Seznam abstraktů 2025: POSTEROVÁ SEKCE B

Strengthening the railway network is a key measure in tackling climate change, as it enables low-emission mobility and helps reduce road traffic. Maintenance plays a crucial role in this, with aluminothermic welding commonly used for rail repairs.

This project aims to develop an in-house tool for microstructure modeling under continuous cooling conditions, enabling predictions of phase composition and hardness in aluminothermically welded rails.

The numerical model is based on the Finite Difference Method (FDM) and describes the temporal and spatial evolution of temperature and microstructural phases. The microstructure evolution is modeled using an adapted Kirkaldy equation, which also takes into account the latent heat released during phase transformations. An end-quench specimen is used as a reference body.

The model has been validated against a reference case from the literature investigating the thermal and microstructural behaviour of C45 steel. The predicted temperature profiles show reasonable agreement with published data. At low cooling rates, the model successfully captures phase transformations with phase fractions in good agreement with experimental results. At higher cooling rates some deviations are observed, particularly in the prediction of bainite and martensite.

As a next step, additional in-house experiments on C45 steel are planned to obtain a broader statistical data set.
This will help to improve our understanding of the variability in phase transformation and further improve the accuracy and reliability of the model.
The developed model is expected to contribute to a better understanding of microstructure evolution in aluminothermic welding processes. This knowledge will support future improvements in process robustness and efficiency, ultimately strengthening the reliability of rail infrastructure.

In metal forming process, lubricant film plays an important role in determining tool life and acts as an essential factor in the productivity. In many lubrication problems, the flow of fluids independent of the pressure, surface structures, capillary invasion, and thermal conductivity variation is described in detail by the famous Reynolds equations. Intrinsically unsteady aspects of metal forming processes in general, both forging and stretching forming, lead to transient tribological effects. In most metal forming operations, the lubricant could not undergo an isothermal environment due to the deformation heat of workpiece and viscous heating in lubricant flow, which is induced partly by the relative motion between tool and workpiece. High pressures in metal forming processes lead to a significant shear stress by the relative motion between contact surfaces. Heat is generated in the lubricant by the shear stress along with the sliding-induced shear rate. The main objective of this study is to establish a lubrication model in order to predict lubricant film thicknesses between tool and workpiece interfaces and study the effect of film thicknesses in cold forming operations.

In the present study, Hydrodynamic lubrication theory was applied to calculate entrapped fluid lubricant film thicknesses. A commercially available Rigid Plastic FE code Deform 2-D has been employed to simulate deformation of thin billets and necessary data have been extracted and transferred into lubrication models in order to estimate local film thicknesses. Aluminum AA1100 have been employed as model materials and castor oil as lubricant model. Numerical models for lubrication films were constructed based on Reynolds equation for lubrication and discretized by Finite Differences Method (FDM) in analysis.

Extensive simulation studies in upsetting of solid cylindrical billets have been carried out in order to analyze deformation of workpiece and to investigate lubrication film thicknesses, film formation and transportation. Entrapped film thicknesses were compared with the results given by previous researches to illustrate the validity of simulation models. Results were presented in terms of film thicknesses, contact pressure, sliding velocities, volume of entrapped lubricant, lubricated regions, tool wear and discussed its variation with process parameters.

This study presents the experimental investigation of Heat Transfer Coefficient (HTC) distributions conducted within the framework of the European RFCS SmartCool project. The SmartCool project focuses on the development and implementation of a smart-controlled actuator system designed to homogenize the temperature distribution across the width of the transfer bar in hot strip mills. The primary objective is to enhance product flatness and mechanical properties by minimizing temperature gradients, particularly in advanced high-strength steel (AHSS) production.
A series of laboratory-scale measurements were performed using a custom-designed test bench equipped with a moving stainless-steel test plate and embedded thermocouples. The plate was subjected to intensive cooling by a segmented header equipped with solid jet nozzles, divided into seven zones. The cooling process occurred in a narrow gap, allowing for close-range, high-intensity water application. Measurements focused on quantifying the differential cooling capabilities and assessing the impact of water flow rate distribution across the nozzle sections.
The results confirmed that the cooling intensity is naturally determined by whether the corresponding cooling zone is active. However, it was also observed that the influence of neighboring active zones is extremely strong—significantly altering the cooling intensity in the measured area. The presence or absence of cooling in adjacent zones considerably impacted the achieved HTC values, with isolated zones showing reduced cooling efficiency.
The findings provide useful insights for optimizing the setup and control of intensive cooling systems, contributing to a better understanding of how cooling strategies affect thermal profiles in industrial processes.