International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

Analyzing the current state of the road infrastructure in Bulgaria, it should be emphasized that it is the result of the long-term preferential and large-scale industrialization of the national economy. This policy, until the beginning of democratic changes in the country, put the development of the road infrastructure on the back burner, due to the limited resources and the set priority. Investment during the transition years is characterized by irrationality, mainly due to the lack of a justified, detailed developed and provided with financial resources long-term plan in this area. Bulgaria’s accession to the European Union led to a rethinking of the content of the state infrastructure policy, a change of views and the need for rapid integration of the national transport system with the European one. The development of the transport infrastructure plays an important role in strengthening the ties between European countries and in the inclusion of new member states of the European Union. The country’s road infrastructure affects the competitiveness, economic growth and employment of the working population. This report examines and analyzes the changes and modifications that have occurred in the structure, condition and density of Bulgaria’s road infrastructure for the period 2007 – 2024. The main goal is to derive recommendations and guidelines for the future sustainable development of the country’s road network based on the analysis of the development of the road infrastructure during the first eighteen years of Bulgaria’s membership in the European Union.

For various canonical forms (plane, cylinder, ball, etc.), a generalized mathematical model (MM) of a nonlinear steady-state process of molecular heat transfer (or moisture diffusion) through enclosing structures (ES) is proposed, taking into account infiltration or exfiltration of a vapor-air (gas) mixture and the presence of various internal or surface positive (moisture condensation) or negative (evaporation of moisture) of heat sources (HS). The mathematical formalization of the posed boundary value problem (BVP) of transfer and its general solution are given, on the basis of which, under various specified conditions of unambiguity, solutions of specific physical processes with constant or variable thermophysical characteristics and HS are constructed and analyzed. For large-scale transitions, the short-circuit problem is posed and solved under various boundary conditions (BVC), written in a criterion form as dependences of the dimensionless temperature T(R-, Pe, Po) on the dimensionless thermal resistance (R-) of the heat exchange criteria for the similarity of Pecle (Pe) and Pomerantsev (Po).

The paper is a continuation of research dealing with the structural design of the manipulator of the bulk material rotary valve based on the specifications of a food company. This issue is currently immensely topical for reasons such as increasing safety, speed, or efficiency of work. In the previous publication, the authors focused on determining the position of the center of gravity of the rotary valve due to the fact that this essential data is not provided by its manufacturer. Accordingly, the present work attends to the design of the steel structure of the trolley and the path along which the trolley in conjunction with rotary valve will move. The structural design is analyzed in the paper by means of analytical functional and dimensional calculations. On the basis of the parameters of the calculated centers of gravity of the individual components of the structure, the reactions from the track on which trolley travels to the weight transmitted by the prismatic wheels of the trolley were determined. The loads were calculated in transverse and longitudinal directions. In addition, reactions from the individual wheels were determined for the case, when the rotor valve is in a position with the rotor retracted (operating position). The achieved results demonstrate that the least favorable case for the stresses on the track travel of trolley occurs in the case with the rotor retracted. Furthermore, the calculation of the loads acting on the track beam in the most unfavorable position of the trolley was performed. Moreover, the resistive forces acting on the trolley were analyzed. The results indicate that the use of this mechanism will be feasible in operation.

Nanotechnology has grown in popularity due to the enormous potential for producing materials and products with diverse properties, allowing significant advancement of existing technology and the development of new innovative technologies. Nanomaterials behave differently at the nanoscale than their conventional counterparts, opening exciting new possibilities in a wide range of construction applications. Nonetheless, the lack of information on nanomaterials’ suitability, high costs, and health risks limits their use in construction and structural engineering. As a result, research must be conducted to provide accurate information and facts about the properties and performance of nanomaterials under various load conditions, as well as information on the advantages of using nanomaterials over other construction materials. This paper provides information on nanomaterial properties and how they affect structural materials’ microstructure and mechanical properties. It also demonstrates the benefits of using nanotechnology and suggests new possibilities.

In recent years, 3D printing has gradually appeared in people’s field of vision. The addition of wood in thermoplastics improve their some mechanical properties such as tensile and bending modulus without affecting its biodegradability. The decrease in the cost of filaments may enlarge the utilization of biodegradable filaments after the disposal in near future. Small-scale elements used in furniture production, such as connector fittings or fasteners for shelves, may give functional and structural properties without significant investment. 3D-printed connections are suitable when the the production complex shaped connectors and quick disassembly are required, to reduce the product’s weight and price

The mechanical properties bending strength and modulus of elasticity in bending of a new type plywood for construction, based on black locust wood, have been investigated in relationship with the bonding technological factors. The experimental investigation is based on an optimal composite design with four control factors – temperature, pressure, bonding duration and specific glue consumption. Regression models describing the dependence of bending strength and modulus of elasticity in bending on the investigated technological bonding parameters are estimated. The obtained experimental and model-based results are analysed and discussed

The paper deals with the problem of joints of car parts of the car construction. The construction of the car must meet the emission standards, in order to meet them it is necessary to reduce the weight of the car while maintaining strength and durability. Therefore, different materials are used in the design of car construction, such as different types of steels, aluminum alloys, composites and plastics. This increases the demands on the car construction and on the type of sheet metal joining technology used. The paper deals mainly with glued and welded joints in the design of car construction. The suitability of individual types of joints is solved using the finite element method.

Digital platforms for education are one of the newest and most effective online tools for collaboration and knowledge accumulation. The construction industry could benefit from such a platform to prepare a new generation of building entrepreneurs. The webbased platform has many advantages like creating new ecosystems of data, information, knowledge, people, processes and things. Therefore, the article entitled Digital Platform for Building Entrepreneurial Skills and Competitiveness in The Construction Sector presents a modern way of obtaining business skills. It models an affordable, user-friendly digital system for learning and teaching the best practices in the construction industry.

The project to build a second nuclear power plant in Bulgaria emerged in the 70s of XX century. He repeatedly starts and stops over the past decades, mostly under the influence of external and internal policy decisions. Meanwhile, Bulgarian taxpayers pay large sums for errors and indecision of our political elite. Time specialists in this area say their arguments and take the best decision for Bulgaria instead of wasting money without end.

One of the greatest benefits when using these alternative building methods to construct affordable homes is the speed of erection.
Delivery of units will be maximized while the quality will also be improved. At the moment one of the biggest problems with the RDP houses is the speed of delivery which causes the housing backlog in South Africa. This system has developed into a construction technology that addresses eight key challenges embodied in the low cost and affordable housing shortages facing developing and design tables to aid rapid selection of light steel sections, depending on the span, the loading and the steel grade used.