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Material composition proportions and the thermal expansion coefficients of samples.
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Carbon composite is widely used in various fields, including the aerospace industry, electrical engineering, transportation engineering, etc. For electrified railways, the pantograph strip utilizes carbon composite as the current collector, which might bear multiple impacts from electrical, mechanical, or thermal aspects, from unwanted arcing, rain...
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Carbon-fiber-reinforced plastic is an important building material; however, its application is limited because of its brittleness, leading to vulnerability under shock. Thus, the strength performance of carbon-fiber-reinforced plastics needs to be improved. Here, the drop impact test was conducted to analyze the impact energy and fracture character...
Citations
... An effective method is to add appropriate stronger materials into pure copper to form a composite material, such as ceramic particles, fibers and graphene. Typically, graphene is an excellent strengthening materials due to its high fracture strength, electrical conductivity, ductility and Young's modulus [3][4][5]. ...
The mechanical performance of pure copper can be significantly strengthened by adding graphene without greatly sacrificing its electrical and thermal conductivity. However, it is difficult to observe the deformation behavior of Cu/graphene composites efficiently and optically using experiments due to the extremely small graphene size. Herein, Cu/graphene composites with different graphene positions and layers were built to investigate the effect of these factors on the mechanical performance of the composites and the deformation mechanisms using molecular dynamics simulations. The results showed that the maximum indentation force and hardness of the composites decreased significantly with an increase in the distance from graphene to the indentation surface. Graphene strengthened the mechanical properties of Cu/graphene composites by hindering the slip of dislocations. As the graphene layers increased, the strengthening effect became more pronounced. With more graphene layers, dislocations within the Cu matrix were required to overcome higher stress to be released towards the surface; thus, they had to store enough energy to allow more crystalline surfaces to slip, resulting in more dislocations being generated.
... On the other hand, it is a fact that there is no structure that combines all these properties. The thermal shock resistance and the critical number of thermal cycles of materials can be determined by correlating the thermal loading parameters with the weakening of the mechanical properties corresponding to the changes observed in the microstructure [24][25][26][27]. ...
Recently, high-temperature composites reinforced with in-situ phases have been developed as a new class of composites for harsh environments. The behaviour of these composites under sudden heating and cooling conditions is greatly influenced by the type and fraction of components. The aim of this study is to investigate the microstructural properties and mechanical response of iron based composites after thermal shock cycling. The fabrication process involved in-situ powder metallurgy (IPM) sintering of Fe–B4C starting powders. The samples were subjected to thermal shock with a constant temperature differences (ΔT: 600 °C) and varied cycles (N: 1–50). Comparison of microstructural changes and mechanical behaviour before and after thermal shock has been carried out. The boron atoms released from the initial B4C generated diffusion zones in the matrix dominated by iron boride phases (Fe2B/FeB). An effective matrix-reinforcement interface has been created by in-situ powder metallurgy, where boride phases are almost homogeneously distributed in the iron matrix. While the hardness of the composites was significantly developed by the Fe2B/FeB phases, the addition of B4C resulted in a reduction in the coefficient of thermal expansion (CTE). The in-situ phases contributed in the minimisation of the coefficient mismatch by balancing the thermal expansion coefficients between iron and the initial B4C. Under the influence of thermal shock, microcracks and then macrocracks formed on the sample surfaces, increasing in width and depth with thermal cycles. This resulted in accelerated fracture damage under post-thermal loading. Both the impact and flexural strengths of the samples were significantly reduced as the number of thermal cycles increased. Although the 20% B4C reinforced composite provided maximum hardness, it showed poor resistance to thermal loading. The best results for mechanical loads were achieved by the 5% B4C reinforced composite, which showed no cracks even after 50 thermal cycling.
... Pierson, H.O. [26] explained that pores within carbon blocks inhibited the movement of electrons, thereby resulting in increased electrical resistivity. Additionally, Wei, W. et al. [27] reported that electrons within carbon blocks moved along the solid regions, composed of fillers and binders, but their movement was disrupted when they collided with pores. The observations made in this study can also be interpreted similarly. ...
In this study, isotropic coke and coal tar pitch were subjected to compression molding while varying the compression pressure and holding time. As a result, carbon blocks were fabricated, and their mechanical properties and microstructure were analyzed, with respect to applied pressure and holding time. The compression pressure was set to 70, 100 and 130 MPa, while the holding time was set to 1, 2 and 3 min. Overall, with an increase in compression pressure, bulk density increased while porosity decreased. Increased compression pressure also led to enhanced mechanical and electrical properties. Microstructural analysis confirmed that, after compression molding granules that were larger than existing kneaded particles appeared. The formation of granules is attributed to the tendency of kneaded particles to connect and coalesce with each other under applied pressure during the compression molding process. As the compression pressure increased, the proportion of granules in the microstructure increased while the size of pores decreased. This phenomenon can be attributed to kneaded particles coming closer to each other under applied pressure. At a compression pressure of 130 MPa, both bulk density and porosity increased with a longer holding time. Some pores existed within granules, while others protruded out of granules, thereby forming long channels of connected pores around them. This microstructural change was considered to result in degraded mechanical and electrical properties.
... From here we will pass to discuss briefly on the protective shield containing pores as appear in [61] - [64] and their effect over the protective shield, which will be also examined in the current essay continually in Sec. 4 -5. Wei et al. [61] investigated how rapid temperature changes (thermal shock) damage carbon composite used in pantograph strips for electric trains. ...
... From here we will pass to discuss briefly on the protective shield containing pores as appear in [61] - [64] and their effect over the protective shield, which will be also examined in the current essay continually in Sec. 4 -5. Wei et al. [61] investigated how rapid temperature changes (thermal shock) damage carbon composite used in pantograph strips for electric trains. ...
... Graphite materials less durable against the thermal shock (tens of percent decrease in resistance) which is confirmed qualitatively by the literature [61]. Alternatively, visco-elastic modelling should be considered in future instead of enclosed elastic foam. ...
This study investigates a composite double-layer structure for improved thermal shock resistance. A modified Hugoniot elastic limit model is presented for the composite, followed by a 2D thermo-elastic impact simulation using commercial software. The simulation focuses on a composite material with alternating metallic (Steel, Aluminum) and non-metallic layers (Kevlar 49, Graphite). The objective is to optimize the composite's durability by strategically placing reinforcement particles within specific layers. The analysis explores the effect of different particle types (oil, water, Aluminum, Steel) and sizes (0.3mm, 0.5mm, 1mm) on the composite's stress response. It was found that aluminum and steel particles significantly reduce stress compared to fluid/gas particles, confirmed qualitatively by literature. Kevlar particles within the SiCp layer enhance its resistance, while Aluminum particles within the Kevlar layer offer weight reduction benefits. Moreover, for Kevlar, larger particles improve resistance, and vice versa for the SiCp case. Considering weight, a particle size of 0.5mm is chosen for both layers. Finally, a finite element analysis of the optimized composite model subjected to thermo-elastic impact loading demonstrates its superior performance compared to the non-reinforced composite. Specific layer combinations (SiCp with Kevlar particles, Graphite or Kevlar with Aluminum particles) show the most significant stress reduction.
... Based on the Rayleigh integral theory, Wei et al. [152] established a Rayleigh integral model of ultrasonic propagation in pantograph slide. The optimum range of the probe parameters was determined by studying the distribution law of the ultrasonic field inside the pantograph slide under different probe frequencies and diameters. ...
As the unique power entrance, the pantograph–catenary electrical contact system maintains the efficiency and reliability of power transmission for the high-speed train. Along with the fast development of high-speed railways all over the world, some commercialized lines are built for covering the remote places under harsh environment, especially in China; these environmental elements including wind, sand, rain, thunder, ice and snow need to be considered during the design of the pantograph–catenary system. The pantograph–catenary system includes the pantograph, the contact wire and the interface—pantograph slide. As the key component, this pantograph slide plays a critical role in reliable power transmission under dynamic condition. The fundamental material characteristics of the pantograph slide and contact wire such as electrical conductivity, impact resistance, wear resistance, etc., directly determine the sliding electrical contact performance of the pantograph–catenary system; meanwhile, different detection methods of the pantograph–catenary system are crucial for the reliability of service and maintenance. In addition, the challenges brought from extreme operational conditions are discussed, taking the Sichuan–Tibet Railway currently under construction as a special example with the high-altitude climate. The outlook for developing the ultra-high-speed train equipped with the novel pantograph–catenary system which can address the harsher operational environment is also involved. This paper has provided a comprehensive review of the high-speed railway pantograph–catenary systems, including its progress, challenges, outlooks in the history and future.
... Therefore, many research centers around the world are trying to explore and describe the phenomena occurring at the interface of these materials. For example, problems resulting from additional adverse phenomena associated with difficult operating conditions during operation are considered, such as rain, snow or ice and heat and the occurrence of an electric arc, thermal shock, abrasive, and catastrophic wear, etc. [1][2][3][4][5]. These difficult working conditions and the presence of high currents at the point of contact cause material degradation, which affects the quality of cooperation of this friction pair [5][6][7][8]. ...
This article presents the methodology, description, and results of experimental studies aimed at determining the impact of the copper concentration in a carbon–metal composite contact strip on the maximum temperature of the copper contact wire during a contact event when used for operation in the railway industry in Europe. Based on these tests, we determined the minimum percentage of copper that is required for the composite to meet the normative requirements for current loads. In addition to experimental research, a 3D FEM numerical model was also developed in which the contact strip and contact wire geometry were mapped, along with imposed loads resulting from the test for current loads mentioned above. Fifteen simulation variants were carried out for the established model, where the value of the thermal conductivity coefficient and the specific heat coefficient were varied. On this basis, we analyzed the sensitivity of thermal coefficients to the contact wire temperature and determined the minimum conductivity coefficient value, which allowed the maximum copper contact wire temperature of 120 °C to be obtained during the verification tests.
... When carbon strip is in service, its maximum temperature generally rises to 400°C or so [22]. So, the maximum temperature of thermal shock was design at 500°C. ...
Carbon material, because of its high thermal conductivity, ablation resistance and friction resistance, has been widely used in the field of electrical engineering. When confronted strong thermal shock, the interface structure of carbon material would cause thermal shock damage by the rapid temperature difference. In order to systematically and quantificationally study the thermal shock damage of carbon materials, an experimental system that can provide rapid temperature difference was built. The experimental results showed that undergoing a temperature difference of 485 °C, more micro-cracks and holes arose in the pure carbon material, resulting in an increase of porosity by 26.39%, an increase friction coefficient by 48.65%, and a decrease of compressive strength by 23.96%. It was also found the ultrasonic velocity linearly decreased with the increase of porosity and the decrease of the compressive strength caused by thermal shock, which meant the non-destructive ultrasonic testing can be used to conveniently and accurately quantify the thermal shock damage. This conclusion also applies when testing copper-impregnated carbon material, making it a potential method to be used in the maintenance of pantograph which can effectively avoid in rail transit accidents.
Graphical abstract
... Frictional heating, Joule heating and arc discharge were favorable for oxidation reaction of copper. 32) In addition, the current would induce electrochemical oxidation on Cu surface, which could further aggravate the surface oxidation. 19,33) The O:Cu atomic ratio on worn surface based on EDS was shown in Fig. 10. ...
The tribological and conductive performance of the rolling current-carrying pairs were studied at different rotation speeds based on the disc-disc Cu pairs. Whether the current was applied or not, the friction coefficient decreased with the increasing of rotation speed. The average contact resistance increased with the rotation speed and the applied current. The sharp fluctuation of the real-time current was proposed as the failure criterion for the rolling current-carrying pairs, and both the rotation speed and the current accelerated the failure process. Erosion pits and melting could be observed by SEM, and the surface oxidation could be detected by EDS on the failure surface. It was speculated that arc discharge appeared under high speed and large current conditions, which encouraged the transformation of damage mechanism from mechanical wear to arc erosion. These results may provide some useful suggestions on the failure mechanism and life tests of the electro-conductive rotary joints.
Fig. 2 Sketch map of the rolling pairs. (a) Disc-disc contact; (b) Schematic diagram of the appearance; (c) Schematic diagram of the rolling contact and electrical circuit system. Fullsize Image
