TABLE OF CONTENTS The conventional notation for the position of a point relative to the crack tip, and for the stresses at this point, is shown in Figure A.1. The point on the crack tip is the origin of the coordinate system and the z axis lies along the crack tip. Displacements of points within the cracked body when the body is loaded are u, v, w in the x, y, z directions. The terms crack tip and crack front are synonymous. Crack tip tends to be used for two dimensional situations and crack front in three dimensions.
A fundamental fracture mechanics concept is that of crack surface displacement. In fracture mechanics the interest is in what happens in the vicinity of the crack tip, so it is sometimes referred to as crack tip surface displacement. If a load is applied to a cracked body, then the crack surfaces move relative to each other. For points on opposing crack surfaces that were initially in contact there are three possible modes of crack surface displacement (Figure A.2); Mode I where opposing crack surfaces move directly apart in directions parallel to the y axis; Mode II where crack surfaces move over each along the x axis, that is, perpendicular to the crack tip; and Mode...
