FIFTH CANADIAN CONFERENCE ON NONDESTRUCTIVE ... - IAEA

- 374 -
define the axes u, v and w where w is the projection of m into the specimen
surface. The angles * and 0 define the orientation of m, u, v
relative to x, y and z.
The elastic strain along m is
d d-d d-d
n m _ in o „, m o
G s j_n
m d d d
o o
where: dm is the interplanar spacing along m,
d0 is the interplanar spacing with no stress and
the change from the exact value d0 to the approximate value
d, causes only a small error in era.
Then:
em = ew(cos 2 ip) YUW cosipsini|/
and, for material exhibiting isotroplc elasticity:
uw
uw
G
where: ew, eu, yuw are normal and shear strains in the u,
v, w coordinate system,
a u> a v> a w anc ' T uw are n 01 "" 13 ! an( l shear stresses
in the u, v, w coordinate system
E, v, G are Young's modulus, Poisson's ratio and the shear
modulus.
The X-rays normally sample only a thin surface layer in which
stress and structure gradients are small. With no surface tractions
= Tuw = 0
Eq.
Eq. 3
Eq. 3a
Eq. 3b
Eq. 3c