Three dimensional transient finite element model for residual stress and solidification in the GMAW Process for AISI 304 stainless steel

Networking three fields of welding--thermal, microstructure, and stress--was attempted and produced a reliable model using a numerical method with the finite element analysis technique. Model prediction was compared with experimental data in order to validate the model. The effects of welding process parameters on these welding fields were analyzed and reported. The effort to correlate the residual stress and solidification was initiated, with some valuable results. The solidification process was simulated using the formulation based on the Hunt-Trivedi model. Based on the temperature history, solidification speed and primary dendrite arm spacing were predicted at the given nodes of interest. Results show that the variation during solidification is usually within an order of magnitude. The temperature gradient was generally in the range of 10$\sp4-10\sp5$ $\sp\circ$K/m for the given welding conditions (welding power = 6 kW and welding speed = 8, 12, 18 ipm), while solidification speed appeared to slow down from an order of 10$\sp{-1}$ to 10$\sp{-2}$ m/sec during solidification. For the primary dendrite arm spacing (PDAS), the values were in the range of 10$\sp1-10\sp2\ \mu$m. The range of the sizes was in agreement with the experimental values. SEM images were also taken. It was observed that the average size of PDAS was dependent upon the welding speed. They were measured between about 7.5 to 20 $\mu$m for columnar and 10 to 30 $\mu$m for equiaxed for welding speeds between 8 to 18 ipm (3.336 to 7.62 mm/sec). When the welding speed increased, it was observed that the average size of PDAS decreased as the model predicted. For grain growth at HAZ, Ashby's model was employed. The prediction was in agreement with experimental results. For the residual stress calculation, the same mesh generation used in the heat transfer analysis is applied to make the simulation consistent. The analysis consists of a transient heat analysis followed by a thermal stress analysis. An experimentally measured strain history was compared with the simulated result. The relationship between a microstructure and the stress/strain field of welding was also obtained.U of I OnlyETDs are only available to UIUC Users without author permissio