# Assessment of Uneven Wear of Freight Wagon Brake Pads
## 1 Introduction
Methods of microhardness, X-ray energy dispersion analysis, microscopic analysis and finite element computational methods are used for the analysis. The results show that magnetic composite pads have the highest strength and wear resistance due to reinforcing fillers such as calcium carbonate and wollastonite. At the same time, non-magnetic composite and cast-iron pads are inferior in microhardness and wear resistance. It should be noted that there is a need for further research into uneven wear and the distribution of forces in brake pads because those affect the efficiency. Scientific studies into the use of composite brake pads in rolling stock are related to traffic safety and environmental impact. Optimization of operating costs in the railway industry often leads to the situations where brake pads are considered as a product purchased at the lowest possible price, provided that they have satisfactory performance. However, this approach may not minimize long-term costs. The material for friction elements directly impacts the durability of wheel pairs; the cost of their replacement significantly exceeds the cost of replacement of other components of the wagon, as indicated in [9]. This highlights the need for an innovative approach to the selection of brake pad materials, thus assessing the overall operating costs and the lifespan of major rolling stock elements. Reference [10] deals with the interaction of EU railway systems, in particular, the assessment of the brake characteristics of wagons manufactured both in Western European and post-Soviet countries. The main purpose of the research is to study the methods for calculating the braking mass and the pressure force from the brake pad to the wheel, as well as to assess the possibilities of implementing these methods within the EU single transportation system. Emphasis is placed on analyzing the compatibility of existing standards based on different approaches for assessing the braking characteristics of freight and passenger rolling stock. A disadvantage that significantly complicates the unification process is the uneven distribution of brake forces on the pad of bogies, which can lead to calculation errors. The brake systems in road transportation are one of the key issues in ensuring road safety. Reference [11] focuses on the importance of the brake pad design, in particular, on the materials from which brake pads are made, and their interaction with other elements of the system. It is also emphasized that the wear of brake pads is accompanied by the occurrence of noise, which negatively affects human health. The study presents the analysis of how the pad design impacts the formation of noise; the authors also describe measures for its reduction. In particular, one of them is the use of insulators in the pad design and materials that reduce noise in the human environment. However, the study does not cover such an important problem as the uneven wear of pads, which is characteristic of both road and railway transport, for the correction of which the wedge dual ratio can be used. Study [12] shows that the pressing force of brake pads largely depends on the dynamic processes in the lever transmission. As a result, the distribution of the pressing force between the pads may be uneven, which directly affects the wear intensity. Thus, there is an urgent need for developing new methods that take into account such factors and contribute to improving the operational efficiency of railway cars. Study [13] proposes a regression model of the friction between pads and wheels of industrial transport locomotives, taking into account structural uncertainty and a significant number of input variables, including the friction coefficient. The author has successfully eliminated unstable solutions in the multiparameter model based on his own approach to solving the problem. However, when identifying models, a key parameter, i.e., wear in thickness, was not taken into account, which is critical when scheduling repairs and using certain brake pads for safety reasons.