Modeling of residual stresses by HY-100 weldments Page: 5 of 8
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RESULTS AND DISCUSSION
The residual stress distribution in a GTA spot welded HY-100 steel disk was analyzed
using thermo-mechanically uncoupled FE formulation. The computations used temperature-
dependent thermo-physical and mechanical properties of the base metal (BM). The thermal
analysis was based on the heat conduction formulation with the Gaussian heat input from the arc.
An axisymmetric FE model was developed which considerably simplifies the modeling effort.
One half of the actual disk cross section was meshed by linear four-noded finite elements.
Computations were performed by using a general purpose FE code.
Two computational steps are required to compute the residual stresses in welding. In the
first step, the heating/melting of the material is modeled by applying the heat flux. Cooling
transients are calculated in the second step when the heat source is removed and the disk is
cooled to room temperature. The heating time is five seconds, whereas the disk is cooled until
the isotherm ambient temperature is reached. Figure 3 shows temperature profiles at specific
distances from the weld centerline.
3000 N. am2500
2000
TI-C]
1500
1000
5000 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
time (s)
Figure 3. Temperature transient at depth of 1 mm.
Rate-independent, elasto-plastic constitutive equations were constructed from the uniaxial
tensile test results of the base metal under various temperature conditions. Both yield and
ultimate stresses were reduced to 5.0 MPa at the melting temperature to simulate low strength at
high temperatures. Elastic modulus and Poisson's ratio were also given as a function of
temperature. The elastic modulus was reduced to a small value (1.0 GPa) at high temperatures.
Phase transformation effects due to rapid cooling on mechanical properties of carbon steel were
not included at this stage of the analysis.
The same FE mesh as in the thermal analysis was used in the mechanical analysis, except
for the element type and different boundary conditions. The analysis is based on the temperature
gradients calculated in the thermal analysis which represent the input information or loading.
The disk was restrained in the axial direction on the bottom surface to appropriately model the
actual welding conditions.
Residual stresses and elastic strains were evaluated after the welding process was
completed and disk had cooled to room temperature. Comparison with the ND results was made
at this point and is shown in Fig. 4.3
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Zacharia, T.; Taljat, B. & Radhakrishnan, B. Modeling of residual stresses by HY-100 weldments, article, February 1, 1997; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc687927/m1/5/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.