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To ensure the operational safety of the automatic couplers of a rolling stock subjected to cyclic loading, reliability and residual service life must be determined. This paper involved the prediction of the durability of the automatic coupler SA3 by analytical summation of cyclic damage. During the investigation, the cyclic characteristics and damage modes of the automatic coupler material that influence the accumulation of damage are determined. The stress and strain state assessment model was developed using a 3D finite element method for the automatic coupler housing as a geometrically complex component. A methodology was used to assess damage per load cycle that is applicable to any sequence of automatic coupler load cycles. For this purpose, the authors used low-cycle stationary load dependencies that account for quasi-static and low-cycle fatigue damage. The investigation showed that a coupler may develop a crack due to accumulated quasi-static and fatigue damage. For damage summation, the dependences of low-cycle stationary stress-controlled load accounting for low-cycle, quasi-static fatigue damage are proposed in view of the variation of the load on the automatic coupler during operation depending on the weight of the rolling stock, velocity, and railway relief. The proposed methodology is applicable to the calculation of other housings under similar loading conditions.
To ensure the operational safety of the automatic couplers of a rolling stock subjected to cyclic loading, reliability and residual service life must be determined. This paper involved the prediction of the durability of the automatic coupler SA3 by analytical summation of cyclic damage. During the investigation, the cyclic characteristics and damage modes of the automatic coupler material that influence the accumulation of damage are determined. The stress and strain state assessment model was developed using a 3D finite element method for the automatic coupler housing as a geometrically complex component. A methodology was used to assess damage per load cycle that is applicable to any sequence of automatic coupler load cycles. For this purpose, the authors used low-cycle stationary load dependencies that account for quasi-static and low-cycle fatigue damage. The investigation showed that a coupler may develop a crack due to accumulated quasi-static and fatigue damage. For damage summation, the dependences of low-cycle stationary stress-controlled load accounting for low-cycle, quasi-static fatigue damage are proposed in view of the variation of the load on the automatic coupler during operation depending on the weight of the rolling stock, velocity, and railway relief. The proposed methodology is applicable to the calculation of other housings under similar loading conditions.
ZG25MnCrNiMo steel samples were prepared by squeeze casting under pressure ranging from 0 to 150 MPa. The effects of pressure on the microstructure, low-temperature toughness, hardness, and impact wear performance of the prepared steels were experimentally investigated. The experimental results indicated that the samples fabricated under pressure exhibited finer grains and a significant ferrite content compared to those produced without pressure. Furthermore, the secondary dendrite arm spacing of the sample produced at 150 MPa decreased by 45.3%, and the ferrite content increased by 39.1% in comparison to the unpressurized sample. The low-temperature impact toughness of the steel at −40 °C initially increased and then decreased as the pressure varied from 0 MPa to 150 MPa. And the toughness achieved an optimal value at a pressure of 30 MPa, which was 65.4% greater than that of gravity casting (0 MPa), while the hardness decreased by only 6.17%. With a further increase in pressure, the impact work decreased linearly while the hardness increased slightly. Impact fracture analysis revealed that the fracture of the steel produced without pressure exhibited a quasi-cleavage morphology. The samples prepared by squeeze casting under 30 MPa still exhibited a large number of fine dimples even at −40 °C, indicative of ductile fracture. In addition, the impact wear performance of the steels displayed a trend of initially decreasing and subsequently increasing across the pressure range of 0–150 MPa. The wear resistance of samples prepared without pressure and at 30 MPa was superior to that at 60 MPa, and the wear resistance deteriorated when the pressure increased to 60 MPa, after which it exhibited an upward trend as the pressure continued to rise. The wear mechanisms of the samples predominantly consisted of impact wear, adhesive wear, and minimal abrasive wear, along with notable occurrences of plastic removal, furrows, and spalling.
Draw hook failures present significant problems for railway safety and operational efficiency. Although failures on the draw gear are not frequent, they can induce serious problems on the vehicles and infrastructure when some elements break. This paper presents comprehensive research on the potential causes of these failures, aiming to provide insights for prevention measures related to materials, production process, geometry and manipulation practices during train operation. The draw hook, as one of the vital components in connections of wagons and locomotives, ensures the safety and reliability of trains during operation. By analyzing the historical failure data and relevant literature, this study identifies several key factors contributing to coupler failures. Material degradation emerges as a prominent concern, with factors such as fatigue, wear, and corrosion compromising the structural integrity of the coupler hook and other components over time. Overloading during starting, impacts, or improper coupling procedures further increase the risk of failures. Mechanical and physical characteristics of used material, as well as geometric inconsistencies, may also induce failure under operational conditions. Environmental factors, such as extreme temperatures, moisture ingress, and chemical exposure, pose additional challenges by accelerating material degradation and corrosion processes. Understanding the complex interaction of these factors is crucial for developing effective preventive maintenance strategies and for addressing and improving observed imperfections in draw gear elements. Implementing the results from this research can help railway operators and manufacturers of subjected elements mitigate the risk of failures, thereby ensuring the continued reliability and safety of rail transportation systems.
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