Flow stress determination

A new method has been established by which the temperature and microstructural dependency of the flow stress in welding stress simulation tools such as WeldsimS can be relatively easily determined. The method is based on Satoh testing and on using an ideal plasticity law for the flow stress. It requires prior knowledge to the relevant CCT diagram.

  • Although Satoh test samples are thermally inhomogeneous, and thus also the phase transformations and associated density changes as well as the occurrence of transformation plasticity, it has been shown how the Satoh test can be applied for extracting flow stress values at the different temperatures. The method relies on prior quantification of the relevant CCT diagram, and the results are limited to the temperature intervals in which phase transformations do not occur.
  • It is assumed that the Satoh stress-temperature curves reflect all relevant phenomena such as work hardening, strain rate sensitivity, and the flow stress dependency on the specific mixture of phases appearing at the different temperatures. All these phenomena are then accounted for by fitting the temperature dependent yield stress of an elastic – ideal plastic material law to the stresses measured in the Satoh test.
  • The Satoh test sample is subjected to constrain and a temperature cycle similar to that taking place in the HAZ during welding. By means of modelling, it has been shown that the stress development during the Satoh test temperature cycle can be considered, with sufficient degree of accuracy, as representative for that taking place in all material points of the HAZ during the real welding operation.

Satoh test results for the X70 samples have been established along with the establishment of the approximate constitutive model for this steel type and applied in a case study (see Figure below).

The Satoh test.


Residual stress simulation based on the simplified method (blue curve) compared to simulation based on a constitutive model accounting for work hardening (green curve). The curves at the left figure are along the black surface line at the right figure, which shows one of two symmetric welded plates. The Satoh "test results" from which data for the simplified model are extracted are simulated using the work hardening model.

Published January 5, 2007