K. Aniołek

Numerical Modeling of Load and Stress on the Contact Surface of a Turnout and a Railway Vehicle

AbstractIn operating conditions, railroads are subject to abrasive and fatigue wear. Their durability period depends on the properties of the materials from which rail sections are made, the characteristics and value of the load, and the distribution of contact stresses and strain in the places at which wheels contact track and turnout components. Forecasting of the real load and the resultant contact stress and strain makes it possible to rationally design railway turnouts and correctly select the material to be used for their components. For these reasons, characteristics of load and, subsequently, distributions of contact stresses and deformations in places of wheel/turnout-component contact were determined in numerical calculations using Universal Mechanism and MSC.MARC computer applications. It was determined that the distributions of contact and reduced stresses depend on the load value. The highest reduced stresses occur in the contact zone and right under the rolling surface of the section.

Methodology and verification of calculations for contact stresses in a wheel–rail system

The distribution of contact stresses in the wheel–rail system is a decisive factor for the wear of elements and the safety of rail transport. Analytical calculations of stresses based on the Hertz theory can only be applied to elastic deformation of materials. High dynamic loads leading to plastic deformation (not considered in the Hertz theory) are a predominant cause of problems in the contact vicinity. These problems can be successfully resolved by applying the finite-elements method. Two- and three-dimensional test models were generated to estimate an error in numerical calculations in the MSC.MARC program. We compared the results of numerical calculations with analytical calculations. Based on the obtained results we defined the effect of parameters describing the finite-elements mesh on the calculation error for contact stresses, and adjusted mesh parameters appropriately to achieve as low as possible error in numerical calculations. We also defined the effect of material characteristics on the value of contact stresses on the wheel–rail interface.

Characteristics of the tribological properties of oxide layers obtained via thermal oxidation on titanium Grade 2

Thermal oxidation is an effective technique for modifying the surface of titanium and its alloys in order to improve their poor tribological properties. This paper presents the results of tests concerning titanium Grade 2 subjected to thermal oxidation at 600 ℃ and 700 ℃ for 72 h. The morphology of the surface of the formed oxide scale was determined. The surface of a specimen oxidised at 600 ℃ was unevenly covered by very fine oxide particles. Raising the temperature to 700 ℃ made it possible to cover the entire examined surface with an oxide layer. The obtained scale was characterised by the presence of large irregularly shaped agglomerated oxide particles. Tribological tests showed that the presence of an oxide layer on the surface of titanium significantly improved the resistance of the interacting tribological couple to sliding wear. The obtained 3D isometric images of the trace of wear showed that the formed traces differed in terms of width, depth and shape. It was shown that the area of the cross section of the trace of wear decreased as the temperature of thermal oxidation increased. Scanning electron microscopic observations of traces of wear formed following tribological interaction with an Al2O3 ball showed, in a non-oxidised specimen and a specimen oxidised at 600 ℃, the presence of alternating morphologically varied areas formed as a result of corrugation wear. The oxide layer obtained at 700 ℃ has the highest resistance to sliding wear and completely eliminates the adverse corrugation wear phenomenon.