摘要:

Cracked Cu specimens, made by diffusion bonding two halves of a single crystal, were 3-point bend tested, and the surfaces near the crack tips were examined by an optical microscope and a stylus profilometer. The plastic zone developed as assembled fan-shaped sectors, the details of which depended on the crystal orientation. A sector was often characterized by a family of dominant slip lines, and operations of slips on coplanar slip planes (CSP) were mutually exclusive. The through-thickness displacement changed gradually across sector boundaries but its gradient did not, suggesting a constant plastic strain within a sector but strain discontinuites at sector boundaries. The degree of necking depended mostly on the operation of slips on non-CSP, but operation of CSP caused either local necking or protrusion depending on the crystal orientation.

ISSN:0950-0839    

DOI:10.1080/09500839108214540

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Transmission-electron-microscopic evidence reveals the existence ofbothrhombohedra1 model structures, RS1 and RS2, which have previously been proposed to explain the ordering phenomena observed in Si1−xGex. alloy layers and in the boundary regions of Si-Ge strained-layer superlattices. Composition, annealing time and residual strain in the material are parameters determining the formation of either one of the two or of both structures. Only one of the two phases, RS1, is found to be reversible.

ISSN:0950-0839    

DOI:10.1080/09500839108214541

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Ceramics are notorious for their ‘brittleness’, i.e. the sensitivity of mechanical strength to flaws on the microstructural scale. The associated notion of the ‘critical flaw’ has dominated design considerations concerning structural reliability and materials processing of ceramic components. This accounts for the trend over the last decadetowards a processing strategy of elimination strength-degrading flaws at source. Here we propose a fundamentally different approach, that of processing ceramics with crack-impeding elements integrated into the indigenous microstructures, such that any pre-existing or service-induced flaws are effectively stabilized. Strength data on a tailored alumina/aluminium-titanate material demonstrate the capacity of our approach to produce simple ceramics with unique flaw insensitivity.

ISSN:0950-0839    

DOI:10.1080/09500839108214542

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Neutron diffraction data were obtained from quasicrystals of the AlPdMn system and the isomorphic modifications AlPd(FeCr). From contrast variation effects, partial structure factors were determined. In the high-dimensional periodic description, the structure can be viewed as a six-dimensional cubic lattice belonging to the Pmspace group, with a superstructure due to a chemical order which somewhat induces an F-type lattice.

ISSN:0950-0839    

DOI:10.1080/09500839108214543

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The concept of a disclination is modified to apply it to composite bodies with wedge-like inhomogeneities. It is found that the problem of a wedge disclination lying along the vertex of the inhomogeneity is not a well-posed elasticity problem and the stresses exhibit various anomalies.

ISSN:0950-0839    

DOI:10.1080/09500839108214544

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Some consequences of the spin-bipolaron theory of high-Tc, superconductivity are discussed in the light of recent experimental results. These include speculations on the nature of the bosons, their presence above Tc, the linearρ-Tcurve for the resistivity and exceptions to it, recent results on the thermopower, the isotope effect, infrared absorption, and the Hall effect.

ISSN:0950-0839    

DOI:10.1080/09500839108214545

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We report the effect of hydrostatic pressure on the resistivity anomaly in KMo6O17resulting from charge-density-wave (CDW) formation. The rate ofdecay of the Peierls temperature with pressure is δTp/δp= −2Kkbar−1for p>6kbar and δTp/δp= +l0K kbar−1for p>6kbar. The observed behaviour is ascribed to two competing mechanisms. At low pressures, interlayer couplings and a stiffening of the lattice are involved. At higher pressures, intralayer couplings and a strong enhancement of the density of states at the Fermi level are responsible for the large increase ofTpobserved.

ISSN:0950-0839    

DOI:10.1080/09500839108214546

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The recombination mechanism in a-Si: H is examined by studying the lifetime distribution P(τ) of the photoluminescence using frequency-resolved spectroscopy (FRS) and by light-induced electron spin resonance (LESR). The experiments are performed in a wide range of excitation densities (1016cm−3s−1<G < 1022cm−3s−1). Two ranges of distinctively different behaviour are observed: (1)AtG > 5 × 1019cm−3s−1,P(τ) shifts with G to shorter times, as one expects in a case of non-geminate recombination between nearest available neighbours. (2) At G < 5 × 1018cm−3s−1, P(τ) is independent ofG. The transient behaviour of the photoluminescence intensity and of the LESR spin density shows convincingly that in this range geminate recombination prevails.

ISSN:0950-0839    

DOI:10.1080/09500839108214547

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The non-radiative efficiencyηnrhas been directly measured in hydrogenated amorphous silicon using photo-pyroelectric spectroscopy, for photon energies ranging from 1·5 to 2·2 eV at room temperature. The non-radiative efficiency is fairly constant for above-bandgap illumination, but displays a sharp minimum for photon energies near the bandgap energy.ηnrincreases with sub-bandgap illumination, saturating at a value roughly one half as large as its high-energy value.

ISSN:0950-0839    

DOI:10.1080/09500839108214548

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor