Marcin Kubiak

Theoretical investigations into heat transfer in laser-welded steel sheets

This study contains mathematical modelling and numerical analysis of heat transfer in laser beam welding process. The temperature field was obtained on the basis of numerical solution into unsteady heat transfer equation with convective term and volumetric heat sources taken into account. Volumetric heat source model describing laser beam power distribution in combined truncated cone–cylinder volume was developed. Due to the wide range of temperatures appearing in the process latent heat of fusion, evaporation as well as latent heat of phase transformations in solid state were taken into account in the solution algorithm. On the basis of developed numerical algorithms an analysis of heat transfer in laser butt-welded steel sheets as a three-dimensional initial-boundary problem was performed.

Numerical estimation of phase transformations in solid state during Yb:YAG laser heating of steel sheets

This work concerns the numerical modeling of heat transfer and phase transformations in solid state occurring during the Yb:YAG laser beam heating process. The temperature field is obtained by the numerical solution into transient heat transfer equation with convective term. The laser beam heat source model is developed using the Kriging interpolation method with experimental measurements of Yb:YAG laser beam profile taken into account. Phase transformations are calculated on the basis of Johnson - Mehl - Avrami (JMA) and Koistinen - Marburger (KM) kinetics models as well as continuous heating transformation (CHT) and continuous cooling transformation (CCT) diagrams for S355 steel. On the basis of developed numerical algorithms 3D computer simulations are performed in order to predict temperature history and phase transformations in Yb:YAG laser heating process.

Simulations and numerical model of steel hardening process

This paper describes modelling of the processes of steel C80U hardening. The first priority was given to thermal phenomena, phase transformations in solid state and mechanical phenomena. The issue of heat conductivity was based on the equation of transient heat conductivity with unit source. Numerical algorithms for kinetics of phase transformations and evaluation of fractions of phases were built on the diagrams of continuous heating and cooling of tool steel. The theoretical model of phase transformations was then verified by experiments. In modelling of mechanical phenomena, the equilibrium equations and constitutive relations were adopted in the rate form. Plastic strains are determined by the theory of non-isothermal plastic flow associated with the Huber-Misses condition. The model assumed isotropic and kinematics strengthening and besides elastic, thermal, structural, plastic strains and transformations plasticity were included. Thermophysical properties including the Young’s modulus, tangent modul...