摘要:

A comparative study has been made of the mechanical behaviour of as-cleaved, chemically polished and coated lithium fluoride crystals. Surface coatings were produced by Vacuum deposition and by chemical reaction. Thin (≯ 10 μ) reacted-coatings increased the yield stress some 50% and were responsible for catastrophic stress drops observed at the critical resolved shear stress. Coatings also decreased the initial rate of work-hardening and the stress and strain to fracture. Failure occurred by the formation of Strch-type cracks.

ISSN:0031-8086    

DOI:10.1080/14786436008235877

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

Observations have been made by electron transmission microscopy of thin flakes of deformed magnesium oxide. The ease of cross slip of screw dislocations in this material has been directly verified. Cross slip leads to the formations of many markedly elongated prismatic loops of dislocation. These are observed Profusely within slip bands, produced at room temperature. They are unstable at higher temperatures and break up into numbers of smaller prismatic loops. From these observations a mechanism for the widening of slip bands, observed under the optical microscope, is proposed. Certain dislocation interactions have been observed and analysed and preliminary observations made of slip band intersections.

ISSN:0031-8086    

DOI:10.1080/14786436008235878

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

Cyclotron resonance effects of the Azbel'-Kaner type have;been observed in lead specimens at 9 kMc/sec and 1.2°k, and effective mass values of the charge carriers have been deduced from the magnetic field dependence of the surface resistance of the specimens. The anisotropy of the surface conductivity of the single crystal specimens in the low field limit was found to be consistent with the existing model of the Fermi surface in load, and from the value of the surface conductivity of a polycrystalline specimen, a value of the total Fermi surface area was found which supports the view that the fourth Brillouin zone in lead is empty.

ISSN:0031-8086    

DOI:10.1080/14786436008235879

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

Measurements have been made of the anisotropy of the optical absorption induced by neutron and electron irradiation. Some of the measurements were made with a six-plate fluorite polarizer, whose efficiency was found to be 65% at 2500 å, and which could be used at shorter wavelengths than a Clan-Thomson prism.

ISSN:0031-8086    

DOI:10.1080/14786436008235880

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

An attempt has been made to establish a mechanism for stress corrosion by direct observation on the propagation of cracks in α-brass tested under ammonia. The observations indicate that failure might be described by a two-stage process, of local embrittlement, followed by a cleavage-like fracture. Such a model demands that the embrittled zone should have its mechanical properties modified in such a way as to allow a crack to form and reach some critical velocity, whilst the normal unattacked metal should be able to support this free-running crack for extensive failure to occur. These requirements are examined in the light of current ideas on the metal physics of fracture.

ISSN:0031-8086    

DOI:10.1080/14786436008235881

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

ISSN:0031-8086    

DOI:10.1080/14786436008235882

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

Samples of pure artificial graphite have been irradiated with electrons at 79°k, and a study made of the annealing characteristics of the changes in electrical conductivity, Hall effect and magneto-resistance. All three quantities show an anomalous annealing range below 120°k, and a simplified band theory calculation indicates that the concentration of both electrons and positive holes increase during irradiation and also in the anomalous annealing range.

ISSN:0031-8086    

DOI:10.1080/14786436008235883

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

摘要:

The theory of phonon drag in the thermoelectric power is developed from an equation derived in a previous paper. It is shown that important in the understanding of the phenomena are the relative probabilities 'α (jq;q+K)that a phonon of wave vectorqand polarizationjwill interact with electrons via a process of umklapp typoK, whereKis a reciprocal lattice vector or zero. α(jq, q+K) is the probability relative to all the processes into which thejqphonons can enter, including phonon-phonon collisions and phonon-impurity interactions. It is shown by means of a 'baby spectrum' that the use of α results in the domination of the phonon drag effect by the transverse-like phonon modes, and in the watering down of any ‘bulge’ effect of the Fermi surface. Rough calculations are made that show that one can get qualitative agreement with experiment over at least part of the temperature range from 2 to 20°k. It is shown that with neglect of phonon-phonon and phonon-impurity interactions the phonon drag partSgof the thermoelectric power is the sum of two terms. a normal (negative) termSg-, which is exactly what would be calculated if all processes mere non-umklapp processes. plus a term Sg+ which is anomalous (positive) in sign and is the effect on the electrons of the Bragg reflections abstracted from the umklapp processes. A simple derivation of the basic equation is given.

ISSN:0031-8086    

DOI:10.1080/14786436008235884

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor

ISSN:0031-8086    

DOI:10.1080/14786436008235885

出版商:Taylor & Francis Group    

年代:1960

数据来源: Taylor