Carbon nanotube (CNT) and graphene-reinforced nanocomposites have become exceptional multifunctional materials because of their exceptional mechanical, thermal, and electrical properties. Recent developments in synthesis methods, dispersion strategies, and interfacial engineering have effectively overcome agglomeration-related limitations by significantly improving filler distribution, matrix compatibility, and load-transfer efficiency. These nanocomposites have better wear durability, corrosion resistance, and surface properties like super-hydrophobicity. A comparative analysis of polymer, metal, and ceramic matrices finds benefits for applications in biomedical, construction, energy, defense, and aeronautics. Functionally graded architecture, energy-harvesting nanogenerators, and additive manufacturing are some of the new fabrication processes that enhance design flexibility and functional integration. In recent years, scalability, life-cycle evaluation, and environmentally friendly processing have all gained increased attention. The development of next-generation, high-performance graphene and carbon nanotube (CNT)-based nanocomposites is critically reviewed in this work, along with significant obstacles and potential next steps.

Friction Stir Processing (FSP) has emerged as an advanced solid-state surface engineering technique for tailoring high-performance surface architectures in metal matrix composites (MMCs). By combining localized thermo-mechanical deformation with controlled material flow, FSP enables grain refinement, homogeneous dispersion of reinforcement, and strong interfacial bonding without melting or altering bulk properties. This review critically examines the role of FSP in enhancing the mechanical, tribological, and corrosion performance of composites, with emphasis on process–structure–property relationships. Key strengthening mechanisms, including grain boundary strengthening, load transfer, particle pinning, and defect elimination, are systematically discussed, along with their implications for wear resistance, fatigue life, and durability. Special attention is given to corrosion and tribo-corrosion behavior, highlighting electrochemical mechanisms such as micro-galvanic interactions, passive film stability, and interfacial chemistry. Furthermore, the eco-efficiency, industrial viability, and sustainability advantages of FSP are evaluated in comparison with conventional surface modification techniques. The review concludes by identifying critical challenges and outlining future research directions for the scalable, multifunctional, and sustainable design of composite surfaces.

The use of aluminium alloys in internal combustion engines is an effective strategy for increasing energy efficiency, reducing component mass, and lowering harmful gas emissions. This paper analyses different types of Al–Si alloys (hypoeutectic, eutectic, and hypereutectic) in the context of their use in the production of engine blocks, pistons, and cylinder liners. Special attention is given to the tribological challenges of using aluminium, such as increased wear and lower strength compared to traditional materials such as cast iron. Modern methods for improving wear resistance are discussed, including alloying, the application of solid lubricants and protective coatings (Ni–SiC, Al₂O₃, MoS₂, etc.), and advanced surface engineering technologies such as PTWA, HVOF, and laser alloying techniques. This paper also presents practical examples of industrial applications, highlighting their essential role in the development of lightweight, high–performance internal combustion engines. This review highlights that the combination of optimized alloy composition and advanced surface engineering technologies represents the most effective approach for enhancing the durability and tribological performance of lightweight engine components.

Planetary gear trains represent a special type of gear transmission whose element motion resembles the movement of planets around the Sun. Thanks to their compact design and the ability to achieve high transmission ratios with a relatively low total mass, they have found application in various fields of mechanical engineering. The basic planetary gear train (PGT) consists of two central gears (one with external teeth and the other with internal teeth), planet gears, and a carrier on which the planets are mounted. By connecting the appropriate elements to the input and output shafts, as well as by fixing certain components, different configurations or planetary gear train schemes can be obtained. This is described in the literature [1] and [2]. By adding gears and carriers to the structure of a simple planetary gear train, complex planetary gear trains are formed. Their advantage over simple ones lies in achieving a greater number of different transmission ratios. This has defined the wide application of PGT in automatic transmissions of various passenger and heavy-duty vehicles, as well as buses and construction machinery. To determine the transmission ratios, or the speeds of a multi-stage planetary gear train, it is necessary to understand the kinematics of the coupling between its elements. Considering the complexity of the motion, this represents a very challenging task. In books [1, 2], the most commonly used methods for solving the kinematics of PGT are presented.

Existing methods for selecting the number of teeth in complex planetary gear systems are often methodologically demanding. They do not always ensure all conditions required for proper operation and assembly. This paper presents an analytical methodology for determining gear tooth numbers. The method is demonstrated on a Ravigneaux planetary gear set with seven kinematic links and two degrees of freedom. It ensures the simultaneous satisfaction of all meshing and assembly conditions. Starting from the known transmission ratios, the number of teeth of one central gear, and the selected angular displacement of the outer planet gear, analytical relationships are derived. These allow the determination of the tooth numbers of all remaining gear elements. The procedure is implemented in Python 3.13. This enables a systematic evaluation of predefined input ranges and an automatic verification of geometric constraints, including interference and undercutting conditions. The proposed method yields six feasible configurations. Compared with the Borg-Warner M85 automatic transmission, deviations in individual gear ratios reach up to 10%. Significantly lower tooth numbers are achieved for several gears. These results suggest that the proposed methodology can achieve comparable kinematic performance while offering more compact gear designs and a potential weight reduction. The developed model also provides a basis for extension to more complex configurations and integration with optimisation and dynamic criteria in planetary gear synthesis.

This study investigates the application of experimental design methods in optimizing the efficiency of a single-stage worm gearbox, with the CCD method being used to achieve maximum efficiency. The experiments were conducted on the AT200 device, considering rotational speed, lubricant type (VG220) and experiment duration as key factors. The optimization of efficiency was performed using the CCD method, and the results were analyzed through ANOVA. The findings indicate that rotational speed is a more influential factor compared to operating time, with the highest efficiency values recorded at the maximum rotational speed (≈1603.5 min⁻¹) and an operating time of 10 minutes. Mathematical models were developed with a 95% confidence level, enabling the prediction of efficiency based on the examined factors.