Subject reviewStrict requirements that are put on mechanical constructions from the aspect of increase of exploitation periods and reduction of their weights, therefore of their prices as well, implicate developments and applications of new composite materials with matrices of lightweight metals. Composite materials with metal matrices are used for engine cylinders, pistons, disc and drum brakes, Cardan shafts and for other elements in automotive and aviation industry. The most important type of metallic materials is composite materials with matrices of aluminium alloys due to a set of their beneficial properties. Improvement of mechanical, especially tribological properties of hybrid composites were provided by the use of certain reinforce materials such as SiC, Al2O3 and graphite in defined weight or volumetric share. New developed hybrid composites with aluminium matrices have significantly higher resistance to wear, higher specific stiffness and higher resistance to fatigue. By the increase of quantities of produced elements made of hybrid composites, decrease of their prices is induced that even further enlarge their applications. The applications of aluminium hybrid composites are considered from the aspect and with the focus on automotive industry. Keywords: aluminium; application; automotive industry; composites; MMC Primjena aluminijskih hibridnih kompozita u automobilskoj industrijiPregledni članak Pooštravanje konstrukcijskih zahtjeva s aspekta povećanja radnog vijeka i smanjenja mase, a samim tim i cijene konstrukcije, iniciralo je razvoj i primjenu novih materijala s osnovom od lakih metala. Kompoziti s metalnom matricom nalaze sve veću primjenu pri izradi košuljica cilindara motora, klipova, kočionih diskova i doboša, kardanskih vratila kao i drugih dijelova u automobilskoj i avio industriji. Posebno mjesto, od svih metalnih materijala, zauzimaju kompoziti na osnovi legure aluminija zbog niza dobrih svojstava. Poboljšanje mehaničkih, a posebice triboloških karakteristika hibridnih kompozita moguće je uporabom određenih ojačivača, najčešće SiC, Al2O3 i grafita, u odgovarajućem masenom ili volumenskom udjelu. Novodobiveni hibridni kompoziti s aluminijskom osnovom imaju znatno povećanu otpornost na habanje, povećanu specifičnu krutost i povećanu otpornost na zamor. Povećanjem količine proizvedenih dijelova od aluminijskih kompozitnih materijala dolazi do smanjenja cijene ovih dijelova, što dodatno povećava područje njihove primjene. U radu su prikazani primjeri primjene aluminijskih hibridnih kompozita s osvrtom i težištem na automobilskoj industriji.

A new design of a two-stage cycloidal speed reducer is presented in this paper. A traditional two-stage cycloidal speed reducer is obtained by the simple combination of single-stage cycloidal speed reducers. A single-stage reducer engages two identical cycloid discs in order to balance dynamical loads and to obtain uniform load distribution. Consequently, the traditional two-stage reducer has four cycloid discs, in total. The newly designed two-stage cycloidal speed reducer, presented in this paper, has one cycloid disc for each stage, that is, two cycloid discs in total, which means that it is rather compact. Due to its specific concept, this reducer is characterized by good load distribution and dynamic balance, and this is described in the paper. Stress state analysis of cycloidal speed reducer elements was also realized, using the finite elements method (FEM), for the most critical cases of conjugate gear action (one, two, or three pairs of teeth in contact). The results showed that cycloid discs are rather uniformly loaded, justifying the design solution presented here. Experimental analysis of the stress state for cycloid discs was realized, using the strain gauges method. It is easy to conclude, based on the obtained results, that even for the most critical case (one pair of teeth in contact) stresses on cycloid discs are in the allowed limits, thus providing normal functioning of the reducer for its anticipated lifetime.

The paper deals with the considerations related to the basic properties and application of primarily aluminum alloys and composite materials for different purposes with the focus on the automotive industry. Through the description of the basic characteristics of aluminum alloys, the starting points for their application in different technical systems are given. On the other hand, the advantages and disadvantages of the use of certain aluminum alloys, along with the guidance and compounds and elements whose use is further enhanced and enriched by aluminum alloys, are predominantly presented. The application of aluminum alloys in the automotive industry, as well as the particular types of aluminum based materials used for individual aggregates and circuits of motor vehicles, as well as their behaviour in different operating modes are imposed as a key chapter of the work. Ultimately, the advantages that are primarily achieved with the vehicle are obtained by the use of aluminum alloys and composites, with the conclusion that there is still space in the field, further improvement of the characteristics of aluminum alloys, and in the field of expansion of the diapason of their application.

Biomimetics, biomimicry and bionics are synonyms for the scientific discipline of creating new structures inspired by nature. Biomimetics systematically analyses the evolutionary processes of living organisms, their structural relationships, the characteristics of natural materials and it studies how this knowledge can be used to create the optimal products and new sustainable materials. In the past decade, the biomimetics has received an incentive for the development by the technology modernization, and above all, by making it possible to study the microand nanolevels of biological structures. On the other hand, the miniaturization of technological devices has increased the need to understand the tribological phenomena on micro-and nanolevel, where is a huge potential for technological innovation. The integration of advanced research methods made it possible to discover new aspects in the structure and properties of biological materials and transfer that knowledge into new concepts or products. State-of-the-art of biomimetics progress is discussed, as well as, its goals and the potential to simultaneously achieve the financial and ecological contribution by realization of bio-inspired concepts. An overview of biomimetic researches is also provided, with special emphasis on the possibility of their tribological applications. The characteristic examples have been presented and those examples show how the structural and mechanical properties of the material were used as the basis for developing new creative solutions to solve the problem of friction in engineering applications.

This paper analyses the influence of graphite reinforcement, load and sliding speed with constant sliding distance on tribological behavior of A356 aluminum matrix composites reinforced with 10 wt.% silicon carbide and graphite using the Taguchi design. Hybrid composites were produced in the compo-casting process. Tribological tests were performed on a block-on-disc tribometer where the weight percentage of graphite has three variations (0, 3, and 5), as well as load (10 N, 20 N, and 30 N) and sliding speed (0.25 m/s, 0.5 m/s, and 1 m/s), with sliding distance of 300 m. The wear of the composite is investigated under dry sliding condition. The specific wear rate was analyzed using Taguchi method with the aim of finding the optimal parameters. By applying analysis of variance, it was determined that the best tribological properties has A356/10SiC/3Gr hybrid composite. It was also found that the greatest impact on specific wear rate has load with the percentage effect of 69.163%, then sliding speed with 14.426% and the interaction between wt.% graphite and load. The dominant wear mechanism is adhesive wear as confirmed by scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS).

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Purpose This research aims to describe the influence of weight per cent of graphite (Gr), applied load and sliding speed on the wear behavior of aluminum (Al) alloy A356 reinforced with silicon carbide (SiC) (10 Wt.%) and Gr (1 Wt.% and 5 Wt.%) particles. The objective is to analyze the effect of the aforementioned parameters on a specific wear rate. Design/methodology/approach These hybrid composites are obtained by means of the compo-casting process. Tribological analyses were conducted on block-on-disc tribometer at three different loads (10, 20 and 30 N) and three different sliding speeds (0.25, 0.5 and 1 m/s), at the sliding distance of 900 m, in dry sliding wear conditions. Optimization of the tribological behavior was conducted via the Taguchi method, and ANOVA was used for the analysis of the specific wear rate. Confirmation tests are used to foresee and check the experimental results. Examined samples were analyzed via a scanning electron microscope (SEM). Regression models for predicting specific wear rate were developed with Taguchi and ANN (artificial neural network) methods. Findings The biggest impact on value of specific wear rate has the load (43.006%), while the impact of Wt.% Gr (31.514%) was less. After comparison of the results, i.e. regression models, for predicting the specific wear rate, it was observed that ANN was more efficient than the Taguchi method. The specific wear rate of Al alloy A356 with SiC (10 Wt.%) and Gr (1 Wt.% and 5 Wt.%) decreases with a decrease in the load and weight per cent of Gr-reinforcing material, as well as with a decrease in sliding speed. Originality/value The results obtained in this paper using the Taguchi method and the ANN method are useful for improving and further investigating the wear behavior of the SiC- and Gr-reinforced Al alloy A356.

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