Harper-Dorn creep

Kassner ME, Kumar P, Blum W (2007)

Publication Language: English

Publication Type: Journal article

Publication year: 2007

Journal

International Journal of Plasticity Elsevier

Book Volume: 23

Pages Range: 980-1000

Journal Issue: 6

DOI: 10.1016/j.ijplas.2006.10.006

Abstract

The fundamental mechanism of time-dependent plasticity, or creep, of crystalline materials at very low stress is, at present, particularly controversial. At "moderate" stresses above about 0.6 Tm, over a wide range of stresses, five-power-law creep is observed that is widely believed to be dislocation climb-controlled, with the activation energy for creep to be close to that of vacancy diffusion. Steady-state creep (Stage II or secondary creep) is usually described by the steady-state stress exponent, n, which is typically 4-7. At lower stresses, Harper-Dorn has usually been the mechanism suggested to occur. The relation between the applied stress and the steady-state creep-rate for Harper-Dorn creep is phenomenologically described byover(ε, ̇)ss = AHD fenced(frac(Dsd Gb, kT)) fenced(frac(σ, G))1where AHD is a constant. Since these early observations, Harper-Dorn creep has been reported to occur in many materials. Recent observations have suggested that in Al (the most extensively studied system) and all other systems, Harper-Dorn may be artificial in that the high creep rates may be a consequence of additional or unusual restoration mechanisms that do not normally occur in five-power-law creep or tensile fracture. These restoration mechanisms include dynamic recrystallization and/or grain growth. Others have suggested that Harper-Dorn is also artificial but because the strain-rates reported were not genuinely steady-state and, consequently, as much as an order of magnitude higher than genuine steady-state behavior. Others also found that they could not reproduce the original Al data of Harper and Dorn, for unknown reasons. The analysis of other materials in which Harper-Dorn has been proposed to occur has been placed in question. © 2006 Elsevier Ltd. All rights reserved.

Authors with CRIS profile

Wolfgang Blum Technische Fakultät

Additional Organisation(s)

Lehrstuhl für Werkstoffwissenschaften (Allgemeine Werkstoffeigenschaften)

Involved external institutions

University of Southern California (USC) US United States (USA) (US)

How to cite

APA:

Kassner, M.E., Kumar, P., & Blum, W. (2007). Harper-Dorn creep. International Journal of Plasticity, 23(6), 980-1000. https://doi.org/10.1016/j.ijplas.2006.10.006

MLA:

Kassner, Michael E., Praveen Kumar, and Wolfgang Blum. "Harper-Dorn creep." International Journal of Plasticity 23.6 (2007): 980-1000.

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