RMZ â MATERIALI IN GEOOKOLJE

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342 Kugler, G., Terčelj, M., Peruš, I., Turk, R.Figure 6. Comparison of dependence of minimal radius of deformed rod on elongationcalculated by models for catenary, cylinder, and for assumption of homogeneous deformationfor ε = 0.1 s –1 at T = 1000 °C (a), and T = 900 °C (b). Evolution of the radius of.the circle osculating the profile at the neck, R B, and corresponding dependence of Bridgmancorrection coefficient, k B, on elongation calculated by catenary model at T = 1000°C (c), and T = 900 °C (d).Figure 7. Comparison of dependence of minimal radiuses on elongation between measurementsconducted by digital camera and calculated by studied models (catenary, cylinder,homogeneous deformation) for ε = 0.1 s –1 at T = 950 °C (a), and at T = 900 °C (b)..<strong>RMZ</strong>-M&G 2012, 59
Calculation of stress-strain dependence from tensile tests at high temperatures using ...343For comparison the minimal radiusescalculated by cylindrical model and byassumption of homogeneous deformationare also given. It can be seen thatthe radius obtained by cylindrical modelis very close to one obtained by catenary,whereas as expected the radiusaccording to homogenous deformationmodel after occurrence of necking startdo deviate from values predicted by ourmodels. Deformation is homogeneousapproximately up to elongation of 2mm that corresponds to strain ≈0.2. Asit was already mentioned, the transitionfrom homogeneous to nonhomogeneousdeformation leads to transition ofuniaxial to three-axial stress state. Forcalculation of Bridgman correction, k B,the radius of the circle osculating theprofile at the neck, R B, is needed. TheR Bis calculated by equation (10) fromreconstructed contours. The evolutionof R Band k Bare given on Figure 6c,and 6d, respectively. When the contoursare calculated by the homogeneousdeformation model, we set k B≡ 1,consequently the dependence of k B(Δl)is discontinued at transition betweenboth areas, with negligible error.Calculated values of the time evolutionof the minimal radius of the tensilespecimens were compared withthe values obtained from analysis ofthe pictures which were recorded bya digital camera, and we obtained reasonableagreement. These results areshown on Figure 7, were the maximalestimated errors for minimal radiusmeasured with camera are denoted.Due to intensive radiation from hotsamples, the sharp boundary betweenthe rod and surrounding was indistinct,thus the determination of real minimalradius was hindered.True stress–true strain curvesFrom technical force-elongationcurves the true stress–true strain curveswere determined by employing all theprocedures explained in previous sections.They are shown on Figures 8a–c,whereas Figures 8d–e show the actualvariation of strain rates during the tests.For higher temperatures and/or lowerstrain rates the flow stress initiallyraises until a maximum is reachedwhen hardening and softening are inbalance. With increasing deformation,softening prevails over hardening andflow stress decreases. At strains ε >0.2 flow stress starts to increase andincreases until the end of the experiment.This kind of behaviour in thelater stages of deformation is a consequenceof the continuously increasingstrain rate after the appearanceof necking. For the same reason flowcurves for low temperatures and/orhigher strain rates do not reach a maximum.Thus, we can conclude thatafter necking, the stress-strain curvesare not flow curves as by definitionflow curves are stress-strain curves atconstant temperature and strain rate.<strong>RMZ</strong>-M&G 2012, 59
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392 Shemetov, P. A., Bibik, I. P.in
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394 Shemetov, P. A., Bibik, I. P.
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398 Shemetov, P. A., Bibik, I. P.si
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434 Kos, A., Dervarič, E.chines to
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436 Kos, A., Dervarič, E.the best
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438 Kos, A., Dervarič, E.Before th
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440 Kos, A., Dervarič, E.nally to
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444 Lajovic, A.disc brakes, further
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446 Lajovic, A.Slika 2. Izrez iz Si
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448 Lajovic, A.Livne lonce smo na n
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450 Lajovic, A.Ingersol pa je bil z
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452 Lajovic, A.Med delavci, ki so b
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454 Lajovic, A.imel vsak delavec na
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456 Lajovic, A.Slika 5. Izdelki Že
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458 Lajovic, A.pa se ni najbolje iz
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460 Lajovic, A.za delo. Promet na z
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462 Lajovic, A.Sredi osemdesetih le
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464 Lajovic, A.njem delu forme. Na
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466 Lajovic, A.Enourni film je mars
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470 Medved, J., Rosina, A., Vončin
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472 Author’s IndexAuthor`s Index,
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Contents476Phase contrast method fo
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Contents47859/4Calculation of stres
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Instructions to authors481Compositi
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Instructions to authors483NAVODILA
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Instructions to authors485Knjige:Ro
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Template487TEMPLATEThe title of the
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