At&ra&--Tlx ascetic &f&nation behavior of 0.9999 cu is investi~t~ at strain rates from IO-' to IO4 s-l. The variations of the flow stress and of the mechanical threshold stress (the flow stress at 0 K), which is used as an internal state variable, with strain rate and strain are measured. The experimental results are analyzed using a model proposed by Kocks and Making: results at constant structure are described with thermal activation theory; structure evolution (strain and strain rate evolution of the mechanical threshold stress) is treated by the sum of dislocation generation and dynamic recovery processes. A significant result is that the athermal dislocation accumulation rate, or Stage II hardening rate, becomes a strong function of strain rate at strain rates exceeding IO's_'. This leads to the apparent increased strain rate sensitivity seen in a plot of flow stress at a given strain vs the logarithm of strain rate. An explanation is proposed for the strain rate dependence of this initial strain hardening rate based on the limiting dislocation velocity and average distance between Obstacles.R&urn&--Nous Ctudions la deformation de symetrie axiale dun cuivre 4N pour de-s vitesses de deformation allant de lO-4 s-I a IO's_'. En fonction de la vitesse de deformation et de la deformation, nous mesurons Ies variations de la contrainte d%coulement et de la'&ntrainte seuil mbanique (la contrainte d'6coulement a OK) que l'on utilise comme variable d'etat inteme. Nous analysons les resultats expirimentaux a I'aide d'un modele propose par Kocks et Mecking: les resuhats P structure constante sont d&its par une theorie d'activation thermique; l'tvolution de la structure (evolution du seuil de contrainte m&anique en fonction de la deformation et de la vitesse de deformation) est trait&. par la combinaison des m&canismes de creation des dislocations et de restauration dynamique. Un r&n&at important est I soulingner: la vitesse ~a~umulation athermique des dislocations, ou vitesse de consolidation du stade II, commence ii d&per&e fortement de la vitesse de deformation pour des vitesses de deformation sup&ieures a IO3 s-l. Qci conduit a l'influence apparente accrue de la vitesse de deformation que t'on observe sur les courbes de la contrainte d%couIement a deformation don&e en fonction du Iogarithme de la vitesse de deformation. Nous proposons une explication de l'influence de la vitesse de deformation sur la vitesse de consolidation initiale, explication fond& sur la vitesse Iimite des dislocations et la distance moyenne entre les obstacles,
The true stress-strain curves of polycrystalline aluminum, copper, and stainless steel are shown to be adequately represented by an exponential approach to a saturation stress over a significant range. This empirical law, which was first proposed by Voce, is expanded to describe the temperature and strain-rate dependence, and is put on a physical foundation in the framework of dislocation storage and dynamic recovery rates. The formalism can be applied to the steady-state limit of creep in the same range of temperatures and strain rates; the stress exponent of the creep rate must, as a consequence, be strongly temperature dependent, the activation energy weakly stress dependent. Near half the melting temperature, where available work-hardening data and available creep data overlap, they match. Extrapolation of the proposed law to higher temperatures suggests that no new mechanisms may be necessary to describe high-temperature creep. A new differential equation for transient creep also follows from the empirical work-hardening law.
AIwlraet--In many polycrystals of less than cubic crystal symmetry, plastic deformation is dominated by twinning. In particular, we will treat the case of Zr and Zr alloys in detail. We propose a new method for modelling grain reorientation due to twinning, which is based on a Volume Fraction Transfer (VFT) scheme; the scheme is also applied to the slip modes. We find that this method predicts textures that are, when twinning is the dominant mode, considerably different from, and in better agreement with experiment than the conventional schemes which reorient an entire grain when some criterion has been met. Various combinations of slip and twinning modes and of the associated critical stresses are systematically investigated for the case of rolling, tension and compression of Zr alloys. A comparison of various predicted and experimental textures leads to the conclusion that twinning must, indeed, be controlling texture development.R/~t---Dans de nombreux polycristaux ayant une sym6trie inf6rieure a la sym6trie cubique, la dfformation plastique est domin6e par le maclage. En particulier, nous traitons en d6tail le cas du zirconium et des alliages de zirconium. Nous proposons une nouvelle m6thode pour mod61iser la r6orientation des grains due au maclage, m6thode qui est bas6e sur le concept de transfert de la fraction volumique (TFV); la m~thode est aussi appliqu6e aux modes de glissement. Nous trouvons que la m6thode pr6voit des textures qui, lorsque le maclage pr6domine, sont consid6rablement diff6rentes et en meiUeur accord avec rexp6rience que les sch6mas traditionnels qui r6orientent un grain entier lorsque qu'un certain crit~re est satisfait. On 6tudie syst6matiguement les diverses combinaisons de glissement et de maclage ainsi que les diverses combinaisons des contraintes critiques associ6es dans le cas du laminage, de la traction et de la compression des alliages de Zr. Une comparaison des diverses textures pr6vues et exp~rimentales conduit ~ la conclusion que la maclage dolt, en v6rit6, contrgler le d6veloppement de la texture.Zmmnmeafasaang--ln vielen Polykristallen von Materialien mit weniger als kubischer Symmetrie ist die plastische Verformung gepr~gt yon ZwiUingsbildung. Insbesondere behandeln wir hier den Fall des Zirkons und seiner Legierungen ausffihrlich. Wit schlagen eine neue Methode zur modeUhaften Beschreibung der Kornumorientierung durch Zwillingsbildung vor; die Methode beruht auf dem Verfahren der 'Obertragung des Volumanteils', mit dem auch die Gleitmoden beschrieben werden k6nnen. Diese Methode sagt Texturen voraus, die fiir den Fall, dal3 Zwillingsbildung vorherrscht, besser mit dem Experiment fibereinstimmen und die sich betr~chtlich yon denen unterscheiden, die mit herkgmmlichen Veffahren ermittelt werden, also bei denen ein ganzes Korn umorientiert wird, wenn ein bestimmtes Kriterium erf'ullt ist. Ffir die Fille des Walzens, der Zug-und der Druckverformung yon Zirkonlegierungen werden verschiedene Kombinationen von Gleit-und Zwillingsmoden und die zugeh6rigen kritischen Spannungen s...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.