Strain rate sensitivity: The role of dislocation loop and point defect recovery

Saimoto, S.; Duesbery, M. S.

doi:10.1016/0001-6160(84)90212-8

Cited by 28 publications

(5 citation statements)

References 22 publications

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“…2) and indicate that elimination of the fraction of obstacles that are transparent to dislocations, and do not contribute to the flow stress at lower strain rates, results in an increase in the strain-rate sensitivity of the material. The data are in agreement with studies of plastically deformed Al by Saimoto and Duesbery [30], who observed increased strain-rate sensitivity after annealing samples above 300 K, which was attributed by the authors to the recovery of point defect clusters and submicroscopic dislocation loops.…”

Section: Thermally Activated Plastic Flowsupporting

confidence: 92%

Thermally activated flow of dislocations in Al–Mg binary alloys

2015

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Section: Thermally Activated Plastic Flowsupporting

confidence: 92%

Thermally activated flow of dislocations in Al–Mg binary alloys

2015

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“…Nevertheless despite this complexity, overall the results suggest that the computer models of dislocation flow through dispersed obstacles is reaffirmed. Some of the ambiguity of debris identification is reduced if dynamic recovery at 298 K [22] is avoided. By testing at 78 K at which recovery does not occur, an estimate of the strength of debris α deb can be made as follows.…”

Section: Resultsmentioning

confidence: 99%

Forensic Analyses of Stress-Strain Diagrams to Evaluate Contributions from Microstructure

Saimoto

Langille

Niewczas

2018

MSF

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The conventional characterization of work-hardening is to approximate the stress-strain diagram using the empirical curve-fitting of Hollomon or Voce. The new method uses the Taylor slip analyses to derive a functional form which is optimally fitted to the data. This constitutive relations analysis (CRA) duplicates the data using at least two fit loci. The fit parameters relate to the slip motion within the microstructure and hence its interpretation reveals the possible dynamic shape-change reactions. The fit-process defines a new yield stress which separates the yielding from the deformation mechanisms at large strains that breaks up into two regions separated by intersection parameters. The applications of CRA to nanovoid formation and growth leading to ductile failure, plane stress yield locus prediction using tensile tests and decoding the stress-strain diagram for age-hardened aluminum alloys have been successful. Using super-pure aluminum, this study confirms that CRA is based on crystal plasticity principles and that CRA can predict the correlation of the obstacle strength factor, α, with work-hardening, hence permitting conversion of flow stress at given strains to obstacle density. The derived results show that the inherent annihilation process and the changing strength factor are coordinated to result in a self-consistent constitutive relation.

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“…One explanation for this bifurcation could be dissolution of the solute clusters into smaller more complex objects, as described by Chen et al [50] for Al-Cu, which ultimately decreases the apparent activation volume via a decrease in both the activation distance, d, and spacing of the obstacles, l, such that V' = bdl decreases. An alternative mechanism for the decrease could be dislocation interactions in the solute cluster field during straining generating dislocation debris (small loops), which are weak obstacles that recover rapidly during the downchanges, though this effect is unexpected at such low strains [51], [52] Based on the calculated S values shown for the three alloys in Figure 7, it is possible to estimate the activation distance, representative of the size of the rate-controlling obstacles, based on the relationship:…”

Section: Discussionmentioning

confidence: 99%

“…The likely cause of this is the ability for dislocation-dislocation and dislocationsolute/cluster interaction products to be recovered during the down-change strain rate change [53] whereby there is an effect on the spacing l, rather than d. Niewczas and Park [53] showed that in pure Al, dislocation-dislocation interaction products do not anneal out at temperatures below 100K; in contrast, such recoverable components must be considered here. Saimoto [29] and Saimoto and Duesbery [51] have argued that the presence of these dislocation interaction products contribute to the SRS in the down-change at ambient temperatures due to their likelihood to anneal out during the rate-change; in the strain rate change test, this effect would appear as an added relaxation during a perfectly compensated strain rate change. This would be coupled with the extensive work performed by Niewczas [52], [53] for observing the dislocation interaction products at low temperatures and the corresponding annealing temperatures, and how they influence the flow stress.…”

Section: Discussionmentioning

confidence: 99%

Asymmetry of strain rate sensitivity between up- and down-changes in 6000 series aluminium alloys of varying Si content

Langille

Diak

Geuser

et al. 2020

Materials Science and Engineering: A

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Increasing demand for a reduction in fuel emissions in passenger vehicles has generated the need for lighter weight materials to be used in automobile manufacture for body-in-white applications. Aluminium alloys in the 6000-series, containing Mg and Si are ideal candidates for these applications but lack the formability found in commonly used steels, providing a need to more fully understand the factors influencing the formability of these alloys at high strains. Conventionally, a high strain rate sensitivity (SRS) is tied to increased formability because it retards the increase in the local strain rate found in the diffuse neck interior. However, most experimental work neglects that the regions exterior to the neck will undergo a local decrease in the strain rate which causes a corresponding material softening. Observations of an asymmetry between up-change and down-change SRS of these alloys in the natural aged condition show that different mechanisms are controlling the SRS depending on the direction of rate change. Following a characterization of the state of clustering by differential scanning calorimetry, continuous tensile and precision strain rate sensitivity testing results are presented, elucidating the differences between the up-change and down-change SRS tests. It is shown that these differences are due to the activation of different thermal obstacles during the two directions of rate changes. The role of a change in Si content on the mechanical properties is explored and its suspected role on the asymmetric SRS is discussed.

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Strain rate sensitivity: The role of dislocation loop and point defect recovery

Cited by 28 publications

References 22 publications

Thermally activated flow of dislocations in Al–Mg binary alloys

Thermally activated flow of dislocations in Al–Mg binary alloys

Forensic Analyses of Stress-Strain Diagrams to Evaluate Contributions from Microstructure

Asymmetry of strain rate sensitivity between up- and down-changes in 6000 series aluminium alloys of varying Si content

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