Once a crack is initiated, tensile forces (stresses), which were contained prior to the event of cracking, are released. These released tensile forces (stresses) are captured by the material at the leading tips of the crack, thereby greatly increasing the intensity of the stress field and the likelihood of continued cracking at that point and all points forward. The terms stress riser and stress intensity factor are used to identify and quantify the increase in the stress field at the tips of a crack. If these regions contain and adequately respond to this increased burden, then the cracks will not propagate; if they do not, crack propagation will result. This characterizes the mechanism of slow crack growth. Stress risers are proportional to the measure of stress. Cracks will not propagate in a stress-free environment or where the level of stress at the tip of a crack is at a sufficiently low threshold. When the tip of a propagating crack leaves a crystal, it enters the disordered, non-layered, more loosely packed, tangled molecules of the amorphous region where the energy associated with
the stress field is partially dissipated as the tangled mass of molecules adjusts in time to the sustained forces.