Scientific activity of A. Sładkowski began in high school years, when in 1971 he took part in a scientific conference of young scientists, which was carried out in Kiev.

His scientific activity continued in the students' years. He took part in student’s scientific conferences at Dnepropetrovsk State University in 1976 and 1977. Reports, which was presented, and his degree work (1978) was devoted to the problems of contact interaction of elastic bodies.

These studies have been devoted to the study of phenomena microslip. Contact problems considered both theoretically and experimentally. For modeling of microslip during rolling of cylindrical bodies methods of complex variable theory [1, 3] and finite element method [2] were use. Experimental verification of the results was performed using strain gauges [1, 3, 9, 12] on special experimental devices [6, 14].

The problems of the determining of microslip zones during compressive and shear of elastic rectangle were solved with the help of techniques developed based on FEM [5, 11, 25]. In carrying out experimental studies was seen the effect of the reinforcement on low modulus materials by strain gages were seen.

The method for correction of the strain gages records was proposed on the basis of the calculation using the FEM. Later this technique became the basis for the development of special tensometric beams capable to set the large deformation, while remaining in the elastic zone [7, 17, 42].

Collective research work "Investigation of microslip effect in friction joints", which was awarded the first prize of VSNTO (All-Union Council of Scientific and Technical Societies) [10] in 1983, as well as dissertation for the degree of candidate of physical and mathematical sciences (PhD, defended in 1987) [18, 19] contained a synthesis of the research stated above.

Another direction of research in these years has been the study of shell structures, which are used for the manufacture of flying machines. The experimental techniques developed above (strain gauging) and theoretical research (FEM) [4] or shell theory [13, 16] were used. The measurements only in selected places were the lack of strain gauging, because not to allow to get a complete picture of the entire deformation of the object.Holographic interferometry allows to eliminate this drawback and allows to carry out high-precision measurements. But its drawback was the fact that the obtained interferogram need to decrypt, replacing the interferential portrait by displacements distribution on the object surface. The developed technique by deciphering interferogram and calculation of shells made from composite materials was described in papers [8, 15].

In the case of solution of the stated above tasks of decoding the problem of the numbering fringes determining arises for subsequent conversion into the displacements of the corresponding surface areas of the shell. The fairly simple experimental technique, which allowed to determine the interference fringes numbering [20, 21], was offered.

Since 1987 A. Sładkowski worked in Dnepropetrovsk Metallurgical Institute (DMetI, currently National Metallurgical Academy of Ukraine - NMetAU). Subjects of research has been slightly modified to give character associated with metallurgical products, in particular for rail transport (wheel and rail). Corresponding group of researchers led by prof. V.P. Yesaulov.

The technique for calculation of disks of solid wagon wheels was developed using the theory of shells of revolution [30] in collaboration with scientists of well-known Kiev school from the Institute of Mechanics of NAS of Ukraine, headed by academician J.M. Grigorenko. The method of calculating of the wheels with flat disks of constant thickness was also developed. This methodology is based on the use of functions of a complex variable. These disks are used for crane wheels [22, 31].

In view that the railway wheel can be considered as a axisymmetric object of research under action of non-axisymmetric load, for simplifying the calculations with using of limited capability computers, the use of semi-analytical FEM was proposed [24, 35, 36, 55].

Under the conditions of the limited capacity for generation of finite element meshes, the number of elements through the thickness of the wheel disk was of great importance. Evaluation of the accuracy of solution was possible by comparing the numerical solution using FEM and analytical method [32, 33, 90].

Another area of research of A. Sładkowski was the study of contact interaction in a pair of wheel - rail. For this was developed quasi-Hertz approach whereby able to estimate the location of contact zones and stress values in this areas with the presence of one or two contact zones ("single-point" or "two-point" contact) [28, 46, 50, 52, 60, 72, 80].

It is obvious that one of the causes of wear of wheels and rails was the discrepancy of profiles of working surfaces of wheel and rail. Numerous changes introduced to the constructions of the wheels and rails, as well as to the constructions of the railway tracks as a whole, was often without result to wear reduction. On the contrary, many of the changes in the railway sector has led to catastrophic wear of wheels and rails in the 80s - 90s of the twentieth century on the railway system of the USSR, and then of the CIS. A.Sładkowski studied these changes and their impact on the wear, accordingly [23, 34, 48, 54, 61]. It should be noted that the wear of the wheels was studied as for industrial transport [72], so and for the main transport [71, 72]; as for passenger or freight transport [74, 84], so and for tractive rolling stock [85, 94].

Working capacity of wheels and rails depends on the metal from which they are made, processing technology and other aspects that can be studied by a metallographic analysis of these objects. These studies were conducted in collaboration with a group of scientists of DMetI headed by academician of NAS Yu.N. Taran, and then prof. S.I. Gubenko. Joint research of wear processes for wheels and rails, including an extensive analysis of the microstructure of wheels steel, contributed to the creation of rational designs of wheels and rails [29, 51, 56, 63, 64, 70, 81].

Thus, on the basis of theoretical calculations, of the analysis of the stress-strain state of a pair of wheels - rail, of the numerical simulation, of the metallographic analysis, of the measuring of wheels and rails wear in industrial and mainline railway transport, was created a number of new designs of wheels and rails, the novelty and effectiveness of them has been confirmed by inventor's certificate and patents [26, 27, 44, 47, 57, 78].

More wear-resistant profiles of railway wheels, which was offered, needed in new technological solutions and new tools for carrying out of regenerative repair of the wheels of wagons and locomotives in depot conditions. Development of a full set of tools (copiers, templates and contra templates) for different wheel turning machines [43, 62, 75, 77] and of the profile cutters for machine KZh-20 of different modifications [41, 50, 65, 68, 75, 77] enabled to introduce the new wheels not only into experimental, but also into the commercial (industrial) operation.

Certain barrier to the introduction of new developments was the need to prove their safety in dynamic interaction between track and rolling stock. Studies of the said dynamic and the simulation of the motion as of a single wheelset with the new wheel profile as well as of bogies negotiation have been conducted [49, 58, 59]. A. Sładkowski participated in field dynamic tests carried out by DIIT employees. It should be noted also complex character of studies of railway wheels with using FEM, which allowed to take into account the dynamic effects on the wheels [66, 69, 70, 76, 82].

Significant economic effect obtained under actual operating conditions of mining and processing enterprises, metallurgical plants and a whole number of depots of several mainline railways, served as proof of the effectiveness of the proposed constructional solutions. The above scientific, technical and technological solutions served as the basis for writing a dissertation for the degree of doctor of technical sciences (doctor habilitatus) [73, 74].

The complex character of the conducted researches, the developed methods and technologies provided a basis for the application of this approach to other technical objects. In particular, was studied rope blocks and drums, and their interaction with the ropes. These researches were used for writing several papers and patents dealing topics of materials-handling equipment [37, 38, 39, 40, 45, 53].

Another subject of scientific research by A. Sładkowski were gear transmissions. Research of contact phenomena with using FEM have been successfully applied to the study of the stress-strain state at the teeth contact of involute gearing [79, 83, 87, 101].

Since 2000 the scientific activity of prof. A. Sładkowski associated with Silesian University of Technology. This did not mean of a fundamental change in direction of research or a radical change of scientific contacts. Certain changes were connected with relatively large capabilities of computing equipment in Poland or potentialities of application of experimental techniques for the measurement.Exchange of experience of research of Ukraine and Poland was mutually beneficial and favoured the development of scientific relations, the development of new methods of research and the expansion of the field of scientific activity. For example, studies of the effect of thermal stresses in shoe braking of wagon wheels were started by prof. Sładkowski still in Ukraine on request of the Indian Railways and was continued in Poland [106, 109, 116, 118].

Using of FEM for solving contact problems has certain limitations. The problem is that the contact problem with previously unknown contact area belong to a class of essentially nonlinear problems. Their solution requires the use of iterative approaches that can be difficult to do if there is a very dense grid (spatial). Testing were made with the classical solutions and new methods for solving of contact problems was developed for relatively rare coordinated FE meshes [125, 160].

Studies of contact interaction of the wheels and rails had some distinctions with previous similar studies in Ukraine because the studies were made on other profiles of wheels and rails, including real, which got as result of experimental scanning of worn out wheels and rails [114, 123, 126, 133, 134, 137, 141, 145, 148, 149, 150, 166].

The most significant work devoted to the calculation of the contact stresses in the pair wheel - rail using FEM was an article [152], which was published in the journal Wear in 2005. According to the list of citation of database Scopus it cited 37 times and the number of citations is increasing year by year.

In articles [158, 185] prof. Sładkowski continued modeling of phenomena microslip using FEM. It is also obvious that the above contact phenomena have great influence on the wear [205, 295].

In his studies of contact interaction of wheels and rails prof. Sładkowski continued interaction with the Dnepropetrovsk school of metallurgists and metallographers. Comparative analysis of the metal structure in the near contact zone allows to check the conclusions of FE calculations [139, 146, 151, 164]. The monograph [153] is certain summary of many years of research of contact interaction between wheels and rails.

Railway wheels have also other stress field conditioned by the contact interactions, which arises as a result of pressed connections wheel and axles or shrink fitting of bandage on wheel center (for composite wheels). These processes are very responsible, since they determine the safety of operation of the rolling stock. These processes and the stress fields obtained as results were analyzed in articles [91, 92, 93, 97, 100, 112, 233].

The study of the influence of the FE mesh generation on the accuracy of the solution not only for contact problems, but also for railway wheels in general, was also continued [103, 112, 121].

The complex character of the calculations of the wheels by means of FEM, which allows to take into account the different types of loading, became the basis for the analysis of the stress state of the wheels of various designs [95, 102, 124, 130, 131, 161]. It gave ability to estimate the ultimate limit state of wheel pairs [244, 284, 289]. The results of calculations of the wheels using FEM verified experimentally in laboratory tensometric tests [104, 120, 162].

Since 2000, research of gears in using of FEM were continued. The object of research was changed. These were the gear transmissions of locomotives [122, 127, 129, 135, 142, 147, 165]. The traction drive of locomotive on the whole was also considered [191, 192, 196, 230].

Numerical methods were also used for solving of the dynamics problem of the rolling stock. This was done by analysis relatively of small models (with a small number of degrees of freedom) and a very serious of models of carriages and tracks of taking into account the various types of track irregularity, which were modeled using modern application packages ADAMS/RAIL, UM, Medina, Vampire et al. [96, 99, 105, 108, 111, 115, 128, 136, 156, 157, 163, 182, 278, 297].

Another direction of research associated with the rolling stock was due to the cooperation with the East Ukrainian National University named after V. Dahl (VUNU). The employees of this university offered new constructions of friction vibration dampers for railway wagons and locomotives. The above written methods of calculating the contact interaction with using FEM have been successfully applied to the analysis of the coupled problem of thermoelasticity for frictional interaction of damper elements [168, 169, 174, 175]. At the same time the technological problem of the plastic deformation of thick plate billet was solved, that was necessary to ensure of the production of damper parts [159, 170].

Analysis of thermal stresses arising in the parts of dampher during its dynamic work, leads to the need of usage of powerful computers. One way of solving this problem is the parallelization of computations. MSC.MARC gave an opportunity of domain decomposition, which made the computational process more efficient [236, 247, 249].

Rolling stock is not the only object of railway equipment, where are used methods developed or used by prof. Sładkowski. In particular, these techniques were used to analyze the stress state of parts for the turnouts [138, 143, 144, 154, 173]. These techniques were also used to design of the measuring device designed for adjustment of the turnouts.

Research was also conducted to analise the stress-strain state of welded rails at their interaction with rail fasteners. There was taken into account the thermal loading of the rails, as well as contact interaction with the wheels of the rolling stock [180, 181, 301, 309, 313, 326, 335]. When analyzing of the fixed rails to the sleepers was necessary to have data on the mechanical properties of elastic pads. For this purpose was carried out experimental studies and calculations using the FEM [183, 194, 198].

Masts of traffic lights are infrastructure of rail transport also. Calculations based on the use of the FEM was perform also [155, 167, 172].

It is clear that the developed methods were used to analyze the stress-strain state not only rolling stock or transport infrastructure. For example, the elastic couplings was studied in papers [176, 177], parts and components of materials-handling equipment in [201, 204, 231, 232] or the means of factory transport in [203].

Materials-handling equipment needs in the calculation of dynamic systems also. In [171, 210, 211] was simulated dynamics of bridge cranes. These studies were conducted in conjunction with FE calculations described above. In [258] investigated the joinings of conveyor belts used in conditions of mining and processing enterprises. The correctness of the modeling and analysis finally effect on the operation safety of vehicles [262].

Great attention in the articles A. Sładkowski paid to the analysis of mining machines [331, 332, 333], methods of transportation in mines [306, 314] or open quarries [329].

Prof. A. Sładkowski in 2006 changed own place of work for Department of Logistics and Industrial Transportation. He headed this Department in 2009. This transfer had contributed to his interest with the problems of logistics. This led to the fact that every year an increasing number of papers were devoted to logistics, which are made by him as a co-author and independently. In his works of prof. A. Sładkowski considering various logistical problems that often bordered with the other branches of science.

For example, for the Kazakh Railway the biggest problem is the unloading of tanks with viscous oil. Particularly acute problem stands in the winter. Joint with KazNTU solutions was published in [238, 251, 255], that will help to solve this problem.

In articles [197, 219, 220, 224, 229, 235, 259, 305, 307, 328, 334] analyzed the railway transportation on the route East - West. Here was analysed the reasons are relatively low functioning capacity of railways. There were shown "bottlenecks" and ways for solving these problems. The problems of control of the railway transport [276, 280, 300, 324, 325], intelligent transport systems [304, 310] or transportation of products of the coal industry on the territory of Poland by means of rail and road transport [237] had also been considered.

In the works of A. Sładkowski much attention is paid also to road transport. The issues of transportation of non-standard goods [189], the issues of automatic payment collection for freight transport and their impact on the logistics of transport companies [243, 257, 321], the use of motor vehicles in the deep open pit [267, 298, 308], the use of on-board measurement systems on cars [274, 277], control weight of vehicles [283], quality of pavements [296] are analysed.

A significant place among the works of A. Sładkowski dedicated logistics occupy articles related to industrial and factory transport. For example, various aspects of application of transport at shipyards [179], the use of loaders in ports [275], the problems of optimizing of the warehousing [234, 268, 286, 291, 293], the rationalization of transport processes for the food industry [272], metallurgical industry [209], coal-mining industry [215] or for individual enterprises and companies [202, 212, 225].

In his works Sładkowski gave much attention to analysis of regional transport and logistics problems [178, 214, 241, 285], for methods of planning of goods deliveries [207, 240, 261, 292].

At the present time problems of recycling and utilization have great importance. And if this topic is quite developed for motor vehicles, however it is still quite a new direction for the means of industrial transport [208, 216, 239, 242, 253].

Another new area of research of A. Sładkowski was the task of utilization of CO2. For the Polish energetic sector it has a great significance. Its logistical aspects were considered in papers [217, 226].

It should be noted that logistics has many directions and it is quite obvious that any scientist can‘t work in all aspects. Nevertheless, among the works of A. Sładkowski there are many articles on the general problems of logistics, transportation management and other scientific aspects [216, 218, 223, 228, 256, 260, 263, 269, 270, 282, 330].

Prof. A. Sładkowski is editor-in-chief or editorial board member, chairman or member of the scientific and program committees of many scientific conferences and journals. He shares his experience in methodical articles, for example, [288].

In 2010-2013 he was the chairman of the scientific council of the Research and Development Centre of Hoisting Machinery and Mechanical Conveying Equipment "DETRANS".

During his scientific career prof. A. Sładkowski repeatedly received the award of rectors: Dnepropetrovsk State University (1983); National Metallurgical Academy of Ukraine (1988); Silesian Technical University (2005, I degree; 2011 III degree; 2013, II degree; 2015, III degree).

Scientific activity of A. Sładkowski was highly appreciated at the international level. In 2013 A. Sładkowski was elected a full member (academician) of the Russian Academy of Transport. He cooperates with Ural Branch of RAT.

In 2015 East-Ukrainian National University named after V. Dahl awarded A. Sładkowski the title of doctor honoris causa of EUNU.

In 2016 he was accepted as a member of the Union of Scientists in Bulgaria. In addition, in 2016 he was accepted to the Federation of Scientific and Technical Unions in Bulgaria as a member of the Club of Mechanical Engineers (territorial organization of scientific and technical experts in Rousse).

In 2017 he was elected a Honorary Member of Scientific Council of Institute of Machine Mechanics of Georgian National Academy of Sciences (GNAS).

Thus, the range of research interests and experience in scientific activity for prof. A Sładkowski is sufficiently broad. To achieve results described in articles and monographs, he interacted with various experts, organizations and enterprises, and he is open for such mutually beneficial cooperation in the future.

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