The research describes a micro-macro computer model that captures most of the physics of a weld pool, the fusion zone and the heat-affected zone in a low-alloy steel weld.
The macro-model uses either FEM or Smoothed Particle Hydrodynamic (SPH) methodology for the weld pool geometry.
The SPH model solves the transient 3D non-linear energy equation
for temperature and fraction solid and the Navier-Stokes equations
for velocity and pressure. This predicts
the transient weld pool size, shape and oscillations including transient temperature,
fraction solid, velocity, composition
including mixing and dilution and macro-scale solidification.
The number of particles ranges
from 50K to 500K with particle spacings of roughly 0.2 mm. Time steps are usually 0.2 microsecond and the number
of time steps is about 1 to 2M for 1 s physical time.
A micro-model for the evolution of microstructure in the FZ includes a model for dendrite growth during the weld pool solidification of a Fe-C-Mn alloy system. A 3D cellular approach is used for the dendrite growth simulation in the micro scale where the solid phase growth is controlled by the constitutional and capillary
at the liquid-solid interface.
This micro model is coupled to a macro-model of the weld in a welded structure.
Another micro-model describes the dissolution of ferrite and homogenization of austenite in a low-alloy steel weld.
A synthetic microstructure is introduced containing a representation of individual grains.
The process is driven by the thermal cycle and carbon diffusion.
Holistic frameworks are finally introduced for the HAZ and fusion zone
to establish correlations between the weld process parameters in the macro model
such as weld process type, weld
current, voltage, weld heat input, weld speed, base metal and filler metal composition
and the solidification microstructure as well as the solid state microstructure transformations
and mechanical properties in the neighborhood of a spatial point in macro-model.