Rolling contact fatigue of railways wheels: Influence of steel grade and sliding conditions

AbstractThe aim of this work is to develop a numerical approach which is able to compare the different steel grades influence on rolling contact fatigue of railways wheels according to practical conditions. The main stages are the identification of the material behavior, the determination of the stress-strain fields and the application of a fatigue criterion. Two steels usually used for the manufacturing of wheels have been studied, R9T and 50CrMo4. Their influence has been numerically studied. Results show that the threshold of elastic and plastic shakedown differs depending on the steel grades and consequently the risk of damage can be affected. This methodology allows a classification of the material grades face the risk on rolling contact fatigue

Plasma density profile reconstruction of a gas cell for Ionization Induced Laser Wakefield Acceleration

Laser-driven plasma wakefields can provide hundreds of MeV electron beam in mm-range distances potentially shrinking the dimension of the actual particle accelerators. The plasma density plays a fundamental role in the control and stability of the acceleration process, which is a key development for the future electron injector proposed by EuPRAXIA. A gas cell was designed by LPGP and LIDYL teams, with variable length and backing pressure, to confine the gas and tailor the gas density profile before the arrival of the laser. This cell was used during an experimental campaign with the multi TW-class laser at the Lund Laser Centre. Ionization assisted injection in a tailored density profile is used to tune the electron beam properties. During the experiment, we filled the gas cell with hydrogen mixed with different concentration of nitrogen. We also varied the backing pressure of the gas and the geometrical length of the gas cell. We used a transverse probe to acquire shadowgraphic images of the plasma and to measure the plasma electron density. Methods and results of the analysis with comparisons between shadowgraphic and interferometric images will be discussed