Harper-Dorn Creep — a Myth?

Harper-Dorn Creep - A Legend Attenuated?

“…The observations of Blum and Maier [1] on aluminium of 99.99% purity agree with the earlier observations. The lowest stress they applied was 0.093 MPa, at or just above the stress at which power-law creep begins to predominate.…”

“…Recently, Blum and Maier [1] published a paper entitled "Harper-Dorn Creep -a Myth?". They report experiments on 99.99% pure aluminium creeping at low strain rates in which the stress exponent is always much larger than unity, and conclude that "this indicates that Harper-Dorn creep as a unique dislocation mechanism with Newtonian viscosity may not exist".…”

Fifty years of Harper–Dorn creep: a viable creep mechanism or a Californian artifact?

“…However, the evidence for a purity effect tends to be negated by the subsequent work of Lee and Ardell [33], conducted at the University of California, Los Angeles, where excellent agreement was obtained with the behavior anticipated for Harper-Dorn creep in experiments conducted on single crystals of Al of 99.99% purity with the crystals tested in compression using parallelepiped samples with an acceptable aspect ratio of 2. As already noted, the later work of Blum and Maier [19] in Germany, where Harper-Dorn creep was not observed in 99.99% purity Al single crystals, is inconclusive because the tests were conducted on compression samples using an unacceptably low aspect ratio of~1 where it is reasonable to anticipate, as indeed reported, that the measured strain rates will be exceptionally low by comparison with the rates anticipated for the Harper-Dorn process.…”

“…Subsequently, Blum and Maier [19] published a paper titled ''Harper-Dorn Creep-a Myth?'' in which, based on their own experimental observations on pure polycrystalline aluminum tested in compression at 923 K, they argued against the concept of Harper-Dorn creep because they failed to find a transition to a region of n % 1 at their lowest stresses.…”

“…Furthermore, the arguments in favor of Harper-Dorn creep were later put forward in a spirited defense by Nabarro [21] entitled ''HarperDorn Creep-A Legend Attenuated?'' where it was noted that the determinations of the stress exponent by stress change testing in the experiments of Blum and Maier [19] ''were made at stresses above those at which Harper-Dorn creep is known to give way to power-law creep.'' By contrast to the debate on the relative merits of Harper-Dorn creep, Ruano et al [22] developed an alternative approach in a paper titled ''Evidence for Nabarro-Herring Creep in Metals: Fiction or Reality?''…”