1. Effects of fixture configurations and weld strength mismatch on J-integral calculation procedure for SE(B) specimensPrimož Štefane, Stijn Hertelé, Sameera Naib, Wim de Waele, Nenad Gubeljak, 2022, original scientific article Abstract: This work presents the development of a J-integral estimation procedure for deep and
shallow cracked bend specimens based upon plastic ηpl factors for a butt weld made in an S690 QL
high strength low alloyed steel. Experimental procedures include the characterization of average
material properties by tensile testing and evaluation of base and weld metal resistance to stable tearing
by fracture testing of square SE(B) specimens containing a weld centerline notch. J-integral has been
estimated from plastic work using a single specimen approach and the normalization data reduction
technique. A comprehensive parametric finite element study has been conducted to calibrate plastic
factor ηpl and geometry factor λ for various fixture and weld configurations, while a corresponding
plastic factor γpl was computed on the basis of the former two. The modified ηpl and γpl factors were
then incorporated in the J computation procedure given by the ASTM E1820 standard, for evaluation
of the plastic component of J and its corresponding correction due to crack growth, respectively. Two
kinds of J-R curves were computed on the basis of modified and standard ηpl and γpl factors, where
the latter are given by ASTM E1820. A comparison of produced J-R curves for the base material
revealed that variations in specimen fixtures can lead to ≈10% overestimation of computed fracture
toughness JIc. Furthermore, a comparison of J-R curves for overmatched single-material idealized
welds revealed that the application of standard ηpl and γpl factors can lead to the overestimation of
computed fracture toughness JIc by more than 10%. Similar observations are made for undermatched
single material idealized welds, where fracture toughness JIc is overestimated by ≈5%.
Keywords: metal weld, strength mismatch, fracture, plastic correction factors, fixture rollers, J-R resistance curve
Published in DKUM: 20.03.2025; Views: 0; Downloads: 3
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2. Application of normalization method to fracture toughness testing of welds with pronounced strength heterogeneity : doctoral disertationPrimož Štefane, 2022, doctoral dissertation Abstract: This doctoral dissertation presents the results of an extensive fracture testing programme of
welds with pronounced strength heterogeneity. Purpose of this programme was to determine
fracture toughness of heterogeneous welds that contain a midplane crack. Application of
standardized fracture testing methods in heterogeneous welds might lead to overestimation or
underestimation of fracture toughness and consequentially to inaccurate assessment of
structural integrity. Reasons for that are variations in mechanical properties of different
material regions in the weld which have a significant impact on development of deformation at
the crack tip, and consequently on the crack driving force. Experimental procedures in scope
of this research include fabrication of weld sample plates, that were welded with MAG process.
The welds were fabricated using two different electrodes, one with higher and one with lower
mechanical properties, with respect to base material S690QL in order to replicate extreme
variations of mechanical properties in the weldment. Fabricated welds were then characterized
in detail using metallography, three-point bend impact testing, indentation hardness
measurements and tensile testing of flat miniature and round bar standard tensile specimens.
Resistance of welds to stable tearing was investigated by fracture testing of square surface
cracked SE(B) specimens containing a weld midplane notch. J-integral has been estimated from
plastic work, using the normalization data reduction method that is included in standard ASTM
E1820. The advantage of the normalization data reduction method is that no special equipment
or complex testing method is needed to measure ductile crack growth during fracture testing.
The ductile crack growth is determined directly from the load-displacement record, by applying
appropriate calibration function and physical lengths of initial and final cracks that were
measured post-mortem with the nine-point method. Several correction factors had to be
calibrated in order to successfully implement the normalization data reduction method to
fracture testing of welds with pronounced strength heterogeneity. For that reason, parametric
finite element analyses were conducted for several weld configurations. Finite element models
incorporated plane strain conditions in order to provide calibrated factors that comply with
plane strain equations included in ASTM E1820. Additionally, crack tip constraint has been
extensively analysed and correlated with the plastic deformation fields. This clarified altered
deformation behaviour of modelled welds in comparison with the base material and
corresponding effect on fracture toughness. Finally, calibrated factors were applied to
computation of J-integral from data that were measured during fracture testing. J-R resistance
curves were constructed for the tested heterogeneous welds and compared to the ones of the
base material. This directly showed the effect of variations of mechanical properties on the
weld fracture behaviour.
Keywords: weld, strength mismatch, fracture, normalization data reduction technique, plastic
correction factors, test fixture, SE(B) specimen, J-R resistance curve
Published in DKUM: 10.01.2023; Views: 778; Downloads: 207
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3. Razvoj in dimenzioniranje naprave za cepljenje drv : diplomsko deloJaka Bezjak, 2021, undergraduate thesis Abstract: V diplomski nalogi je opisan postopek konstruiranja cepilne naprave. Opisani so koraki pregleda trga, izdelave zahtevnika, funkcijske strukture ter iskanje in vrednotenje rešitev. Na podlagi najdenih rešitev so dimenzionirane komponente naprave, kot so hidravlični cilinder, naležna plošča ter sorniki in vijaki. Pri tem je bil uporabljen programski paket SolidWorks, v katerem so bile vse komponente sproti zmodelirane. Postopek je izveden za cepilnik in klešče posebej. Na koncu je bila CAD geometrija analizirana po metodi končnih elementov v programskem paketu PrePoMax. Ustrezni konstrukcijski popravki pa so bili izvedeni na osnovi dobljenih numeričnih rezultatov.
Keywords: razvoj, konstruiranje, cepilec za les, CAD, MKE
Published in DKUM: 24.09.2021; Views: 959; Downloads: 151
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4. Simuliranje duktilnega loma s pomočjo GTN mikromehanskega poškodbenega modela : magistrsko deloFilip Jerenec, 2020, master's thesis Abstract: V magistrski nalogi je obravanavano mikromehansko modeliranje duktilnega loma z uporabo Gurson-Tvergaard-Needleman mikromehanskega poškodbenega materialnega modela (GTN), z namenom ugotavljanja primernosti tega modela za numerično določanje lomnomehanskih lastnosti obravnavanega materiala, na podlagi SE(B)-preizkušancev. Zraven mikromehani-zmov duktilnega loma je predstavljen tudi zgodovinski razvoj (v modernejši Kompletni Gurso-nov model - CGM), je hkrati poenostavljeno predstavljena njegova matematična sestava in delovanje. Prikazana je kalibracija CGM, ki je bila izvedena z uporabo parametričnih nume-ričnih simulacij in je temeljila na eksperimentalnih rezultatih standardnih in nestandardnih na-teznih preizkusov. Nazadnje so prikazani še izdelava numeričnega modela obravnavanih SE(B)-preizkušancev (z implementacijo kalibriranega CGM-modela) ter rezultati numerične simulacije, na podlagi katerih je bilo določeno, da model je primeren za numerično določanje lomnomehanskih lastnosti obravnavanega materiala na podlagi SE(B)-preizkušancev
Keywords: duktilni lom, mikromehansko modeliranje, Kompletni Gursonov model, CGM, Gurson-Tvergaard-Needleman, GTN
Published in DKUM: 12.01.2021; Views: 877; Downloads: 155
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5. Dimenzioniranje in razvoj nosilca dodatne opreme pečice : diplomsko deloIgor Vuković, 2019, undergraduate thesis Abstract: Razvitost trga vsak dan postaja vse večja, kupci postajajo zahtevnejši, podjetja se morajo prilagoditi zahtevam kupca, da bi obdržala promet in ostala na trgu.
V podjetju Gorenje d.o.o. se je s prihodom nove generacije visoko-cenovnega razreda kuhalnih aparatov pojavila potreba po razvoju nečesa inovativnega, ker se od teh pečic pričakuje popolnost v vsakem pogledu. Predmet diplomskega dela je razvoj nosilca dodatne opreme zaradi lažjega obratovanja s številnimi pekači, ki so osnovni del vsake pečice.
Nosilec moramo sprva skonstruirati, nato izvesti statično analizo in na koncu izdelati prototip, da se prepričamo, da je vse tako, kot mora biti. Z razvojem takšnega nosilca želimo uporabniku poenostaviti in pohitriti vsakodnevno uporabo pečice »Life simplified«.
Keywords: vgradne pečice Gorenje, dodatna oprema, pekači, razvoj
Published in DKUM: 18.10.2019; Views: 1251; Downloads: 87
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6. Characterization of heterogeneous arc welds through miniature tensile testing and Vickers-hardness mappingStijn Hertelé, Jonas Bally, Nenad Gubeljak, Primož Štefane, Patricia Verleysen, Wim de Waele, 2016, original scientific article Abstract: The heterogeneity of arc-welded connections is often ignored in structural assessments, giving rise to inaccuracies. Improved assessments taking into account heterogeneity require the characterization of local constitutive properties. We have compared two methods to do this: Vickers-hardness mapping and miniature tensile testing. Whereas the former is more straightforward to apply, the latter provides full-range stress-strain data. This paper discusses an experimental comparison of both methods on a heterogeneous arc weld. Miniature tensile tests were performed, using digital image correlation to measure the strain. The specimens were indented to compare their stress-strain response with Vickers hardness. Notwithstanding that small natural flaws invalidated some tests, reliable stress-strain curves were obtained. Vickers hardness testing is a convenient alternative if the yield and ultimate tensile strength are the only points of interest and the corresponding conversion inaccuracy is acceptable.
Keywords: arc weld, heterogeneity, hardness, miniature tensile testing, digital image correlation
Published in DKUM: 14.03.2017; Views: 1364; Downloads: 453
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7. Lomno obnašanje konstrukcijskega jekla v temperaturno prehodnem območjuPrimož Štefane, 2014, master's thesis Abstract: Vsebina magistrske naloge opisuje lomno obnašanje konstrukcijskih jekel v odvisnosti od temperature v temperaturno prehodnem območju. Izrazit raztros, ki ga konstrukcijska jekla kažejo v temperaturno prehodnem območju, je posledica vpliva napetostnega oz. deformacijskega stanja na mikrostrukturo jekla oz. na vsebino krhkih območij (vključkov, izločkov ali napak v materialu). Parameter m, ki definira razmerje med CTODel in Jel v odvisnosti od napetostno- deformacijskega stanja na konici razpoke, se spreminja glede na delež ravninsko deformacijskega stanja (RDS) in ravninsko napetostnega stanja (RNS) skozi temperaturno prehodno področje. V okviru naloge bo določena odvisnost med parametrom m in lomnim obnašanjem konstrukcijskih jekel skozi temperaturno prehodno področje.
Keywords: feritno jeklo, temperaturno prehodno območje, lomna žilavost, mehanika loma
Published in DKUM: 29.10.2014; Views: 2038; Downloads: 342
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8. Določitev preizkuševalne obremenitve za os veterne elektrarnePrimož Štefane, 2012, undergraduate thesis Abstract: Vsebina diplomske naloge opisuje konstrukcijo vetrnih elektrarn. Podrobna obravnava se nanaša na os vetrne elektrarne z direktnim pogonom, obremenitve na os, ki so posledica delovanja vetra, in lastnosti materiala osi. Cilj naloge je kontrola osi na ekstremne obremenitve in življenjsko dobo ter določitev primerjalne obremenitve, ki jo simuliramo pri izvajanju materialnega preizkusa. Pri reševanju problema upoštevamo standarde s tehničnega področja.
Keywords: vetrna turbina, vetrna energija, os elise, obratovalna trdnost, obremenitveni spekter
Published in DKUM: 20.11.2012; Views: 2244; Downloads: 312
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