Model of Crack Initiation in a Brake Drum
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l of Crack Initiation in a Brake Drum S. A. Askerov* Azerbaijan Technical University, Baku, AZ1073 Azerbaijan *e-mail: [email protected] Received January 27, 2020; revised July 5, 2020; accepted July 7, 2020
Abstract—In this paper, we perform a theoretical analysis to determine the quantitative relationship between abrasive wear and crack initiation in a brake drum when a wheeled vehicle is braking. Using the model of a rough friction surface, a closed system of algebraic equations that allows one to study cracking in the brake drum depending on the abrasive wear of the friction surface is constructed. The developed model is shown to allow calculating the effect of wear on crack initiation in the brake drum in the design stage. Keywords: brake drum, friction surface roughness, crack initiation, wear DOI: 10.3103/S1068366620050049
INTRODUCTION With the growth of the car market and increase in travel velocities, the requirements for efficient and reliable braking systems of wheeled vehicles are constantly becoming more rigorous. Increased vehicle production and increased traffic require improved braking mechanisms. Therefore, research aimed at improving the efficiency of braking mechanisms and, first of all, improving car brakes are of great importance for the industry. Studies on heating, wear, and stress-strain state were carried out for disc and drum brakes [1–3]. The main directions of increasing the reliability and efficiency of brake mechanisms are constructive and technological methods for improving tribo-couplings, rational selection of friction materials, and the creation and application of new calculation methods that allow controlling the material destruction process during contact interaction. Besides, the development and testing of braking mechanisms and friction materials are also included [4–6]. At the current stage of development of material strength, considerable attention is paid to the concepts of fracture mechanics of materials. In this case, the process of fracture, i.e., strength loss, is interpreted as the process of initiation and development of a crack in a material. To ensure the safety of vehicles, it is important to develop a calculation model during the design stage that allows prediction of cracking in the drum of the brake mechanism depending on the level of its wear [7, 8]. This study is aimed at developing a mathematical model of the “drum–pad” pair that allows calculating the wear of the friction surface and its effect on crack initiation in the drum.
PROBLEM FORMULATION Let us consider the stress-strain state of the drum when braking a wheeled vehicle. In the intermittent braking mode, interaction between the contacting surfaces of the drum and the pad occurs and friction forces leading to wear of interface materials arise. In this case, the brake drum of a wheeled vehicle is subjected to cyclic loading. In this case, stress concentrators (areas of weakened interparticle bonds of the material) are believed to be appear in the drum material. For definiteness, let the load be change
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