The diagram accompanying this problem (see Pg. 586 of the textbook), represents an exercise in orienting a crystal using the two surface method. It is an important procedure both for determining the orientation of a crystal, as well as for determining the indices of a twinning mode. The crystal is assumed to have a rectangular cross?section and to have twinned on three twinning planes. The resulting twin traces have been measured with respect to a vertical edge of the crystal which is parallel to the stress axis of the crystal.

Question

Then angles, thus obtained, are shown in the figure. Orient this crystal, by the two?surface technique, using the steps listed below.

(a) Lay out a stereographic projection on a sheet of tracing paper, with the front face of the crystal as the basic circle and the top of this circle the stress axis.

(b) Plot the twin traces orientations corresponding to the front face around the basic circle.

(c) Draw the great circle corresponding to the right side of the crystal and plot on this circle the corresponding twin trace orientations.

(d) Draw in the three great circles representing the twinning planes. Plot the poles of these three planes.

(e) Using the geometry of the fcc crystal structure, locate the position of a cube pole; that is {100}. Plot this on the figure.

(f) Now rotate the stereographic projection into a standard (100) projection, making sure that the stress axis is also rotated. In order to simplify the process, this last step should be performed on a second sheet of tracing paper.

(g) Draw the boundaries of the standard stereographic triangle that surround the stress axis, thus defining the stress axis orientation.

Answer 1