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 New Vacuum Pressure Infiltration CFRP Method and Preparation Experimental Study of Composite
In order to prepare a carbon-fiber-reinforced polymer composite (CFRP) with ideal microstructure and properties, a new vacuum pressure infiltration CFRP method is proposed based on an analysis of existing CFRP preparation process methods. Research on composite material preparation systems was carried out by using this new method principle. The system mainly includes a fiber pre-forming module, a vacuum heating infiltration module, a hot-press curing molding module, and a data acquisition control module. Under the conditions of natural curing at 0 MPa + 6 h + 25 °C, vacuum heating curing at –0.05 MPa + 30 min + 80 °C, and hot-press curing at 0.7 MPa + 5 min + 50 °C, a two-dimensional (2D) CFRP with excellent microstructure and properties was successfully prepared. Observing the microstructure of the prepared composite material, it can be found that the inside of the composite material was sufficiently and uniformly infiltrated, and common preparation defects such as holes and delamination were effectively controlled. Through the performance test, the bending strength of the material reached 790 MPa.