Applied Engineering Letters

115-123

Authors: L. Ramesh, P. Srinivasa Rao

In this paper, a new modal parameters-based damage detection method has been proposed for accurate characterization of single and multi-surface cracks in beam-like structure. The advantage of this method is undamaged mode profiles from the damaged mode profiles of beam structure. For that, curve fitting (CF) analysis was used to extract the undamaged mode profiles from damaged one. Discrete Wavelet transformation (DWT) method is presented to demonstrate effectiveness of the proposed approach without use of base line data as a reference. To illustration of this method, numerical and experimental modal analysis is performed on two aluminum cantilever beams containing single and double cracks to examine the location and quantification of different damage scenarios. First five modal frequencies and mode profiles are employed to assess the effectiveness of the proposed method. Moreover, to validate the accuracy of the proposed approach in damage identification, established results have been balanced with other experimental based results, which were found in the literature. From the results, it can be seen that damage scenarios of the two beams are quite different the chosen methods precisely identify the location and quantification of the damage in beam structures. It is concluded that composed mode profiles by the proposed approach can be conveniently used as reference data for the damage identification purpose.

129-134

Authors: J. Skerlic, D. Nikolic, D. Cvetkovic, A. Miškovic

Solar energy is the most abundant, inexhaustible and clean of all the renewable energy resources till today. Solar energy has received much more attention in building energy systems in recent years. During the first years of the twenty-first century, extensive efforts have been undertaken to alleviate global warming of the earth caused by emission of CO2 in atmosphere. These emissions are generated by intensive burning of fossil fuels to satisfy the growing energy needs of humanity. The emissions may be mitigated when part of energy needs is satisfied by using non-polluting energy sources such as solar energy, instead of fossil fuels. In households, customary is to use electricity for heating of DHW. Most of electricity is produced by using coal with high greenhouse emission. Accordingly, worldwide, the most rewarding application of solar energy is when it replaces electrical energy for heating of DHW in households. The solar collector has to take the optimal position that will guarantee the highest generation of heat. Optimal positioning must be based on rigorous calculations and not on the basis of experience. Such calculations lead to the improvement of the operation of solar energy systems. This paper gives a review of research with the objective of presenting, classifying and analysing the different criteria by which the authors observed an optimal position of the solar collector. In addition, it is important to have a high efficiency of conversion of solar energy to heat. Then, the highest amount of avoided primary energy, avoided electrical energy, avoided exergy, and decrease in CO2 emissions may be expected.

85-89

Authors: Dj. Dihovični, V. Krunić

In this paper it is presented creation and encryption of e-commerce database for selling mechanical elements. It is shown a procedure of creation a database and tables with appropriate data, which is the first step in developing stable e-commerce application. For security reason it is necessary to encrypt the database, and it is described a complete process, and as well it is given part of the code of web application for inserting data into the tables, deleting some data and updating them. In developing ecommerce application for selling mechanical parts, it is applied C# programming language by using ASP.NET, with using HTML language and XML.

98-104

Authors: A. Ilić, L. Ivanović, B. Stojanović, D. Josifović, E. Desnica

Impact toughness of samples with three different relative positions of V-notch and multipass V- butt welded joint at high-strength low-alloy steel S690 are considered in this paper. The aim of this paper is to analyze the influence of material degradation due to welding to impact toughness of samples made of considered steel. Impact toughness was analyzed by experimental approach objected to including as many influential factors as it is possible. The main objective of impact toughness testing is to evaluate the influence of welding to overall load capacity and stability of welded mechanical construction made of high-strength low-alloy steels. Fully understanding of transformation processes provoked by welding of high-strength low-alloy steels and impact toughness testing as resulting property of those processes are crucial to perform integrity, safety and reliability analysis. This paper pointed out the necessity of analyzing the welded constructions on different dimension levels. Further investigations in this area have to be a continued through more quantitative analysis of welded joints which will, established precise analytical model of zones of welded joints, and furthermore, in involvement with adequate software, a complete evaluation of the experimentally obtained results. As experimentally obtained results of impact toughness that correlate to microstructure and microhardness distribution implicated that development of those steels must be followed with improving weld processes and development, adjusting and modification of the design.

47-51

Authors: M. Vicen, P. Fabian, J. Bronček, M. Drbúl

The stresses in structural components can appear due to different reasons: loading, manufacturing long-time operations, etc. One of the reasons for stresses appearance is the heat treatment to which components sometimes need to be subjected. Changes in the size and shape of products are manifestations in the heat treatment. Although those changes are undesirable, they cannot be completely avoided and/or eliminated. This article deals with the effect of the heat treatment on change of the size of bearing rings. The aim was to compare the dimensions before and after the heat treatment, to find out whether the changes are within tolerance ranges or if the additional processing of components would be necessary. Another aim was to monitor the effect of layout of bearing rings on dimensions change.

63-71

Authors: I. Sovilj-Nikić, S. Sovilj-Nikić, B. Sovilj, I. Samardžić, D. Kozak, V. Blanuša

The problem of generating is analyzed in science and practice in various ways by identifying it once as an element of the machine, and the second time as a part of production, that is, a final product. The nature of the materials of the machine elements, the loads in the contact zone, the relative velocities, the topography of the contact surfaces, and the temperature in the contact zone influence on the tribological characteristics of the elements, and hence on the characteristics of the tribo-mechanical systems. The surfaces of the tribo-mechanical elements of the machines through which mutual contact is realized are essentially thin layers of materials whose composition and properties differ significantly from the properties of the basic mass element material. There are a significant number of tribo-mechanical systems in the energy sector. Gear cutting is the most important operation in the production of gears. The quality of the gear cutting is one of the conditions for achieving the required quality of the work-piece. The gear is an element of a large number of tribo-mechanical systems. The geometrical parameters of the hob milling, the accuracy of the profiling and the accuracy of manufacture significantly affect the productivity and machining costs. In this paper, the topography and roughness parameters of lateral back surfaces of the model hob milling tools are analyzed before and after cylindrical gear cutting.

78-83

Authors: N. Petrović, N. Kostić, N. Marjanović, V. Marjanović

The use of continuous variables for cross-sectional dimensions in truss structural optimization gives solutions with a large number of different cross sections with specific dimensions which in practice would be expensive, or impossible to create. Even slight variations from optimal sizes can result in unstable structures which do not meet constraint criteria. This paper shows the influence of the use of discrete cross section sizes in optimization and compares results to continuous variable counterparts. In order to achieve the most practically applicable design solutions, Euler buckling dynamic constraints are added to all models. A typical space truss model from literature, which use continuous variables, is compared to the discrete variable models under the same conditions. The example model is optimized for minimal weight using sizing and all possible combinations of shape and topology optimizations with sizing.

1-5

Authors: R. Mitrović, D. Momčilović, I. Atanasovska

Researchers in the field of fracture mechanics, predominantly developing appropriate solution algorithms for problems of solid bodies with cracks. Problems in mechanics generally, related with fracture and fatigue for solid bodies with various geometries of sharp notches, are studied to a much lesser extent. This situation can be explained by analytical difficulties arising in solving problems of elasticity theory for bodies with rounded notches. To solve problems of such class, starting from data on stress concentration in the rounded notch tip with a significant radius of curvature, simplified solutions with are therefore of great importance. Recent years, due to constant rise of computing power and development of numerical methods, re-evaluation of stress concentration factors from a viewpoint of theory of elasticity is present. This is mainly as a feedback from industry, which have requirements toward mega and nanostructures. Corrosion represents an important limitation to the safe and reliable use of many alloys in various industries. Pitting corrosion is a form of serious damage on metals surface such as high-strength aluminum alloys and stainless steel, which are susceptible to pitting when exposed to a corrosive attack in aggressive environments. This is particularly valid for dynamic loaded structures. The basic idea behind this paper is finding links between different scientific and engineering disciplines, which will enable useful level of applicability of existing knowledge. The subject of this paper is application of new method of determine length scale parameter for estimating the mechanistic aspect of corrosion pit under uniaxial/multiaxial high-cycle fatigue loading…

13-19

Authors: S. Dizdar, R. Tomović, A. Vučina

Micro cracks have been found near some of the welds on the pipe unit. This paper investigates the root cause of this damage and suggests improvements to prevent such damage from occurring. The investigation includes several simulations using Pipestress and Ansys Mechanical, a welding and materials investigation, and a more theoretical creep investigation using the Larson-Miller parameter. A sensitivity study of the outlet pigtail installation and support configuration is performed as well as a cyclic plastic analysis. A complementary analysis of the catalyst tubes, inlet and outlet system shows that the only areas where the stress and strain indicate an elevated risk of damage are the areas around the ends of the outlet pigtails. Suggested improvements include reconfiguration and load reduction of constant hanger supports, improving welding procedures in order to lower residual stresses and undertake more material and on site investigations to verify causes of failure.

27-33

Authors: A. Bergant, J. Mazij, U. Karadžić

Hydropower plants play an important role in the growth of the renewable energy sector. The main objective of the paper is to present, discuss and assess critical parameters which may cause unacceptable water hammer loads in hydropower plants. Water hammer is caused by flow disturbances in a conduit from one steady state to another. It induces pressure rise or drop in hydraulic systems, rotational speed variation in hydraulic turbomachinery and level fluctuation in surge tanks and air chambers. Design principles of water hammer control strategies (mitigation of excessive loads) are outlined including operational scenarios (closing and opening laws),surge control devices (flywheel, surge tank, regulating valve, air valve, etc.) or redesign of the pipeline components. Water hammer models and solutions are briefly discussed in the light of their capability. Case studies include hydropower plants with long fluid conveying systems (open channels, tunnels) and water hammer control devices (surge tank, regulating valve).

40-45

Authors: E. Nezirić, S. Isić, E. Džiho

Vibrations are common phenomenon in the rotating machinery, which could carry important information about condition of the rotating machinery. All specific failures in rotating machinery have their own characteristics of the vibrations. By measuring and analysis of vibrations cause of increased vibrations could be determined. Since misalignment and rotating looseness have similar frequency spectrum characteristics, it is difficult to determine which one of the failures is present. When cause of increased vibrations is determined, it is possible to plan the future steps for the repairing and neutralising present cause of the possible failure. Process of vibration analysis followed by present cause of increased vibration in rotating machinery repairing is presented in this paper through example on the ventilation system for smoke drain in the thermal power plant.