analytical Basis Functions and Equivalent Source Distributions

A general methodology for inverse thermal analysis of steady-state energy deposition in plate structures, typically welds, is extended with respect to its formulation. This methodology is in terms of numerical-analytical basis functions, which provide parametric representations of weld-temperature histories that can be adopted as input data to various types of computational procedures, such as those for prediction of solid-state phase transformations and mechanical response. The extension of the methodology presented here concerns construction of numerical-analytical basis functions and their associated parameterizations, which permit optimal and convenient parameter optimization with respect to different types of weld-workpiece boundary conditions, energy source characteristics, and experimental measurements adoptable as weld-temperature history constraints. Prototype inverse thermal analyses of a steel weld are presented that provide proof of concept for inverse thermal analysis using these basis functions.     

Analysis of Heat Affected Zone in Welded Aluminum Alloys Using Inverse and Direct Modeling

The concept of constructing parameter spaces for process control and the prediction of properties within the heat affected zone (HAZ) of welds using inverse modeling is examined. These parameter spaces can be, in principle, either independent or a function of weld process conditions. The construction of these parameter spaces consists of two procedures. One procedure entails calculation of a parameterized set of temperature histories using inverse heat transfer analysis of the heat deposition occurring during welding. The other procedure entails correlating these temperature histories with either a specific process control parameter or physical property of the weld that is measurable. Two quantitative case study analyses based on inverse modeling are presented. One analysis examines the calculation of temperature histories as a function of process control parameters. For this case, the specific process control parameter adopted as prototypical is the electron beam focal point. Another analysis compares some general characteristics of inverse and direct modeling with respect to the prediction of properties of the HAZ for deep penetration welding of aluminum alloys. For this case, the specific property adopted as prototypical is hardness. This study provides a foundation for an examination of the feasibility of constructing a parameter space for the prediction of weld properties using weld cross-section measurements that are independent of weld process conditions.     

Inverse Thermal Analysis of Heat-Affected Zone in Al2129 and Al2198 Laser Welds

Case study analyses of A12139 and Al2198 laser welds are presented. These analyses demonstrate the concept of constructing parameter spaces for prediction of properties within the heat-affected zone (HAZ) of welds using inverse modeling, which are in turn for process control. The construction of these parameter spaces consists of two procedures. One procedure entails calculation of a parameterized set of temperature histories by inverse analysis of the heat deposition occurring during welding. The other procedure entails correlating these temperature histories with a specific physical property of the weld that is measurable. The analyses presented here examines some characteristics of inverse modeling with respect to the prediction of hardness within the HAZ for deep penetration laser welding of the Aluminum alloys A12139 and Al2198. This study further demonstrates the feasibility of constructing a parameter space for the prediction of weld properties using weld cross section measurements that are independent of weld process conditions.     

Modifying residual stress levels in rail flash-butt welds using localised rapid post-weld heat treatment and accelerated cooling

Abstract

Flash-butt welding is used in the manufacture of continuously-welded rails. Finished welds typically exhibit high tensile residual stresses in the rail web and at the upper surface of the rail foot, which may increase the risk of fatigue failure in service. An understanding of the influence of the welding process, including post-weld cooling, on the residual stress distribution is necessary to improve the performance of flash-butt welds by post-weld heat treatment (PWHT), since incorrect treatment may have adverse effects on both residual stress and weld material characteristics. A finite element model has been developed to simulate post-weld cooling in flash-butt welded AS60 kg m^–1 rail. Computed thermal histories for normal (air) cooling, rapid PWHT, and accelerated cooling (water spray) were used as inputs to calculate sequentially coupled stress–time histories, including phase transformations. In addition, the localised influence of the initiation time for rapid PWHT, after final upset, on the reduction of tensile residual stresses was investigated. Heating the rail foot immediately after final upset reduced tensile residual stresses in the web region of the weld. Preliminary numerical predictions showed that water quenching the entire weld region too soon after the austenite–pearlite transformation is completed can induce further tensile residual stresses without affecting the microstructure. The results of the numerical analysis can be used to modify the flash-butt welding procedure to lower residual stress levels, and hence improve weld performance.     

Numerical simulation of welding-induced distortion in thin-walled structures

Abstract

A sequentially coupled thermal stress analysis approach is presented for modelling temperature and distortion profiles resulting from welding thin-walled structures. The material is modelled as thermo-elastic–plastic with isotropic strain hardening. The heat source is modelled as a three-dimensional (3-D) double ellipsoid, and 3-D finite element (FE) models are employed for predicting ensuing distortions. Comparisons between the simulation results and experiments performed for eight weld configurations are presented. The weld configurations include bead-on-plate, butt weld and tee joint welds with varying plate thicknesses. Temperature measurements using thermocouples and an infrared (IR) imaging radiometer are directly compared to the thermal simulations. Likewise, distortions measured directly on the experimental set-ups are compared to the FE distortion predictions. Very good correlation is obtained for temperature as well as distortion predictions between experimental and proposed numerical approaches. Lastly, details of a weld simulation for the rear section of a motorcycle frame are presented.     

Relationships between weld parameters,hardness distribution and temperature history in alloy 7050 friction stir welds

Abstract

Aluminium alloy 7050 was friction stir welded using three different ratios of tool rotation rate to weld travel speed. Welds were made using travel speeds of between 0·85 and 5·1 mm s^?1. Weld power and torque were recorded for each weld. An FEM simulation was used to calculate the time–temperature history for a subset of the welds. For each weld the hardness distribution with and without post-weld heat treatment was determined. The hardness distributions within the welds are rationalised based on the friction stir welding parameters and the resulting temperature histories. The analysis provides a basis for manipulation of weld parameters to achieve desired properties.     

Prediction of solidification cracking in laser welds of type 310 stainless steels

The occurrence of solidification cracks in laser welds of type 310 stainless steels was predicted by numerical analyses of the solidification brittle range (ductility curve for cracking) and thermal strain in the weld metal. The solidification brittle range in laser welding was estimated from that in arc welding based on the numerical analyses of supercooling (for calculating dendrite tip temperature) and segregation (for calculating completely solidified temperature) during rapid solidification. The calculated solidification brittle range was reduced with an increase in the welding speed because of the enhanced supercooling and the inhibited solidification segregation. The thermal strain analysis by FEM suggested that solidification cracks would occur in SUS310S welds at laser travelling velocity of 60 mm/s applying the initial strain of 1.5%, while no solidification cracks in SUS310EHP welds at any laser travelling velocities applying the higher initial strain of 2.2%. The cantilever type cracking test in laser welding revealed that the predicted results of occurrence of solidification cracks were consistent with experimental ones.     

激光＋GMAW复合热源焊焊缝成形的数值模拟——I．表征激光作用的体积热源分布模式

为了建立激光＋GMAW电弧复合焊接的体积热源作用模式,根据激光深熔焊接的焊缝形状特征,分析了激光焊接的热源作用特点,提出了4类新的体积热源分布函数．建立了激光焊接温度场的数值分析模型,计算出了4类体积热源模式下的激光焊缝形状尺寸,与实测结果进行了对比．发现提出的4类体积热源模式能够较好地对激光焊接过程中激光热源对焊缝成形的作用进行表征,是恰当的和适用的．     

Evaluation of fracture behavior of the reheated weld zone in API 2W Gr. 50 steel weld metals

In this study the effect of martensite-austenite (M-A) constituents on the fracture behaviour of the reheated weld zone formed by subsequent weld passes in API 2W Gr. 50 steel welds was evaluated. For the weld thermal cycle simulation process with the Geeble thermal simulator, the actual single-pass weldment was used rather than the base metal. The reheated weld zone in the weld metal was categorized into four typical areas according to the peak temperature. The test results indicated that toughness is closely related to the fraction of the martensite-austenite constituents.In particular, the intercritical reheated weld zone with a high fraction of M-A as well as a coarse-grained reheated zone can be considered as local brittle zones of weld metal.     

Effects of thread interruptions on tool pins in friction stir welding of AA6061

In this work, effects of pin thread and thread interruptions (flats) on weld quality and process response parameters during friction stir welding (FSW) of 6061 aluminium alloy were quantified. Otherwise, identical smooth and threaded pins with zero to four flats were adopted for FSW. Weldability and process response variables were examined. Results showed that threads with flats significantly improved weld quality and reduced in-plane forces. A three-flat threaded pin led to production of defect-free welds under all examined welding conditions. Spectral analyses of in-plane forces and weld cross-sectional analysis were performed to establish correlation among pin flats, force dynamics and defect formation. The lowest in-plane force spectra amplitudes were consistently observed for defect-free welds.     

Analysis of processes involving heat deposition using constrained optimisation

Abstract

Aspects are presented of a general approach based on constrained optimisation for the analysis of processes involving heat deposition, such as welding processes. The methodology of the present approach entails generating functions and subdomain elliptic solvers useful for the practical application of constrained optimisation for the calculation of thermal histories. The emphasis in the present work is on the general properties associated with the methodology of this approach as these properties relate to its application. In addition, prototype weld analyses are presented that serve to demonstrate many of the details associated with the practical application of this methodology.