To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure firstname.lastname@example.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Depth profiles of intrinsic in-plane, biaxial stresses were obtained as a function of τ, the 1/e penetration depth, in a 1.0 um thick planar d. c. magentron sputter deposited molybdenum film using asymmetric grazing incidence x-ray diffraction (GIXD). τ was varied between 20 and 276 Å. The stresses σ11 and σ22 were characterized in the directions parallel and perpendicular to the long axis of the cathode respectively using a cos2φ method. The results show that starting from τ=17Å, σ11 and σ22 are compressive and become rapidly more compressive with a minimum at τ ∼ 20 - 40 Å thereafter increasing gradually toward tensile values. The reasons for the shape of the stress gradient are not well understood but may be related to the relaxation of the stresses at the tops of the columnar Zone T-type microstructure and to the oxygen gradient in the film.
This paper reports and discusses the results of a computer modeling study on powder diffraction profile analysis for crystallite size and strain of polycrystalline materials. The results of this computer modeling show that if the spans of diffraction profiles in reciprocal space (1/d) are not carefully chosen, an overestimation on size and an underestimation on strain may result in analysis by both the Warren-Averbach and the Hall-Williamson methods. A general way to eliminate such errors based on profile fitting and regeneration is presented and discussed in this paper.
Neutron powder diffraction techniques have been used to characterize the pseudo-macro (PM) residual stresses in ZrO2(CeO2)/Al2O3 ceramic composites as a function of ZrO2(CeO2) volume fraction and fabrication procedures. The diffraction data were analyzed using the Rietveld structure refinement technique. From the refinement, we found that the CeO2 stabilized tetragonal ZrO2 particles were in tension and the Al2O3 matrix was in compression. Different sintering time had little impact on the PM stresses. On the other hand, the magnitude of the PM stresses in both ZrO2 and Al2O3 decreased linearly with the increase of their volume fractions.
Hematite (α-Fe2O3) powder compacts have been subjected to controlled, quantitative high pressure shock loading at peak pressures from 8-27 GPa and preserved for post shook analysis. The broadened x-ray diffraction peak profiles have been analyzed to determine the residual lattice strain and the coherent crystallite sizes. Maximum modification effects are observed near 17 GPa with strain values near 3 x 10-3 and size values near 200 Å suggesting annealing at higher shock pressure, resulting from the higher shock temperature.
The morphology of englacial drainage networks and their temporal evolution are poorly characterised, particularly within cold ice masses. At present, direct observations of englacial channels are restricted in both spatial and temporal resolution. Through novel use of a terrestrial laser scanning (TLS) system, the interior geometry of an englacial channel in Austre Brøggerbreen, Svalbard, was reconstructed and mapped. Twenty-eight laser scan surveys were conducted in March 2016, capturing the glacier surface around a moulin entrance and the uppermost 122 m reach of the adjoining conduit. The resulting point clouds provide detailed 3-D visualisation of the channel with point accuracy of 6.54 mm, despite low (<60%) overall laser returns as a result of the physical and optical properties of the clean ice, snow, hoar frost and sediment surfaces forming the conduit interior. These point clouds are used to map the conduit morphology, enabling extraction of millimetre-to-centimetre scale geometric measurements. The conduit meanders at a depth of 48 m, with a sinuosity of 2.7, exhibiting teardrop shaped cross-section morphology. This improvement upon traditional surveying techniques demonstrates the potential of TLS as an investigative tool to elucidate the nature of glacier hydrological networks, through reconstruction of channel geometry and wall composition.
Glen’s flow law is a well-established general law for steady-state glacier ice deformation, and many laboratory tests and field measurements have been undertaken which have shown the generality of the law to be correct. In Nature, ice deformation is the response of the glacier/ice sheet to the applied self-weight stress of the ice mass (i.e. ice thickness, gravity and ice density) which produces a stress gradient within the ice column. Detailed experimental analyses of ice samples in the laboratory have until now only been undertaken using uniform stress fields in uniaxial or triaxial tests. Obviously the best method for investigating ice in the laboratory would be if stress gradients similar to those found in Nature could be replicated. In the following paper we describe the physical modelling of two (laboratory-prepared) isotropic, polycrystalline ice models (0.75 × 0.25 × 0.18 m) at enhanced gravity levels (80g) in a geotechnical beam centrifuge. Steel plate was placed on top of the ice model, replicating an overburden of approximately 36 m of ice (at 80g). Thus we were able to model the deformation of the lower 14 m of an ice mass approximately 50 m thick. Models are confined laterally by the Perspex strongbox walls, preventing lateral extension within the sample during testing. Models are unconfined on their downslope ends, rendering longitudinal stresses negligible. Deformation can therefore be treated as simple shear. Samples are instrumented with displacement markers and thermocouples. Values for A and n in the flow law derived from the experiments are reasonable and indicate the potential of this method for ice-deformation studies.
Simultaneous use of neutron diffraction and attenuation based transmission Bragg edge imaging for strain measurements is demonstrated in this paper using the pulse neutron source at Los Alamos National Laboratory. Cylindrical samples made from ferritic steel have been subjected to in-situ elastic loading in tension and torsion. Lattice strains were investigated for both deformation modes by time-of-flight (TOF) neutron diffraction using two detector banks at 2θ of ±90°. At the same time, the transmitted portion of the neutron beam was recorded with the goal to analyze the position and shape of the Bragg edges, using a novel time/energy resolved Microchannel Plate (MCP) detector with pixel size of 55 µm and a 28x28 mm2 field of view. Lattice strains obtained using neutron diffraction indicate that the deformation path (tension versus torsion) has important effect on their evolution and related results are summarized.
The emphasis of this paper is to explain the aspects of the experimental setup and data interpretation associated with neutron Bragg edge transmission technique for obtaining through-thickness averaged strain measurements. Implications of using transmission imaging based strain mapping for samples subjected to deformation under tensile loading (where stress at a given cross-section is constant) versus torsional loading (where stress varies linearly from center to outer radius) are discussed. In the case of samples subjected to tensile loading, analysis of the Bragg edge shifts provides the strain value in the direction of the transmitted beam. Thus, three strain components are measured simultaneously when performing Bragg edge imaging in addition to diffraction using two detector banks. For specimens subjected to pure shear by torsion, the Bragg edge transmission technique cannot readily provide quantitative strain information as the mid-point of the Bragg edge does not shift uniformly due to external loading, but results in a broadening of the Bragg edge. Such information can be used to describe the variation of strain distribution along the transmitted beam direction. Spatially resolved Bragg edge maps will be very helpful to detect d-spacing inhomogeneities within the illuminated volume, which may remain undetected when using diffraction only measurements.
Target modification by excimer laser exposure has been investigated. Under conditions typical in the fabrication of superconducting thin films, deposition rate decreases with exposure and significant physical and chemical modifications occur on the target surface. These modifications do not inhibit congruent evaporation.