Determination of critical size of corrosion pit on mechanical elements in hydro power plants

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…

A new methodology for prediction of high-cycle contact fatigue for spur gears

High-cycle contact fatigue is a localized phenomenon that occurs in highly stressed grains of the material on or under the contact region. The contact zones of tooth flanks for meshed gears are subjected to contact fatigue damages that causes pitting and leads to gears failure. The objective of this paper is to give a new viewpoint in contact fatigue prediction in the case of high-cycle fatigue. The main aim of the presented research is to make the methodology for direct calculation of fatigue crack initiation in contact zones. This methodology is developed for spur gears and used up-to-date methods and multidisciplinary approach. Two methods are built in the new methodology: the Theory of Critical Distances (TCD) and the Finite Element Method (FEM). In this paper the comparative analysis of standard and new methodology for prediction of fatigue crack initiation on tooth flanks is presented. The advantages of methods and procedures used in the new methodology are presented through a case study of particular gear pair. The Finite Element Analysis on 3D gear contact model is used for stress and strain calculation and prediction of the maximum stress location in contact zones along the gear face width. The stress gradient curves from the contact zone are made for a pinion tooth in different cross sections along gear facewidth. The Theory of Critical Distances used these stress gradients and material characteristics for fatigue crack initiation prediction. The benefits of presented methodology are shown by the detail analysis of the obtained results

A new methodology for prediction of high-cycle contact fatigue for spur gears

High-cycle contact fatigue is a localized phenomenon that occurs in highly stressed grains of the material on or under the contact region. The contact zones of tooth flanks for meshed gears are subjected to contact fatigue damages that causes pitting and leads to gears failure. The objective of this paper is to give a new viewpoint in contact fatigue prediction in the case of high-cycle fatigue. The main aim of the presented research is to make the methodology for direct calculation of fatigue crack initiation in contact zones. This methodology is developed for spur gears and used up-to-date methods and multidisciplinary approach. Two methods are built in the new methodology: the Theory of Critical Distances (TCD) and the Finite Element Method (FEM). In this paper the comparative analysis of standard and new methodology for prediction of fatigue crack initiation on tooth flanks is presented. The advantages of methods and procedures used in the new methodology are presented through a case study of particular gear pair. The Finite Element Analysis on 3D gear contact model is used for stress and strain calculation and prediction of the maximum stress location in contact zones along the gear face width. The stress gradient curves from the contact zone are made for a pinion tooth in different cross sections along gear facewidth. The Theory of Critical Distances used these stress gradients and material characteristics for fatigue crack initiation prediction. The benefits of presented methodology are shown by the detail analysis of the obtained results

Methodology of determination the influence of corrosion pit on decrease of hydro turbine shaft fatigue life

This paper describes the influence of corrosion on stress concentration factor and crack initiation at shaft flange transition section. The case study of hydraulic turbine shaft failure is used as the basis for this research. The quantification of the stress concentrators was accomplished by the usage of Theory of critical distances (TCD) in the prediction of high-cycle fatigue behavior in machine parts and systems. The stresses obtained by Finite Element Analysis, was used as an entry values for application of Theory of critical distances. The TCD represents a major extension of linear elastic fracture mechanics, allowing it to be used for short cracks as well as for stress concentrations of arbitrary geometry. Presented methodology is particular valid for machine parts of non-standard dimensions. The significance of results presented in this paper is that TCD and developed methodology can be used in preventing failures in power industry

Combined load simulation vs component loads simulation in machine design: A case study

Na sadašnjem nivou razvoja tehnologije, u stvarnim radnim uslovima, gotovo svi mašinski elementi su opterećeni kombinovanim opterećenjima. Cilj istraživanja prikazanog u ovom radu je ukazivanje na značaj proračuna nosivosti mašinskih elemenata simuliranjem kombinovanog opterećenja. Istraživanje prikazano u radu inspirisano je jednim stvarnim otkazom turbinskog vratila hidroturbine. Vratilo sa prirubnicom i visokim odnosom prečnika vratila i prirubnice bilo je predmet obimnih proračuna u cilju pronalaženja uzroka otkaza. Klasični analitički proračun ovog vratila koristi Peterson-ov faktor koncentracije napona i proračun maksimalnih napona za pojedine naponske komponente kombinovanog opterećenja, a onda analitičku vrednost ukupnog napona proračunava na osnovu hipoteze o maksimalnom normalnom naponu. Sa druge strane, prikazani proračun naponskog stanja vratila metodom konačnih elemenata bazira se na simuliranju realnih radnih opterećenja u uslovima kombinovanog opterećenja istovremenim definisanjem svih komponenti (savijanja, uvijanja i zatezanja). Oba proračuna urađena su za nekoliko različitih radijusa na prelazu vratila ka prirubnici. Dobijeni rezultati prikazani su uporednim dijagramima dobijenih vrednosti ukupnih napona i odgovarajućih faktora koncentracije napona. Analiza ovih dijagrama vodi do zaključka da proračun ukupnog napona u slučaju kombinovanog i složenog opterećenja na bazi Peterson-ovih faktora koncentracije napona i standardnog analitičkog postupka treba da bude zamenjen naprednim tehnikama proračuna koji obezbeđuju tačnija rešenja koja se istovremeno i jednostavnije analiziraju i koriste.At a present level of technology, almost all machine parts are subjected to combined loads in real working condition. The aim of research described in this paper is to highlight the importance of combined load simulation for the calculation of machine parts load capacity. This research is inspired by one failure case study of hydro turbine shaft. The shaft with flange and high ratio of shaft/flange diameter is the subject of excessive calculation in order to find the cause of failure. The classic analytical calculation of this shaft uses the Peterson's elastic stress concentration factor and calculates stress concentration factors and maximum stresses for different stress components of combined load and then calculate analytical values of total stress by the hypothesis of maximum normal stress. On the other hand, presented Finite Element Analysis simulates shaft stress state under real conditions of complex load by simultaneously applying all load components (bending, torsion and tension). Both of the calculations are performed for few different radii in shaft-flange sections. The results are presented by comparative diagrams for obtained values of total stresses and stress concentration factors. The analysis of these diagrams leads to conclusion that the use of Peterson's stress concentration factors and standard analytical techniques for total stress calculation has to be replaced with modern calculation techniques that provide a more accurate, easier-to-handle solution

Methodology of determination the influence of corrosion pit on decrease of hydro turbine shaft fatigue life

This paper describes the influence of corrosion on stress concentration factor and crack initiation at shaft flange transition section. The case study of hydraulic turbine shaft failure is used as the basis for this research. The quantification of the stress concentrators was accomplished by the usage of Theory of critical distances (TCD) in the prediction of high-cycle fatigue behavior in machine parts and systems. The stresses obtained by Finite Element Analysis, was used as an entry values for application of Theory of critical distances. The TCD represents a major extension of linear elastic fracture mechanics, allowing it to be used for short cracks as well as for stress concentrations of arbitrary geometry. Presented methodology is particular valid for machine parts of non-standard dimensions. The significance of results presented in this paper is that TCD and developed methodology can be used in preventing failures in power industry

Effects of operation temperature on thermal expansion and main parameters of radial ball bearings

The research of influence of operation temperature on the thermal expansion and main parameters of radial ball bearings is presented in this paper. The main bearing parameters are identified in accordance with the increasing requests concerning stability and load capacity. A series of finite element analyses is performed for quasi-static analysis of all identified bearing parameters during contact period in referent temperature. Then, the dependence of bearing material characteristics on the operation temperature is discussed. Few series of finite element analyses are performed for a particular radial ball bearing type, with characteristics in accordance with manufacturer specifications, for several operation temperatures. These two problems analyses include consideration of relation between the initial radial clearance, thermal expansion strains, and contact deformations of the parts of the bearing assembly. The results for radial ball bearing parameters are monitored during a ball contact period for different temperatures and the appropriate discussion and conclusions are given. The conclusions about the contribution of developed procedure in defining the optimum operation temperature range are shown

Service life prediction of running steel wire ropes

Vrlo visoka čvrstoća omogućava žičanom užetu da prenese velike zatezne sile i da se kreće po koturima relativno malog prečnika. Žice od čelika vrlo visoke čvrstoće su postojale više od sto godina pre nego što su patentirane, kada je uveden specijalni postupak zagrevanja i usavršen postupak izvlačenja. Dalja poboljšanja posle toga su uvedena u relativno malim koracima. Žičana užad uvek imaju ograničen radni vek. Zbog toga ona moraju da se podvrgnu inspekciji i ispitaju u pravilnim intervalima da bi se zamenila znatno pre otkaza. Krajnji korisnik mašine sa čeličnim žičanim užetom u svakom slučaju želi da ima grubu ocenu radnog veka užeta već u ranoj fazi razvoja mašine. tako da bude u mogućnosti, ako zatreba, da poboljša sistem mašine. To je jedan od razloga zbog kojih su tokom niza godina izvedena obimna istraživanja kako bi se poboljšali postupci proračuna za predviđanje radnog veka žičanih užadi. Namena ovog rada je da ponudi pregled informacija o postupcima proračuna i da prikaže mogućnosti i ograničenja postupaka prognoziranja za predviđanja radnog veka čeličnih žičanih užadi u eksploataciji.Very high strength enables wire ropes to support large tensile forces and to run over sheaves with relative small diameters. Very high strength steel wires had already been in existence for more than a hundred years when patenting, a special heating process was introduced and the drawing process improved. Since then, further improvements have only occurred in relatively small steps. Wire ropes always have a limited service life. Therefore they must be inspected and examined at regular intervals so that they are replaced well before failure. End-users of machinery with steel wire ropes, however, would like to have a rough estimation of the service life of the ropes already in the early stages of conceiving their machines, so that they can, if necessary, improve the revving system. This is one of the reasons why for many years extensive research is carried out in order to improve calculations for predicting the service life of wire ropes. This paper is meant to offer an overview information on the method of calculation and to demonstrate the potential and limitations of the forecasting procedure for service-life prediction of running steel wire ropes

DETERMINATION OF CRITICAL SIZE OF CORROSION PIT ON MECHANICAL ELEMENTS IN HYDRO POWER PLANTS

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 loadin

Morphological characteristics of the lip grooves in citizens of the Republic of North Macedonia determined by Cheiloscopy

Introduction: Cheiloscopy is defined as the study of the sulci labiorum, known as "lip prints". Aim of the study: The aim of this study was to determine the morphological characteristics of the lip grooves in the three dominant nationalities in the Republic of North Macedonia (Macedonians, Albanians, Roma) and to compare the obtained results with the morphological characteristics of the lip grooves in three other populations from different geographical regions. Material and methods: In this research, we included 150 examinees aged 25-50 years and divided them into three groups: Macedonians (50), Albanians (50) and Roma (50). The lip prints were taken using microscopic slides and detected using the dactyloscopic powder and brush method. We used the Suzuki and Tsuchihashi classification to typify the lip prints. Results: The most common type of lip grooves in the population of the Republic of North Macedonia was the type II grooves. There was no significant difference in the presence of different types of lip grooves in the four quadrants between males and females, nor between Macedonians, Albanians and Roma. The comparative analysis showed that populations from different geographical areas had different anthropological and morphological characteristics of the lip grooves. Conclusion: Type II lip grooves are the most common in the population of the Republic of North Macedonia and there is no statistically significant difference between the prevalence of different types of lip grooves in the three nationalities in this study. Considering the large number of factors that can affect the quality of the lip print, we recommend that a swab should always be taken before collecting the lip print in order to attempt to extract DNA material from the found trace