Neutron Diffraction

Holden, T. M.

doi:10.1002/9781118402832.ch8

Cited by 19 publications

(22 citation statements)

References 31 publications

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“…At each measurement location, the number of neutrons measured across a small range of scattering angles by the detector is fitted to a Gaussian distribution and each location is sampled until a sufficient number of neutrons are detected to determine . The sampling time is dependent on the grain size of the material, the neutron flux of the incident beam, the gauge volume size and the path length of the beam inside the specimen (Holden, 2013). The uncertainty in fitting the Gaussian profile is used to determine the error in residual strain and stress measurements.…”

Section: Neutron Diffractionmentioning

confidence: 99%

Quantification of residual stresses in electron beam welded fracture mechanics specimens

Kapadia

Davies

Pirling

et al. 2017

International Journal of Solids and Structures

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Residual stress measurements have been made in a range of electron beam welded samples to study how the weld induced residual stresses redistributed during fabrication of compact tension, C(T), specimens. The samples were manufactured from Type 316H stainless steel in the ex-service material condition and in material which had been preconditioned by inducing 8% plastic strain. Measurements made using neutron diffraction, slitting and the contour method were generally in good agreement and showed residual stress components of up to three times the base material's yield strength existed in the samples. When sectioning a sample to perform the contour method, large elastic deformations occurred at the cut tip due to the large residual stresses present. A correction was applied to the measured surface displacements to account for this deformation. Neutron diffraction measurements were made at various stages of the fabrication process, which showed significant stress redistribution occurred as the welded samples were machined into C(T) specimens.However the tensile stresses near the crack tip of the C(T) specimens remained large and could significantly influence subsequent crack growth tests. Highlights Electron beam welding is shown to produce repeatable residual stress fields in thick samples

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Section: Neutron Diffractionmentioning

confidence: 99%

Quantification of residual stresses in electron beam welded fracture mechanics specimens

Kapadia

Davies

Pirling

et al. 2017

International Journal of Solids and Structures

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“…where σ agg is the macroscopic applied stress in the axial direction, ε ax, hk.l and ε rad, hk.l are the elastic strains of the grains contributing to the hk.l peak in the axial diffraction pattern as measured in the axial and radial directions respectively, and E hk.l and ν hk.l are hk.l-specific diffraction elastic constants (e.g. Hutchings et al, 2005, p.206-207;Holden, 2013). By definition the diffraction elastic constants relate the hk.l elastic strains to the macroscopic applied stress.…”

Section: Discussionmentioning

confidence: 99%

“…The practicalities of collecting neutron diffraction data from engineering materials during the type of deformation tests used in this study are described elsewhere (e.g. Daymond, 2006;Holden, 2013).…”

Section: Experimental Methodsmentioning

confidence: 99%

Using neutron diffraction to examine the onset of mechanical twinning in calcite rocks

Covey-Crump

Schofield

Oliver

2017

Journal of Structural Geology

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Experimental calibration of the calcite twin piezometer is complicated by the difficulty of establishing the stresses at which the twins observed in the final deformation microstructures actually formed. In principle, this difficulty may be circumvented if the deformation experiments are performed in a polychromatic neutron beam-line because this allows the elastic strain (and hence stress) in differently oriented grains to be simultaneously monitored from diffraction patterns collected as the experiment is proceeding. To test this idea small strain (<0.3%), uniaxial compression experiments have been performed on Carrara marble (grain size 150 µm) and Solnhofen limestone (5 µm) at temperatures of 20°-600°C using the ENGIN-X instrument at the ISIS neutron facility, UK. At the lowest temperatures (25°C Carrara; 200°C Solnhofen) the deformation response was purely elastic up to the greatest stresses applied (60 MPa Carrara; 175 MPa Solnhofen). The sign of the calcite elastic stiffness component c 14 is confirmed to be positive when the obverse setting of the calcite rhombohedral lattice in hexagonal axes is used. In the Carrara marble samples deformed at higher temperatures, elastic twinning was initiated at small stresses (<15 MPa) in grains oriented such that the Schmid factor for *Manuscript Click here to view linked References 2 twinning was positive on more than one e-twin system. At greater stresses (65 MPa at 200°C decreasing to 41 MPa at 500°C) there was an abrupt onset of permanent twinning in grains with large Schmid factors for twinning on any one e-twin system. No twinning was observed in the Solnhofen limestone samples deformed at 200° or 400°C at applied stresses of < 180 MPa. These results highlight the potential of this approach for detecting the onset of twinning and provide, through experiments on samples with different microstructures, a strategy for systematically investigating the effects of microstructural variables on crystallographically-controlled inelastic processes.

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“…A very surprising factor of two anisotropy was revealed by the first measurements on the disk, which used neutron diffraction and standard procedures (Holden, 2013;Santisteban et al, 2001;Zhang et al, 2003) at the SMARTS instrument at Los Alamos National Laboratory (Bourke et al, 2002). These measurements were performed using time-of-flight diffraction and then a Rietveld refinement (Von Dreele et al, 1982) to determine the lattice constant from multiple peaks.…”

Section: Residual Stress and Strain Measurementsmentioning

confidence: 99%

Amplified effect of mild plastic anisotropy on residual stress and strain anisotropy

Prime

2017

International Journal of Solids and Structures

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Highlights Axisymmetric indentation produced residual stresses in a disk of 2024 Aluminum  Mild plastic anisotropy caused severe anisotropy in residual stress and strain  Modeling showed that constraint effects caused the amplified stress anisotropy  Hookean elasticity explained the even more amplified residual strain anisotropy AbstractAxisymmetric indentation of a geometrically axisymmetric disk produced residual stresses by non-uniform plastic deformation. The 2024 aluminum plate used to make the disk exhibited mild plastic anisotropy with about 10% lower strength in the transverse direction compared to the rolling and through-thickness directions. Residual stresses and strains in the disk were measured with neutron diffraction, slitting, the contour method, xray diffraction and hole drilling. Surprisingly, the residual-stress anisotropy measured in the disk was about 40%, the residual-strain anisotropy was an impressive 100%, and the residual stresses were higher in the weaker direction. The high residual stress anisotropy relative to the mild plastic anisotropy and the direction of the highest stress is explained by considering the mechanics of indentation: constraint on deformation provided by the material surrounding the indentation and preferential deformation in the most compliant direction for incremental deformation. By contrast, the much larger anisotropy in residual strain compared to that in residual stress is independent of the fabrication process and is instead explained by considering Hookean elasticity. For Poisson's ratio of 1/3, the relationship simplifies to the residual strain anisotropy equaling the square of the residual stress anisotropy, which matches the observed results (2 ≈ 1.4^2). A lesson from this study is that to accurately predict residual stresses and strains, one must be wary of seemingly reasonable simplifying assumptions such as neglecting mild plastic anisotropy.

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Neutron Diffraction

Cited by 19 publications

References 31 publications

Quantification of residual stresses in electron beam welded fracture mechanics specimens

Quantification of residual stresses in electron beam welded fracture mechanics specimens

Using neutron diffraction to examine the onset of mechanical twinning in calcite rocks

Amplified effect of mild plastic anisotropy on residual stress and strain anisotropy

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