Page 149 - Microtectonics

138 5 · Shear Zones

Box 5.4 Continued
Fig. B.5.2. Rotational behaviour of ellipses with aspect ratio R =3
but different initial orientation in simple shear (grey curves) and
in general flow with W k = 0.89 (black curves). In simple shear,
the ellipses rotate permanently irrespective of their initial orien-
tation. At W k = 0.89 such ellipses reach a stable position. Some
ellipses can be seen to actually rotate backwards towards the
stable position. (Calculations by Sara Coelho)

Fig. B.5.3.
Groups of rigid elliptical ob-
jects with different orienta-
tion can reach a periodic
strong preferred orientation
in simple shear flow at cer-
tain finite strain values and
also rotate periodically to
their initial orientation with-
out preferred orientation.
a Behaviour of elliptical ob-
jects with an aspect ratio of
R =3. Inset shows the intial
orientation (position I) and a
strain value with strong pre-
ferred orientation (position II);
b behaviour of elliptical ob-
jects with an aspect ratio of
R = 10. Since these elongate
objects have a longer slow-
rotation period than those
with low aspect ratio, only
part of the rotation cycle is
shown at a similar scale as a;
the full pattern is shown in
the inset. (After Marques and
Coelho 2003)