Applied Engineering Letters

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.