FIFTH CANADIAN CONFERENCE ON NONDESTRUCTIVE ... - IAEA

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The commercial prototype is expected to be ready for testing in
December 1984. It consists of the head (Fig. 7), a stand, a 10 m umbilical
cord and a services package containing analysis electronics, computer,
X-ray power supply, closed circuit cooler, detector gas supply and
motor controllers. The head will weigh ~15 kg, the simplest stand
~10 kg, the umbilical cord ~12 kg and the services package ~90 kg.
The instrument may be used with either one or two position sensitive
proportional counters of 50 mm active length. A unique feature
(H) is the precisely controlled angular rotation of the X-ray tube about
the focal spot (a-rotation, Fig. 8(a)) combined with data manipulation
to allow accurate determination of the Bragg angles for specimens with
large grain size or pronounced gradients in crystallographic texture.
For single exposure measurements, only the a-rotation is used. With
a-rotation the diffraction peaks shift in the detectors, and hence the
a-rotation can be used to calibrate the position sensitivity of the
detectors.
For multiple exposure measurements, the X-ray tube and detector
(s) can be rotated simultaneously about the focal point (w-rotation,
Fig. 8(b)). The uniformity and concentricity of this rotation must be
precise, but a high degree of angular accuracy is not required. The a
and ai rotations are coplanar and the stress is determined in the direction
of the line of intersection between the plane of rotation and the
specimen surface.
Because the diffractometer is designed to measure stresses in
structures as well as small specimens, the design incorporates stages to
position the diffractometer relative to the specimen. The adjustment
along the direction of the specimen normal is most critical and is incorporated
into the diffractometer head (Fig. 7). A position sensor is
provided to sense the position of the diffractometer in this direction,
relative to the specimen surface, and allow accurate automatic positioning.
The diffractometer head also rotates about the specimen normal
(^-rotation) to allow stress measurement in any direction in the specimen
surface.
Translations in the plane of the specimen surface are provided
to allow one or two dimensional mapping of stress. The stages providing
these motions will be part of a laboratory stand.
Table 1 summarizes the important features of the CANMET portable
stress diffractometer.
PERFORMANCE OF THE CANMET DIFFRACTOMETER
To date, some aspects of the design have been evaluated with an
engineering version of the diffractometer.