Finite Element Analysis of Modeling Residual Stress Distribution in All-position Duplex Stainless Steel Welded Pipe

On the basis of the thermal-elastic-plastic theory, a three-dimensional finite element numerical simulation is performed on the girth welded residual stresses of the duplex stainless steel pipe with ANSYS nonlinear finite element program for the first time. Three-dimensional FEM using mobile heat source for analysis transient temperature field and welding stress field in circumferential joint of pipes is founded. Distributions of axial and hoop residual stresses of the joint are investigated. The axial and the hoop residual stresses at the weld and weld vicinity on inner surface of pipes are tensile, and they are gradually transferred into compressive with the increase of the departure from the weld. The axial residual stresses at the weld and weld vicinity on outer surface of pipes is compressive while the hoop one is tensile. The distributions of residual stresses compared positive-circle with negative-circle show distinct symmetry. These results provide theoretical knowledge for the optimization of p     

Effect of Post-weld Heat Treatment on Microstructure and Fracture Toughness of 30CrMnSiNi2A Steel Welded Joints

The electron beam local post-weld heat treatment (EBLPWHT) is a rather new method that provides the advantages of high precision, flexibility and efficiency, energy saving and higher productivity. This paper studies the effect of two post-weld heat treatment processes on the microstructure, mechanical properties and fracture toughness of an electron beam welded joints in 30CrMnSiNi2A steel. EBLPWHT, in a vacuum chamber, immediately after welding and a traditional furnace whole post-weld heat treatment (FWPWHT) were compared. The experimental results show that, after EBLPWHT treatment, the main microstructure of weld was changed from coarse acicular martensite into lath rnartensite, HAZ was changed from lath martensite, bainite into lower bainite, and base metal was changed from ferrite and pearlite into upper bainite and residual austenite. The microstructures of different zones of joints in FWPWHT condition were tempered sorbite. The properties of welded joints can be improved by the EBLPWHT in some extent, and especially largely for the fracture toughness of welded joints. However the value of fracture toughness of base metal is comparatively low, so appropriate heat treatment parameters should be explored in the future.     

Improvement of Weld Quality Using a Weaving Beam in Laser Welding

This paper describes a way to improve the weld quality through suppressing the porosity formation and restraining the growth of columnar grains by using a weaving beam in laser welding. The experimental results show that the N2 porosity of beam-weaving laser welding low carbon steel can be remarkably reduced with increasing weaving frequency, and porosity can be eliminated when the weaving amplitude is only 0.5 mm; and the Ar porosity in the weld metal is decreased with increasing weaving frequency and amplitude when the welding speed is higher than 0.5 m/min. The beam-weaving laser welding of ultra-fine grained steel has been investigated. The experimental results show that beam-weaving laser welding with appropriate amplitude and frequency can partly restrain the growth of the columnar grain and improve the tensile strength of the weld metal.     

Friction Stir Welding of Al Alloy Thin Plate by Rotational Tool without Pin

For friction stir welding (FSW), a new idea is put forward in this paper to weld the thin plate of Al alloy by using the rotational tool without pin. The experiments of FSW are carried out by using the tools with inner-concave-flute shoulder, concentric-circles-flute shoulder and three-spiral-flute shoulder, respectively. The experimental results show that the grain size in weld nugget zone attained by the tool with three-spiral-flute shoulder is nearly the same while the grain sizes decrease with the decrease of welding velocity. The displacement of material flow in the heat-mechanical affected zone by the tool with three-spiral-flute shoulder is much larger than that by the tool with inner-concave-flute shoulder or concentric-circles-flute shoulder. The above-mentioned results are verified by numerical simulation. For the tool with three-spiral-flute shoulder, the tensile strength of FSW joint increases with the decrease of welding velocity while the value of tensile strength attained by the welding velocity of 20 mm/min and the rotation speed of 1800 r/min is about 398 MPa, which is 80% more than that of parent mental tensile strength. Those verify that the tool with three-spiral-flute shoulder can be used to join the thin plate of Al alloy.     

Thermal Residual Stresses in W Fibers/Zr-based Metallic Glass Composites by High-energy Synchrotron X-ray Diffraction

Thermal residual stresses in W fibers/Zr-based metallic glass composites were measured by in situ high energy synchrotron X-ray diffraction(HEXRD). The W fibers for the composites were 300,500,and 700 m m in diameter,respectively. Coaxial cylinder model(CCM) and finite element model(FEM) were employed to simulate the distribution of thermal residual stress,respectively. HEXRD results showed that the selected diameters of W fiber had little influence on the value of thermal residual stresses in the present composites. Thermal residual stresses simulated by CCM and FEM were in good agreement with HEXRD measured results. In addition,FEM results exhibited that thermal residual stress concentrated on interface between the two phases and area where the two W fibers were the closest ones to each other.     

Thermal Residual Stresses in Multilayered Coatings

The mechanical integrity and reliability of coated devices are strongly affected by the residual stresses in thin films and coatings. However, due to the metallurgical complexity of materials, it is rather difficult to obtain a closed-form solution of residual stresses within multilayered coatings (e.g. functionally graded coatings, FGCs). In this paper, an analytical model is developed to predict the distribution of residual stresses within multilayered coatings. The advantage of this model is that the solution of residual stresses is independent of the number of layers. Specific results are obtained by calculating elastic thermal stresses in ZrO2/NiCoCrAIY FGCs, which consist of different material layers. Furthermore, the residual stress distribution near the edges and the stress-induced failure modes of coating are also analyzed. The topics discussed provide some insights into the development of a methodology for designing fail-safe coating systems.     

Microstructure and Mechanical Properties of Electron Beam Welded Alloy J75

Microstructure and mechanical properties of electron beam post-weld aging treatment （PWAT） conditions. The results welded alloy J75 were studied under as-welded and showed that high-quality welds were produced by electron beam welding. Under as-welded condition, a fine dendritic structure consisting of gamma dendrite matrix and Laves phase was observed in the welds. Better mechanical properties were obtained in the weld zone than that of base metal because of the fine size of the dendritic structure. After PWAT, a discontinuous distribution of γ＇ particles existed in the dendritic structure. The presence of a γ＇ depletion zone in the dendrite core resulted in a significant degradation of mechanical properties of the weld.     

Residual Stresses and Deformation Behaviour in a SiC_p/Al Composite

Experiments were conducted to determine theresidual stresses with X-ray diffraction in the ma-trix of a SiC/Al composite after different thermaltreatments,and to investigate the stress-straincharacteristics and fracture behaviour of the com-posite.It was found that there existed a tensileresidual stress in the matrix and both thermal cy-cling between room temperature and 350℃ and lowtemperature treatment in liquid nitrogen reducedthe residual stress.The results of the strengthdifferential effect and Bauschinger effect were con-sistent with the results of residual stressmeasurements.The tensile residual stresses in the Almatrix enhanced the strength differential effect.Themagnitude of Bauschinger effect is greater for a testinitially started in compression than that in tension.     

Microstructure evolution and mechanical properties of linear friction welded S31042 heat-resistant steel

S31042 heat-resistant steel was joined by linear friction welding(LFW) in this study. The microstructure and the mechanical properties of the LFWed joint were investigated by optical microscopy, scanning electronic microscopy, transmission electron microscopy, hardness test and tensile test. A defect-free joint was achieved by using LFW under reasonable welding parameters. The dynamic recrystallization of austenitic grains and the dispersed precipitation of NbCrN particles resulting from the high stress and high temperature in welding, would lead to a improvement of mechanical property of the welded joint.With increasing the distance from the weld zone to the parent metal, the austenitic grain size gradually increases from ~1μm to ~150μm, and the microhardness decreases from 301 HV to 225 HV. The tensile strength(about 731 MPa) of the welded joint is comparable to that of the S31042 in the solution-treated state.     

Microstructure and Mechanical Properties of Electron Beam Welded Titanium Alloy Ti-6246

Electron beam welding(EBW) was applied to a 10-mm-thick plate cut from Ti-6246 compressor disk.The microstructural characteristics, microhardness and room temperature tensile properties were investigated. Microstructure observations indicated that there existed plenty of thin needle-like α platelets studding in the matrix of the columnar β grains in the as-welded fusion zone(FZ). Post-weld heat treatment(PWHT) led to the precipitation of small secondary α platelets in the β matrix in heat affected zone and FZ. The thickness and the density of α platelets increased as the temperature of PWHT increased from545 to 645°C. The microhardness across the Ti-6246 EBW joint exhibited a nonuniform distribution. The hardness increased with the decrease of distance to the weld center, and reached the maximum of 467 HV in FZ when PWHT was carried out at 595°C. All the weldments tested with tension were fractured at the base material(BM) and exhibited a ductile fracture mode. The major deformation barrier in BM was the platelet α/β interfaces, however, the major deformation barrier in FZ was found to be β grain boundaries and secondary α/β interfaces. The BM with thicker platelet α phases had lower strength than the other two zones in the joint, and the BM deformed first and led to fracture in this zone.     

Numerical simulation on bucking distortion of aluminum alloy thin-plate weldment

In this paper, the welding residual distortion of aluminum alloy thin plates is predicted using the elasticity-plasticity finite element method (FEM). The factors contributing to the welding buckling distortion of thin plates are studied by investigating the formation and evolution process of welding stresses. Results of experiments and numerical simulations show that the buckling appearance of thin-plate aluminum alloy weldments is asymmetrical in the welding length direction, and the maximum longitudinal deflection appears at the position a certain distance from the middle point of the side edge towards the arc-starting end. The angular deformation direction of thin-plate weldments is not fixed, and such case as the angular deformation value of the arc-starting end being higher than that of the arc-blowout end exists.     

Thin Gauge Titanium Manufacturing Using Multiple-Pass Electron Beam Welding

The optimum processing conditions for joining thin sheet materials (1-3.2 mm) of commercial purity titanium and Ti-6%Al-4%V by electron beam welding were determined by using single- and double-pass melting sequences. For commercial purity titanium weldments, the tensile properties were observed to be similar to the parent material and independent of the sheet thickness and the welding procedure. However, for Ti-6%Al-4%V, the processing conditions during welding were observed to change the characteristics of the alpha lamellae spacing and plate thickness, which in turn influenced the properties. Hence, for joining alpha-beta titanium alloys with use of electron beam welding, the definition of critical processing conditions enables optimization of the structure-property characteristics of the joint.     

钛合金平板电子束焊接残余应力的小孔法测量

采用小孔法对TC11平板真空电子束焊接接头的残余应力进行了测量,结果发现,其残余应力为以纵向残余应力为主的单向拉伸应力状态,横向残余应力数值较小,同时还将测量结果与有限元结果进行对比分析,证明了有限元模型的合理性和可靠性。     

Nutzung von Low‐Transformation‐Temperature‐Werkstoffen (LTT) zur Eigenspannungsreduzierung im Elektronenstrahlschweißprozess

Low‐Transformation‐Temperature materials (LTT) were designed to reduce delay as well as residual tensile stress in welds on carbon‐manganese steels. Using the volume expansion effect during a martensitic transformation these materials counteract the volume shrinkage during cooling. While this positive effects on residual stress relief by Low‐Transformation‐Temperature‐alloys has been proven in various studies, these alloys have always been used in large volumes as additional filler material in electric arc welding processes. Modular heat fields initiated by an electron‐beam‐welding‐process offers the potential of a time‐activated initiation of compressive stresses triggered by phase transformation of Low‐Transformation‐Temperature‐alloys. Developing a technology able to reduce residual stress and thus the deformation of complex welded components is the aim. The first approach of Low‐Transformation‐Temperature‐material used in the electron beam process and its behaviour is presented here.     

Using FEM to determine the thermo-mechanical stress in tube to tube–sheet joint for the SCC failure analysis

The stress corrosion cracking in a weld of the tube to tube–sheet region of heat exchangers is a common problem. Thermo-mechanical stress in tube to tube–sheet joints including welding effect should be determined in this situation for failure analysis. In this paper, the Finite Element Method (FEM) is used to predict the thermo-mechanical stresses including welding residual stress in a tube to tube–sheet weld. Both the thermo-mechanical stress distribution with and without the welding residual stress have also been investigated by numerical simulation. The welding, operating temperature, and operating pressure have effect on total stresses. Especially, the welding residual stresses play an important role in total stress state in tube to tube–sheet joints. Geometric discontinuities of the vicinity of gap cause the welding joint to experience a local stress concentration. A high tensile stress in the tube to tube–sheet region has been demonstrated by FEM, which is the stress aspect for the SCC phenomenon of austenitic stainless steel in chloride environment.     

Influences of deposition rate and oxygen partial pressure on residual stress and microstructure of YSZ thin films

Yttria-Stabilized Zirconia (YSZ) thin films were deposited on borosilicate crown glass substrates using electron beam evaporation technique and controlling technological parameters: deposition rate and oxygen partial pressure. Spectrophotometry, optical interferometry and X-ray diffraction were used to investigate how the thin film optical properties, residual stresses, and structure depend on these parameters. The results showed that the deposition rate had a significant influence on the increase of the refractive index of YSZ thin films while the oxygen partial pressure had less influence on it. In all samples, the tensile stress increased with the increasing of deposition rate and the decreasing of oxygen partial pressure. Meanwhile, all deposited films were poly-crystallizations, while crystallite size and preferential orientation of YSZ thin films changed as a function of deposition rate and oxygen partial pressure. The variations of the optical spectra and residual stress corresponded to the evolution of the film structures induced by the deposition parameters.     

Finite element evaluation of residual stresses in thick plates

This paper makes use of the Finite Elements Method (FEM) to study and analyze residual stresses in the cold bending and welding of thick plates. The welding model consists of two steps: first, performing of the thermal transient analysis model; and second, the carrying out of the mechanical transient analysis based on the temperature pattern at each node on each particular time. Used in these models is the inelastic temperature-dependent material. The output of the model includes residual stresses and permanent distortion; these were then compared with verified experimental results. The validated model and the results exhibit satisfactory agreement up to a 15-percent difference. As for the cold bending of thick plates, it is modeled using another finite element model and the residual stresses and permanent curvature of the thick plates are computed numerically. Again, the FEM model was validated against some official experimental results and satisfactory agreement between them was observed. Finally, the effects of these two different sources of residual stresses were combined, the combined effects established, and the results then discussed.     

Finite element analysis of laser beam-welded butt joints

Thermal distortion of tailored blanks (TBs) during welding usually leads to a poor formability in the subsequent plastic deformation of TBs, and the welding distortion becomes especially serious in TBs consisting of different thickness plates. In this investigation, finite element method was applied to investigate the welding distortion of TBs with different thickness plates produced by laser beam welding. At the beginning, a 3D heat source model was built and verified by experimental results. Then, the following simulation results showed that the residual stresses generated in the thick plate side of the TBs were higher than those in the thin one. The varied reduction of heat input along the thickness direction for those two base plates can explain for this.