168 research outputs found
Procena preostale čvrstoće metodom konačnih elemenata korozijom oštećenih čeličnih cevovoda u Hemijskoj industriji
Ovaj rad koristi napredne tehnike modeliranja korodiranih površina cevovoda, bazirane na Metodi
konačnih elemenata (MKE), sa ciljem razvoja procedure za procenu preostale čvrstoće čeličnih
cevovoda koji rade u uslovima sredine industrije hemijskih proizvoda.
U radu je dat i prikaz mogućih oštećenja i posledica izazvanih korozijom čeličnih cevovoda u
industriji hemijskih proizvoda, a razmotrena je i mogućnost preduzimanja mera da se takve pojave
preventivno spreče
Low cycle fatigue of high strength low alloy steels
Imajući u vidu heterogenost svojstava zavarenog spoja, a naročito uske zone pod
uticajem toplote, u ovoj disertaciji je eksperimentalno ispitivano i analizirano ponašanje
niskolegiranog čelika povišene čvrstoće (HSLA) u uslovima niskocikličnog zamora, na
glatkim okruglim epruvetama iz osnovnog metala i epruvetama dobijenim termičkom
simulacijom zone pod uticajem toplote. Takođe je ispitivano ponašanje osnovnog
metala i simulirane zone pod uticajem toplote u uslovima dejstva kavitacije.
Čelik, Nionikral 70 (NN-70), odabran u ovoj disertaciji za istraživanje ponašanja
pri zamornom opterećenju i dejstvu kavitacije, spada u grupu niskolegiranih čelika
povišene čvrstoće koji se, između ostalog, primenjuju u brodogradnji kao i za izradu
posuda pod pritiskom.
Ciljevi istraživanja su da se, u odsustvu pouzdanijih teorija o zamaranju i
kavitaciji, pogodnom metodom ispitivanja, tj. simuliranjem strukture materijala i dejstva
opterećenja odnosno deformacija, u laboratorijskim uslovima na odgovarajućim
uzorcima - epruvetama, dođe do rezultata koji su posredno ili neposredno primenljivi u
proračunima i da se dobijeni rezultati eventualno iskoriste i za fundamentalna
proučavanja tokova procesa zamaranja i kavitacije kako osnovnog metala, tako i zone
uticaja toplote zavarenih spojeva.In this dissertation the experimentally investigated and analyzed behavior of a
low-alloyed high strength steel exposed to the low cycle fatigue is done. Taking into
account the welded joint properties heterogeneity, especially its narrow heat-affected
zone, experiments were performed on two kinds of specimens: smooth round specimens
made of parent material (PM) and specimens obtained by thermal simulation of the
heat-affected zone (SHAZ). The behavior of PM and SHAZ affected by cavitation were
also investigated.
Steel designated as Nionicral 70 (NN-70), selected in this dissertation to
investigate the behavior of fatigue and cavitations’ loads, belongs to a group of lowalloy steels of high strength, which are, among other things, applied in shipbuilding as
well as for the production of pressure vessels.
The research aims are that, in the absence of more reliable theories of fatigue
and cavitation, a suitable test method, i.e. simulating the structure of the material and
the load and/or deformation in laboratory conditions on the appropriate specimens,
results are obtained which are directly or indirectly applicable in the calculations, and
that the obtained results are possibly used for the fundamental study of the fatigue and
cavitation processes of the parent material, as well as its heat-affected zone in welded
joints
Presence of crack due the constant exploitation of turbine shaft
Designing, constructing and putting into operation a hydroelectric power plant includes complex
tasks. Stresses of turbine and hydromechanical equipment of hydro power plants arise during the
production of parts and assembly of equipment (residual stresses), in the process of performing
functional requirements in exploitation and in the disturbed process of exploitation.
After several decades of constant exploitation of the horizontal bulb turbine, which is an integral
part of the hydroelectric power unit, empirically, the formation of a crack occurs in the turbine
shaft due to the influence of corrosion, erosion and cavitation.
Through experimental tests and calculations it has been determined that values of bending stresses
of the turbine, which occur due to the action of fatigue and corrosion, as well as stress
concentration, are bigger than 25 MPa for flanges exposed to water, and in other case bigger than
40 MPa for flanges exposed to `corrosive water` and can cause the occurrence of surface cracks
on the transition radius between the cylindrical part of the shaft and the flange. It has been
determined that stress values in the zone under the influence of bending stresses were bigger than
allowable values, which led to the occurrence of many cracks due to fatigue corrosion. One of
those cracks caused the failure of the shaft and of the whole turbine
Methodology for determining the region of stabilization of low-cycle fatigue
In present paper, the behaviour of high-strength low-alloyed (HSLA) steel under conditions
of low-cycle fatigue (LCF) has been experimentally tested and analyzed. Based on the experimental
results obtained in the programme EXCEL, characteristic regions of low-cycle
fatigue of steel NIONIKRAL 70 (NN-70) have been determined, the most important being
the region of stable behaviour of materials, so-called "the region of stabilization". From this
region, on the basis of pre-defined requirements, characteristic stabilized hysteresis have
been isolated for each strain level, based on which the Indicators of low-cycle fatigue of
steel NN-70 have been identified
Metodologija određivanja pokazatelja ponašanja HSLA čelika pri delovanju niskocikličnog zamora
U radu je analizirano eksperimentalno istraživanje ponašanja niskolegiranog čelika povišene
čvrstoće (HSLA) u uslovima niskocikličnog zamora (LCF), sa kontrolisanom i potpuno
reverzibilnom deformacijom (/2 = const, R = min/max = -1). Ispitivanja niskocikličnog
zamora obavljena su na seriji glatkih epruveta od čelika Nionikral 70 (NN-70), sa
poluamplitudom kontrolisane deformacije, /2=0.35, 0.45, 0.50, 0.60, 0.70 i 0.80. Za izbor
stabilizovanih histereza i obradu rezultata ispitivanja niskocikličnim zamorom, korišćene su
preporuke standarda ISO 12106:2003 (E) i ASTM E 606-04, kao i dve nove metode: Metoda
sredine stabilizacije (MSS) i Metoda praga NDT (MpNDT), što u ovom radu predstavlja četiri
rezultata za poređenje. Za svaki nivo deformacije izabrane su karakteristične stabilizovane
histereze, određene prema preporuci standarda ISO 12106:2003 (E) i ASTM E 606-04, MSS i
MpNDT, sa kojih su očitani potrebni podaci za dalju obradu rezultata i konačno, konstruisanje
karakterističnih krivih niskocikličnog zamora. Konstruisane krive su međusobno poređene, a
ocenjen je uticaj izbora karakterističnih stabilizovanih histereza na karakterizaciju ponašanja
čelika NN-70. Rezultati eksperimentalnih ispitivanja su nam dali važne podatke o razumevanju
zamornog ponašanja čelika NN-70. U radu je izvršeno i poređenje rezultata statičkog i
dinamičkog, odnosno monotonog i zamornog ponašanja materijala, što predstavlja praktični
doprinos oceni ponašanja čelika NN-70 u uslovima delovanja niskocikličnog zamora
Analiza opravdanosti modeliranja sučeono zavarenih spojeva kod proračuna posuda pod pritiskom
U radu je posle proračuna metodom konačnih elemenata (MKE) analizirana raspodela napona
na modelu dela oplate rezervoara pod pritiskom bez zavarenih spojeva (ZS), sa obimnim ZS,
podužnim ZS i ukrsnim mestom ZS. Takođe, u radu je na primeru rezervoara za tečni ugljendioksid,
na kome su pored limova oplate i danaca sa potrebnim otvorima i elementima kao što su
sedla sa osloncima i uške modelirani obimni i podužni sučeoni ZS, urađen proračun MKE i
uporedna analiza uticaja ZS na raspodelu napona
Finite element method pressure vessel calculation and analysis of the effects of the butt welded joints on a carrying capacity of a structure
In present paper, after calculation using the finite element method (FEM), stress distribution
on the model of a part of the pressurized boiler shell without welded joints (WJ), with transversal
WJ, longitudinal WJ and crosspoint location of WJ Is analyzed. Also, FEM calculation
and comparative analysis of the effects of WJ on the stress distribution have been conducted
using the tank for liquid carbon dioxide as an example, on which. In addition to the
shell sheet-metal and heads with necessary openings and elements such as saddles with supports
and hangers, transversa! and longitudinal butt WJ, have been modelled
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