Deformations and Stresses in Welded Panels: Development and analysis of a simulation procedure for two-pass fillet welding of a stiffener to a plate
Typ
Projektarbete, avancerad nivå
Program
Publicerad
2021
Författare
Boominathan, Thangam
Pujari, Aditya
Sjödin, Wilhelm
Stoyanova, Monika
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
This project is a part of the Masters programme Applied Mechanics at Chalmers and will also be a contribution to a benchmark exercise in a Specialist Committee, V.3 Material and Fabrication Technology for the International Ship and Offshore Structures Congress (ISSC) 2022 Conference. The goal of this project is to further develop and analyse an existing simulation procedure for two-pass fillet welding of a stiffener to a plate with the aim to find what simplifications that can be made in the modelling. The results from finite element simulations (FE-simulations) are then compared to analytical solutions and experimental data for validation.
The FE-simulations are carried out with the commercial FEA-software ABAQUS using forward-coupled thermal-mechanical FE-simulations with geometrical and material nonlinearities included. The analysis is first performed on a shorter plate (200 mm) to draw faster conclusions by saving computational time. Once the analysis for the shorter plate has been conducted, a longer plate (1000 mm) representing the benchmark geometry is analysed.
To verify that a simplified model of the heat input can be used, FE-simulations on the short plate are used to calculate the cooling time between 800˚C and 500˚C at a node on the weld. This data is then used to compare with analytical solutions for the cooling time in this interval, valid for the weld parameters specific to this benchmark project. By adapting the weld speed and maximum temperature of the weld, the optimal cooling time, and parameters for the heat input, are found. The simplified heat source model then gives the same behaviour as a real weld.
With the thermal simulation settings validated by analytical solutions, the results from the mechanical part of the FE-simulations are analysed for the short plate. Here different sequences of releasing mechanical boundary conditions are studied, and how they affect the residual deformations after the two-pass fillet welding. This is achieved in ABAQUS by changing simulation steps and compiling the deformation fields for different configurations. Furthermore, different methods for preventing rigid body motion (RBM) are analysed and their influence on the residual deformations. Mechanical contact between a table beneath the plate is modelled using Lagrange multipliers creating a hard contact. The effect of this contact modelling on the residual deformations is also investigated, whether it is necessary or not since a removal of contact conditions will reduce computational cost considerably. One conclusion that can be drawn is that the release of mechanical boundary conditions is mainly elastic, and thus they can be modelled as removed at the same time. Furthermore, it is seen that the mechanical contact modelling is necessary to obtain reasonable results for some methods of preventing RBM.
The long plate is then studied, where the complete benchmark geometry is modelled. Using Chalmers Centre for Computation Science and Engineering (C3SE) one complete simulation is run in a reasonable time of 12 hours on 24 CPUs. The residual stresses and deformations are then extracted and compared to experimental data on angular distortion and deformations. It is found that the simplified modelling approach used can give good agreement for the residual stresses and for the shape of the residual deformations. The magnitudes of the residual deformations, though, are harder to predict.