Crack 4 : A stress-induced separation of the metal which, without any other influence, is insufficient in extent to cause complete rupture of the material. (Bul 5T1)
The Mudblogger (Oilfield, Energy and Related Photographs), Oil Field Glossary, TX, USA 2014. http://mudblogger.com/oilfield-glossary/, (Oil - Amer) {777}