It has been demonstrated by the authors [24] that by
attaching four electrodes at selected positions near the
tip of the pre-notch of the shear specimen, it is possible
to obtain electrical measurements which can be correlated
to the actual length of the propagating crack, provided that
the crack is straight and does not deviate from the transverse
axis of symmetry of the specimen. According to this
technique, the four electrodes A, L, R and B are welded at
intervals of 1.5 mm along a line starting at the tip of the
artificial pre-notch and running parallel to the long axis
of symmetry of the specimen (Fig. 5)