X-ray Elastic Constants for β-SiC and Residual Stress Anisotropy in a Hot-Pressed Al2O3/SiC(Whisker) Composite

1990 ◽  
Vol 34 ◽  
pp. 643-650
Author(s):  
Paul Predecki ◽  
Alias Abuhasan ◽  
Charles S. Barrett
Keyword(s):  
Residual Stress ◽  
Elastic Constants ◽  
Crystal Data ◽  
X Ray ◽  
Residual Macrostresses ◽  
The Matrix ◽  
Average Residual ◽  
Residual Strains ◽  
Residual Microstresses ◽  
Ray Methods

AbstractX-ray elastic constants for the 511+333 and the 422 reflections of β-SiC were calculated from the single crystal data of Tolpygo using the Voigt-Reuss, Eshelby-Kroner and x-ray methods. Agreement was satisfactory for the 511+333, but less so for the 422. A hot-pressed α-Al2O3/ 29 vol % β-SiC (whisker) composite was investigated on its 3 principal faces. The total residual strains were found to be consistently anisotropic on all 3 faces suggesting that texture was present in the whiskers as a result of hot-pressing. Assuming no texture in the matrix, it was found possible to determine the average residual microstresses in the whiskers using the theory of Noyan and Cohen, without needing to know the whisker elastic constants or texture. The average microstresses were determined in each phase as well as the average residual macrostresses on each face.

Residual Stress Measurements in Continuous Fiber Titanium Matrix Composites

1992 ◽  
Vol 36 ◽  
pp. 481-488 ◽  
Author(s):  
M. R. James ◽  
M. A. Bourke ◽  
J. A. Goldstone ◽  
A. C. Lawson
Keyword(s):  
Residual Stress ◽  
Neutron Diffraction ◽  
Thin Sheet ◽  
Matrix Composites ◽  
X Ray ◽  
Residual Stress State ◽  
Longitudinal Residual Stress ◽  
The Matrix ◽  
Reinforcement Fiber ◽  
Residual Strains

AbstractMetal matrix composites develop residual strains after consolidation due to the thermal expansion mismatch between the reinforcement fiber and the matrix. X-ray and neutron diffraction measured values for the longitudinal residual stress in the matrix of three titanium MMCs are reported. For thick composites (> 6 plies) the surface stress measured by x-ray diffraction matches that determined by neutron diffraction and therefore represents the stress in the bulk region consisting of the fibers and matrix. For thin sheet composites, the surface values are lower than in the interior and increase as the outer rows of fibers are approached. While a rationale for this behavior has yet to be developed, accounting for composite thickness is important when using x-ray measured values to validate analytic and finite element calculations of the residual stress state.

Direct X-Ray Measurement of Residual Strains in Textured Steel

1983 ◽  
Vol 27 ◽  
pp. 197-206
Author(s):  
C. P. Gazzara
Keyword(s):  
Residual Stress ◽  
Crystal Lattice ◽  
Elastic Constants ◽  
Random Distribution ◽  
Elastic Anisotropy ◽  
X Ray Diffraction ◽  
X Ray ◽  
Residual Strains ◽  
Residual Stress Analysis ◽  
Textured Materials

One of the most detrimental effects on the accuracy of an X-ray diffraction residual stress analysis, XRDRSA(l), is found in the examination of textured materials. The degree of elastic anisotropy and texture is in general agreement with the extent of the error in the residual stress. Several approaches have been made to correct for the effects of texture, particularly involving experimental techniques. Reviews of such efforts are given by H. D811e(2), v.M. Hauk﹛3) and G. Maeder, J.L. Lebrun and J.M. Sprauel (4), just to mention a few.A brief chronology of the texture corrections involved in XRDRSA follows. With isotropic materials the d spacing of a crystal lattice, d, is assumed to vary linearly with sin2ψ. With textured materials the d vs sin2ψ relationship is nonlinear. This is due to the anisotropy of the elastic constants and their departure from a random distribution, or taking on a preferred orientation.

Residual Stress Determination in Al2O3/SiC (Whisker) Composites By X-Ray Diffraction

1987 ◽  
Vol 31 ◽  
pp. 231-243 ◽  
Author(s):  
Paul Predecki ◽  
Alias Abuhasan ◽  
Charles S. Barrett
Keyword(s):  
Residual Stress ◽  
Profile Analysis ◽  
Peak Shift ◽  
Stress Determination ◽  
X Ray Diffraction ◽  
X Ray ◽  
The Matrix ◽  
Sic Whiskers ◽  
Residual Strains ◽  
Two Phases

Residual strains and stresses were determined in both phases of a hot pressed α-Al2O3 composite containing 25 wt % β (cubic) SiC whiskers using conventional x-ray diffraction and profile analysis. Both phases in this composite were randomly oriented as confirmed by back reflection pinhole photographs. The reflections found most useful with Cu Kα radiation were: 511 + 333 for β-SiC at -134° 2θ and 146 for α-Al2O3 at -136° 2θ. The peak shift and broadening observed in these reflections, relative to the starting powders, were largely due to the two phases mutually constraining each other elastically. This was confirmed by the reversal of the peak shift and most of the broadening in the SiC reflections when the Al2O3 matrix was etched away. Using the method of Cohen and Noyan, it was found possible to separate the macrostresses from the microstress components in each phase. The microstresses were largely hydrostatic; of the order of 895 MPa (130 ksi) compressive in the whiskers and 370 MPa (54 ksi) tensile in the matrix. The macrostresses were ~79 MPa (11.5 ksi) tensile.

Redetermination of Co4Nb2O9 by single-crystal X-ray methods

2006 ◽  
Vol 62 (5) ◽  
pp. i117-i119 ◽  
Author(s):  
María A. Castellanos R. ◽  
Sylvain Bernès ◽  
Marina Vega-González
Keyword(s):  
Single Crystal ◽  
High Precision ◽  
Cation Distribution ◽  
Crystal Data ◽  
Space Group ◽  
X Ray ◽  
Ray Methods

A high-precision structure of tetracobalt diniobium nonaoxide, Co4Nb2O9, is presented, based on X-ray single-crystal data. The space group and cation distribution previously obtained from powder data [Bertaut, Corliss, Forrat, Aleonard & Pauthenet (1961). J. Phys. Chem. Solids, 21, 234–251] are confirmed.

Residual stresses in a SiC whisker-reinforced alumina composite by high-temperature X-ray diffraction

1994 ◽  
Vol 9 (1) ◽  
pp. 50-53 ◽  
Author(s):  
Benjamin L. Ballard ◽  
Paul K. Predecki ◽  
Camden R. Hubbard
Keyword(s):  
Residual Stress ◽  
Single Crystal Silicon ◽  
Linear Extrapolation ◽  
X Ray Diffraction ◽  
Crystal Silicon ◽  
X Ray ◽  
Fine Grained ◽  
Silicon Carbide Whiskers ◽  
Alumina Composite ◽  
Residual Strains

Residual strains and microstresses are evaluated for both phase of a hot-pressed, fine-grained α-alumina reinforced with 25 wt% (29 vol%) single-crystal silicon carbide whiskers at temperatures from 25 to 1000 °C. The sample was maintained in a nonoxidizing environment while measurements of the interplaner spacing of alumina (146) and SiC (511 + 333) were made using X-ray diffraction methods. The residual strains were profiled at temperature increments of 250 °C from which the corresponding microstresses were calculated. Linear extrapolation of the SiC ε33 profile indicates that the strains are completely relaxed at a temperature of approximately 1470 °C. These residual stress relaxation results suggest that elevated temperature toughness and fracture strength of this composite may result from cooperative mechanisms.

The Meed for Experimentally Determined X-ray Elastic Constants

1976 ◽  
Vol 20 ◽  
pp. 355-367 ◽  
Author(s):  
R. H. Marion ◽  
J. B. Cohen
Keyword(s):  
Residual Stresses ◽  
Elastic Constants ◽  
X Ray Diffraction ◽  
X Ray ◽  
Residual Strains ◽  
Entire Specimen ◽  
Representative Material

In order to convert residual strains measured by x-ray diffraction techniques into residual stresses, appropriate x-ray elastic constants have to be measured. Since these x-ray elastic constants may depend on the metallurgical state, deformation, and entire specimen history, errors in stress values may result if the constants are not measured for representative material states. In the present work, it is shown that in same cases these errors may be large.

Detection Confirmation and Determination of Trace Amounts of Selenium by X-Ray Methods

1963 ◽  
Vol 7 ◽  
pp. 542-554
Author(s):  
Frank L. Chan
Keyword(s):  
Matrix Effects ◽  
Hexagonal Structure ◽  
Elemental Selenium ◽  
X Ray Diffraction ◽  
X Ray ◽  
Yellow Color ◽  
The Matrix ◽  
Ray Methods ◽  
Tetravalent State

AbstractRecently, interest in the determination of selenium in trace amounts has been greatly intensified because of the nutritional aspects of this element. It has been reported that selenium in the amount of 13 μg in the form of sodium selenite in 100 g of feed has an effect similar to that of vitamin E. In the field of semiconductors, the detection and determination of trace amounts of selenium in arsenic, antimony, and small single crystals of solid solution of cadmium selenide and sulfide are of considerable importance in semiconductor performance.In the Aerospace Research Laboratories, 4,5 diamino-6-tbiopyi-imidine has been successfully adopted as a reagent for the spectrophotometric determination of selenium. The reaction of 4,5 diamino-6-thiopyrimidine and tetxavalent selenium produces a yellow color with the formation of elemental selenium. It is possible to determine elemental selenium by collecting it in a thin layer. The selenium deposited in this layer may then be determined by an X-ray fluorescence method. A procedure of this nature has the advantage of eliminating the matrix effects commonly encountered in X-ray fluorescence. Furthermore, the slow generation of selenium affords a convenient means of detection and confirmation of this element by the use of X-ray diffraction procedures. By this technique selenium is first converted to its tetravalent state and is then reacted with 4,5 diamino-6-thiopyrimidine. On standing, the selenium is reduced to a red precipitate of elemental selenium which can be dissolved in carbon disulfide. Finally, the selenium can be converted into its hexagonal structure by annealing at 205-207°C.

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