Crack Growth
The subcritical nature of propagation may be attributed to the chemical energy released as the crack propagates. That is,
- elastic energy released + chemical energy = surface energy + deformation energy
The crack initiates at KIscc and thereafter propagates at a rate governed by the slowest process, which most of the time is the rate at which corrosive ions can diffuse to the crack tip. As the crack advances so K rises (because crack length appears in the calculation of stress intensity). Finally it reaches KIc, whereupon fast fracture ensues and the component fails. One of the practical difficulties with SCC is its unexpected nature. Stainless steels, for example, are employed because under most conditions they are "passive", i.e. effectively inert. Very often one finds a single crack has propagated while the rest of the metal surface stays apparently unaffected. The crack propagates perpendicular to the applied stress.
Read more about this topic: Stress Corrosion Cracking
Famous quotes containing the words crack and/or growth:
“You must be wise, in order to sniff out and weigh these mighty books, and swift in the hunt and brave in the battle; then, by careful reading and frequent reflection, crack open the bone and suck out the substantific marrow.”
—François Rabelais (1494–1553)
“When I have plucked the rose,
I cannot give it vital growth again,
It needs must wither. I’ll smell it on the tree.”
—William Shakespeare (1564–1616)