Development of life assessment procedures for power plant headers operated under flexible loading scenarios

Investigation of the temperature distribution law in molten pool during the laser cladding process and the varying principle of the forming parts’ cross section sizes to obtain optimum process parameters is essential to improve the precision of deposited parts. In this paper, a three-dimensional numerical single-track processing prediction model (STPPM) in laser cladding was established. The Gaussian distribution heat source was applied. Based on the element birth and death method, the transient temperature field and the geometry of the cladding could be calculated simultaneously by considering the temperature rise of the powder particles, laser energy attenuation and the material phase transition. With the prediction error less than 6.6% for track width and track height, approximately 3.1% for the maximum temperature, numerical simulation results of the track profile agreed well with the experiment results for 316 stainless steel material, indicating the validity of the STPPM. The effects of laser power and scanning speed on the geometry and temperature distribution of cladding were analyzed on the basis of the STPPM and experimentally proved. The results show that track height, width and the temperature in molten pool decreased accordingly with the increase of scanning speed. In addition, track width and the temperature in molten pool increased with the laser power while the track height stabilized. Research in this paper would contribute to minimizing the number of tentative experiments in laser cladding process and the experimental costs, meanwhile improving deposition efficiency during the processing.

Numerical simulation and experimental investigation on three-dimensional modelling of single-track geometry and temperature evolution by laser cladding

Influence of heat input in microwelding of titanium alloy by micro plasma arc

Distortion and residual stresses in thick plate weld joint of austenitic stainless steel: Experiments and analysis

In this paper, investigation of residual stress and distortion induced in 3 mm thick Modified 9Cr-1Mo steel plates during GTA welding is carried out. SYSWELD software is used for the thermo-mechanical analysis. A 3D meshed model is created for the simulation and double ellipsoidal heat source distribution is used for the thermal analysis. Thermal cycles predicted near the fusion zone are compared with experimentally measured thermal cycles using thermocouples. Predicted residual stress profile across the fusion zone is compared with the measured profile using X-ray diffraction method. There is a good agreement between measured and predicted thermal cycles and residual stress profile. Distortion of the weld joint is measured using vertical electronic height gauge. Finite element analysis of distortion of the weld joint is carried out by applying both large and small distortion theories. Comparison of experimental and numerical results showed better accuracy if large distortion theory is applied.

Experimental and finite element analysis of residual stress and distortion in GTA welding of modified 9Cr-1Mo steel

Due to increases in computational power, the finite-element (FE) method is now widely used to predict the thermal, material, and mechanical effects of welding. Welding simulations can provide important information about component distortions and residual stresses. This facilitates a reduction in lead-time and cost associated with the process planning. Moreover, welding is generally performed in combination with other manufacturing processes such as stress relief heat treatment. This article presents a simple method where welding and post weld heat treatment operations are combined using an uncoupled plasticity—creep model. Two FE codes, welding-function-specific SYSWELD and the general-purpose FE package, ABAQUS, were used to perform butt joint welding and post weld heat treatment simulations of two Inconel 718 plates. The predicted results obtained from the two FE codes, such as thermal histories, residual stresses, nodal displacements, and stress relaxation, are compared. Based on the results presented,...

Combined Butt Joint Welding and Post Weld Heat Treatment Simulation Using SYSWELD and ABAQUS

This paper describes high temperature cyclic and creep relaxation testing and modeling of a high nickel-chromium material (XN40F) for application to the life prediction of superplastic forming (SPF) tools. An experimental test program to characterize the high temperature cyclic elastic-plastic-creep behavior of the material over a range of temperatures between 20°C and 900°C is described. The objective of the material testing is the development of a high temperature material model for cyclic analyses and life prediction of SPF dies for SPF of titanium aerospace components. A two-layer viscoplasticity model, which combines both creep and combined isotropic-kinematic plasticity, is chosen to represent the material behavior. The process of material constant identification for this model is presented, and the predicted results are compared with the rate-dependent (isothermal) experimental results. The temperature-dependent material model is furthermore applied to simulative thermomechanical fatigue tests, designed to represent the temperature and stress-strain cycling associated with the most damaging phase of the die cycle. The model is shown to give good correlation with the test data, thus vindicating future application of the material model in thermomechanical analyses of SPF dies for distortion and life prediction.

Experimental and Numerical Characterization of the Cyclic Thermomechanical Behavior of a High Temperature Forming Tool Alloy

Finite element modelling of the experimentally obtained parametric envelopes for stable keyhole plasma arc welding was performed using a three-dimensional conical Gaussian heat source. Uncoupled steady-state and transient heat transfer analyses were performed to predict fusion zones and thermal histories. The heat source definition was validated against the experimentally obtained macrograph and thermal history for a representative stable keyhole condition. The paper investigates the relationships between the primary welding parameters, i.e. current, traverse speed, plasma gas flow rate and the weld efficiency, using inverse finite element modelling. The effect of the change of plasma gas flow rate on weld efficiency was estimated by iteratively changing the efficiency to match the experimental results. The numerical–experimental approach is proposed to establish relationships between welding parameters and weld efficiency which can be utilised to understand the underlying physics of keyhole plasma arc we...

Finite element-based analysis of experimentally identified parametric envelopes for stable keyhole plasma arc welding of a titanium alloy:

Finite element (FE) simulation of welding processes enables the prediction of component distortions which significantly reduces the need for physical trials. This facilitates reduction in lead time and costs associated with process planning. In this paper, FE modelling of tungsten inert gas welding is performed using SYSWELD for a butt joint between 2 mm thick stainless steel 304 (SS304) sheets. A three-dimensional double ellipsoid (Goldak) heat source is used to model the heat flow during welding. The heat source definition as validated against an experimentally obtained grain structure (macrograph) and thermal history. The isotropic hardening material behaviour model is used in the mechanical analysis and the annealing is considered at 1300 °C. FE-predicted distortion for an unclamped situation is compared with an experimental trial. The FE-predicted fusion zone, thermal histories, and residual distortion are found to be in reasonably good agreement with experimental results. The validated FE methodolog...

Finite-element-based parametric study on welding-induced distortion of TIG-welded stainless steel 304 sheets:

SPF tool distortion due to the thermal cycling can lead to the forming of faulty SPF parts. In addition, thermo-mechanical fatigue and creep can cause cracking, which eventually lead to un-repairable damage to the tool. The aim of this paper is to investigate the thermo-mechanical distortion behaviour of a representative large SPF tool under realistic forming conditions using finite element analysis. Platen-tool contact and clamping pressure along the edges of the tool during the dwell time are modelled. The effects of heating and cooling cycles on tool distortion are analysed using different thermal histories with different heating and cooling rates. The effect of batch size on tool distortion is evaluated to optimise the batch size.

A. A. Deshpande

Papers

Combined Butt Joint Welding and Post Weld Heat Treatment Simulation Using SYSWELD and ABAQUS

Experimental and Numerical Characterization of the Cyclic Thermomechanical Behavior of a High Temperature Forming Tool Alloy

Finite element-based analysis of experimentally identified parametric envelopes for stable keyhole plasma arc welding of a titanium alloy:

Finite-element-based parametric study on welding-induced distortion of TIG-welded stainless steel 304 sheets:

Finite element based predictions of life limiting behaviour for a large SPF tool