Neutron scattering residual stress measurements on gray cast iron brake discs Page: 3 of 5
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OUTBOARD
INBOARDFig. 2 - Schematic view of
diameter of the brake disc.the cross section through the
Fig. 1 - Photograph of brake disc with outboard side to the
front left and inboard side to back right.
The material is a gray cast iron with a graphite flake
microstructure where the spatial scale of the microstructure
varies through the thickness of the material and presumably
depends on the cooling conditions of these cast materials.
The residual stress state under consideration arises during
rapid non-uniform cooling of the cast metal and the
associated differentials in thermal contraction.
Crystallographic texture in the samples dictated the
choice of the particular Bragg diffraction planes used in the
neutron scattering strain measurement experiments. The
number of grains contributing to the diffraction peak was
increased by oscillating the sample a few degrees about the
diffractometer axis during data collection when the scattering
geometry permitted.
Neutron scattering experiments were carried out on the
HB-2 spectrometer at the High Flux Isotope Reactor (HFIR)
of the Oak Ridge National Laboratory. The incident
neutron beam was made monochromatic by diffraction from
the (11.0) planes of a beryllium single crystal. Details of
the method have been reported elsewhere (4). The scattering
volume was defined by scattered beam apertures of 2mm
width and either 2mm or 10mm height placed close to the
diffractometer axis. Calibration of the diffractometer and the
position-sensitive detector was determined using a nickel
powder standard.The axial and radial components of residual strain were
measured with a gauge volume having a 2mm by 2mm base
and 10mm height. In the measurement of hoop
components the gauge volume was a cube with 2mm sides.
The sample was mounted on an automated X-Y-Z
translation table and the coordinates of the sampling
positions were referenced with respect to the surfaces of the
disc. The locations of the external surfaces of the disc were
verified by making fitting an intensity-position scan using a
non-linear fit to the intensity (5).
Macroresidual strain is determined from the shift in
lattice d-spacing of diffracting grains relative the d-spacing
of a strain-free reference material. The strain is an average
of the strains in the large number of diffracting grains
within the sampling volume. Bragg's law relates the
angular location of the diffraction peak determined in the
scattering measurement to the lattice d-spacing by:da =
2sine,Eq. 1
where X is the wavelength of the neutrons and Ohi is one-
half the scattering angle for a diffraction peak corresponding
to the crystallographic Miller indices h,k,l. The residual
strain component is related to the shift in d-spacing by:=d - dW
dL,Eq. 2
where dj is the d-spacing of the stress-free reference.
The direction of the measured strain bisects the incident and
scattered beams. Substitution of Bragg's law into this
strain equation gives, equivalently:sin0 -1
sin 9hEq. 3
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Spooner, S.; Payzant, E. A. & Hubbard, C. R. Neutron scattering residual stress measurements on gray cast iron brake discs, article, November 1, 1996; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc679947/m1/3/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.