A numerical procedure is provided to analyze temperature and residual stress fields in multi-pass TIG welds with different pipe and electrode material. Based on the ABAQUS software and FORTRAN codes, to appraise the temperature fields and the residual stresses over the TIG process, an uncoupled thermo-mechanical, finite element model (FEM) is developed. For considering volumetric thermal flux on the workpiece, the “GOLDACK” method is used. The silent element method is utilized to model the weld deposit. To validate the presented simulation model, the TIG process is performed in two passes on SUS304 stainless steel pipe. Then, the process is modeled for three and four passes to consider the effect of pass number on axial and hoop residual stresses in the outer and inner surfaces of the welded pipes. Additionally, the effects of base material and preheating temperature on the internal and external surface stresses of pipe are investigated. Results show that, the base material type has a greater effect on the tensile axial residual stress of the outer surface rather than that of the inner surface. However, the welding pass number shows no significant influence on the peak of the tensile axial residual stress on the inner surface of the pipe. In terms of preheating, the stress magnitude is reduced by raising the preheating temperature but with more intense in the inner surface of the pipe. Additionally, to keep the tensile axial residual stress below the base metal yield strength, the preheating at least up to 325 °C is essential.

Effects of material type, preheating and weld pass number on residual stress of welded steel pipes by multi-pass TIG welding (C-Mn, SUS304, SUS316)

Finite element based parametric study on the characterization of weld process moving heat source parameters in austenitic stainless steel

A two-dimensional thermomechanical finite element (FE) model of laser surface glazing (LSG) has been developed for H13 tool steel. The direct coupling technique of ANSYS 17.2 (APDL) has been utilised to solve the transient thermomechanical process. A H13 tool steel cylindrical cross-section has been modelled for laser power 200 W and 300 W at constant 0.2 mm beam width and 0.15 ms residence time. The model can predict temperature distribution, stress–strain increments in elastic and plastic region with time and space. The crack formation tendency also can be assumed by analysing the von Mises stress in the heat-concentrated zone. Isotropic and kinematic hardening models have been applied separately to predict the after-yield phenomena. At 200 W laser power, the peak surface temperature achieved is 1520 K which is below the melting point (1727 K) of H13 tool steel. For laser power 300 W, the peak surface temperature is 2523 K. Tensile residual stresses on surface have been found after cooling, which are in agreement with literature. Isotropic model shows higher residual stress that increases with laser power. Conversely, kinematic model gives lower residual stress which decreases with laser power. Therefore, both plasticity models could work in LSG for H13 tool steel.

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Thermomechanical modelling of laser surface glazing for H13 tool steel

Numerical simulation of heat transfer and fluid flow during vacuum electron beam welding of 2219 aluminium girth joints

Composite structures have wide applications in mechanical fields. Such structures consist of several joints, which may run a risk of eventually weakening a structure in case of excessive weight. It is, therefore, necessary to strengthen a structure so as to reduce the chance of failure. The present study was undertaken with a model of tubular T-joint having adhesive fillet. It also focussed on three-dimensional stress analysis on adhesive fillet. The model was made of laminated fibre-reinforced polymer (FRP) composite tubes with adhesive triangular fillet, subjected to axial compressive loading. The modelling and analysis were carried out by using finite element method (FEM) for three different joints with different geometrical parameters. The model was validated by using the available finite element model results. Based on the present finite element model results, the axial stress (σz) at brace-fillet intersection, circumferential stress (σφ) and circumferential-axial stress (τφr) at chord-fillet intersection were found to have greater effect as compared with other stress components. The maximum value of stress component could be noticed in between the brace and the chord joint region, which could eventually cause failures. The effect of adhesive fillet on deflection was studied in details by using ANSYS 18.1, and results showed that deflection of adhesive fillet model could be reduced by 12.36% as compared with non-fillet condition. Based on the present research findings, the presence of adhesive fillet was found to significantly reduce deflection effect as well as improve joint strength and stability of the structure.

Detailed investigation of adhesive fillet tubular T-joint of laminated FRP composite tube under axial compressive load

Weld characteristics of non-axisymmetrical butt welded branch pipe T-joints using finite element simulation and experimental validation

Press-brake bending is one of the important sheet metal forming processes widely used to fabricate different angles and channels in automotive applications. Plastic deformation of material during bending generates elastic stress waves known as acoustic emission (AE), enabling online monitoring of the bending process. The analysis of these stress waves helps in process characterization and aids in the identification of defects. The non-homogeneous plastic deformation that occurs during bending leads to the development of residual stress (RS) in the bend regions after forming. The locked-in residual stresses that remain after bending are measured using the x-ray diffraction method. The present study aims to use the AE technique for online bend monitoring of austenitic stainless steel (SS) of type 304L and correlate the AE parameters acquired during bending with the final locked-in RS present in the bend regions. Toward this, SS 304L sheets were bent to various bend angles, viz. 45°, 60°, 90°, 108°, 120°, and 135°, along the rolling direction and perpendicular to the rolling direction. Among the many AE parameters derived from the analysis of AE signals, it is shown that normalized cumulative counts and energy increase with bend angle. The increase in AE is well correlated with the RS that develops due to plastic deformation. The observed correlations between AE parameters acquired during bending and RS measured after bending are discussed.

Acoustic Emission during Press-Brake Bending of SS 304L Sheets and its Correlation with Residual Stress Distribution after Bending

Effect of cutting process on the stress corrosion susceptibility of AISI 304L stainless steel

Localized heating and cooling during welding introduces residual stress in the weld joints due to the thermal gradients. The microstructure formation in 2.25Cr–1Mo steel is very much sensitive to the rate of cooling and eventually, the austenite may transform to pearlite/bainite/martensite. A variant of Tungsten Inert Gas (TIG) welding called Activated-TIG (A-TIG) welding was made use of in this study. Here, we have tried to develop a numerical model based on the finite element method to predict the thermo-mechanical behavior of 6 mm thick 2.25Cr–1Mo steel weld joints, with accounting solid-state phase transformation. The heat energy supplied to the workpiece is determined and calibrated in the heat source model. Simulated thermal cycle showed a peak temperature of 1377 °C at 8 mm distance away from the weld centerline, whereas, the experimental result showed 1371 °C. A k-type thermocouple was used to measure the temperature distribution during welding. The simulated thermal distributions were sequentially coupled to mechanical analysis. The evolution of stress and ultimately the locked-in residual stresses were determined. X-ray diffraction studies showed the peak residual stress near heat affected zone of 592 MPa and the vertical height gauge was used to measure the distortion before and after welding. The predicted residual stresses and distortion showed good agreement with the experimental measurements.

S. Arun Kumar

Papers

Weld characteristics of non-axisymmetrical butt welded branch pipe T-joints using finite element simulation and experimental validation

Acoustic Emission during Press-Brake Bending of SS 304L Sheets and its Correlation with Residual Stress Distribution after Bending

Effect of cutting process on the stress corrosion susceptibility of AISI 304L stainless steel

Numerical Simulation and Experimental Validation of A-TIG Welding of 2.25Cr–1Mo Steel