Numerical Simulation of Induction Hardening of Torsion Bar
In order to improve the fatigue performance of torsion bar, induction surface hardening is performed. The aim of the present study is to compare the experimental residual stress fields measured by X-ray diffraction with those predicted from finite element modeling of the whole induction surface hardening process. Temperature and residual stress distributions are affected by the component geometry, the material behavior and the induction treatment parameters. Based on the residual stress distribution and the fatigue loading, cracks can nucleate from the surface or below the hardened layer. Therefore, it is very important to determine the residual stress distribution and optimize the process, especially for safety critical engineering components. Results of present study show that the improvement of fatigue performance is due to development of both hard microstructure and compressive residual stress at the surface layer of torsion bar during induction hardening.
Model for the solid state phase transformation and transformation plasticity during casting in grey cast iron GJL350
The development of stresses and distortions in solidifying metallic components during casting processes is not only influenced by the temperature field created across the mould but can also be strongly influenced by the transformation kinetics occurring in the solidifying metal. It is challenging to apply numerical methods which are strictly based on a coupled thermo-mechanical model because the models do not account for the inhomogeneous distribution of alloying elements, particularly carbon. Therefore a viable model has to take into account some preselected difference by heated states using short-time austenitizing, which includes a carbon gradient in order to understand the influence of carbon on thermomechanical properties. The aim of the present work is to identify high temperature parameters for a lamellar cast iron GJL-350 in order to include them into a material model. The transformation kinetics for non-isothermal transformations are determined from measured isothermal TTT-diagrams at differently heated states. Doing so, it was also possible to determine the isothermal TTT-diagrams as a function of the carbon content in the matrix.
A Study on the Distribution of Residual Stress Due to Surface Induction Hardening
A finite element method (FEM) is used here to analyse the distribution of residual stresses generated by surface induction hardening. The analysis considers both transformation induced plasticity (TRIP) and latent heat effects. The calculation model considering TRIP is found to improve the agreement with experimental measurements significantly. From a large number of numerical results, a set of simple formulas is derived to predict the residual stress distribution in the workpiece.